Open Access
How to translate text using browser tools
1 December 2001 Regulation of the Ion-Transporting Mitochondrion-Rich Cell during Adaptation of Teleost Fishes to Different Salinities
Tatsuya Sakamoto, Katsuhisa Uchida, Shigefumi Yokota
Author Affiliations +

The mitochondrion-rich cells (MRCs) in teleost gill and equivalent tissues are important osmo-regulatory sites in maintaining ionic balance. These cells express a variety of ion pumps, transporters, and channels, which play central roles in ionic regulation. Recently, two types of MRCs have been identified in euryhaline fishes: seawater (SW)-type MRCs extrude Na and Cl ions in SW conditions; freshwater (FW)-type MRCs take up at least Cl. Long-term development/differentiation of the two types of MRCs during adaptation to different salinities appears to be regulated mainly by endocrine factors. Osmolality, Ca2 , neurotransmitters, and fast-acting hormones rapidly regulate the SW MRCs. Recent information is assembled in this review and suggests the functional plasticity of highly specialized MRCs.


Mechanisms of teleost osmoregulation have been described in several reviews (e.g., Silva et al., 1977; Evans, 1979, 1993). Briefly, SW fishes lose water and gain ions through the body surface, mainly through the gills. In order to compensate for the osmotic loss of water, they drink the surrounding SW and absorb both ions and water from the intestine. Excess Na+ and Cl ions, which enter the body through the surface as well as via the intestine, are excreted by the gills. In contrast, FW fishes continuously need to dispose of water that enters through the body surface. The latter type of fish produces a large amount of hypotonic urine and they drink very little water. The passive loss of ions in the urine and across the body surface is compensated for by active ion uptake through the gills. Thus, the ionic exchange required for teleost osmoregulation is mainly located in the gill epithelium.

About 50 years ago, Keys and Willmer (1932) suggested that a certain type of gill epithelial cell might be responsible for Cl excretion in the SW-adapted eel. Later, Copeland (1948) described such cells, presumably for the first time, and referred to them as “chloride cells” in the killifish, Fundulus heteroclitus. These cells contain elaborate basolateral infoldings that produce an extensive intracellular tubular system associated with the ion-transporting enzyme Na+,K+ATPase (Karnaky et al., 1976) and numerous prominent mitochondria (e.g., Laurent, 1984). Therefore, these cells are also often referred to as “mitochondrion-rich cells (MRCs)”. Mature MRCs that come into contact with their external water via the apical membrane are involved in ion transport, though the tubular system is already developed in immature MRCs (Wendelaar Bonga and van der Meij, 1989; Goss et al., 1998). MRCs are interspersed among pavement cells which occupy more than 90% of the gill surface (Perry and Walsh, 1989). Tight junctions between MRCs and adjacent pavement cells are also considered to be “deep junctions” because of their multi-strand connections (Sardet et al., 1979; Sardet, 1980; Karnaky, 1992).

MRCs are found especially in the interlamellar epithelium and in the trailing edge of the filament epithelia of the gills. In some species, a considerable number of MRCs are observed in the gill lamellar epithelia (e.g., Laurent, 1984). MRCs are not necessarily confined to gill epithelia; they are also found in the inner surface of the operculum of the killifish Fundulus heteroclitus (e.g., Degnan et al., 1977), tilapia Oreochromis mossambicus (Foskett et al., 1981), and goldfish (Fujimoto, personal communication), and in the skin of gobies (Marshall and Nishioka, 1980; Yokota et al., 1997). In the embryos and larvae of several teleost species, MRCs have been detected in the epithelia covering the yolk and body surface (see Kaneko et al., 2002 for review). Most of these extrabranchial MRCs are found in the vascularized epithelia of the body surface; they may compensate for insufficient ion-transport in undeveloped or vestigial gills.

Regulation of MRCs is critical for euryhaline fish during movement between FW and SW. Reviews on this general topic have appeared previously (Foskett et al., 1983; McCormick, 1995; Marshall, 1995; Perry, 1997; Marshall and Bryson 1998; Evans et al., 1999). However, recent advances in molecular biology methods have allowed the determination of the function and regulation of MRCs. Such techniques involve the use of antibodies and molecular probes for ion-transporting proteins and hormonal factors. This review first considers current models of NaCl transport systems in MRCs in teleosts, especially those at the molecular and cellular levels, and then focuses primarily on recently obtained important evidence regarding the regulation of MRCs when teleost fish are exposed to different osmotic environments. Possible involvement of the gill MRCs in acid-base regulation, nitrogen excretion, and Ca2+ regulation will not be addressed here; these topics have been reviewed in detail elsewhere (Flik et al., 1995, 1996; Claiborne, 1998; Walsh, 1998; Evans et al., 1999).


In marine teleosts, and euryhaline species acclimated to SW, the mucosal surface of MRCs is usually invaginated below the pavement cells; this forms “apical crypts” between pavement cells. The MRCs usually display multicellular complexes and a well-developed intracellular tubular network (Hossler et al. 1979; Laurent 1984). Adjacent MRCs share an apical crypt and a single-stranded shallow junction. The same paracellular pathways are also observed between MRCs and accessory cells which is considered to be partially differentiated MRCs (e.g., Laurent, 1984). These “leaky” paracellular pathways are thought to be the morphological basis for the relatively high ionic permeability of gills in SW teleosts (e.g., Karnaky, 1992).

Inhibition of the efflux of Na+ and Cl by basolateral application of ouabain (an inhibitor of Na+,K+-ATPase) suggests that Na+,K+-ATPase generates an electrochemical gradient for Na+ from the plasma to the cytoplasm of the MRC to drive Na+ inward across the basolateral membrane (Silva et al.; 1977: Degnan et al.; 1977). Studies with the opercular membrane demonstrated that, under short-circuited conditions, the net Cl extrusion rate (serosa to mucosa) was equal to the short-circuit current, but there was no net extrusion of Na+. Basolateral application of furosemide (an inhibitor of the Na+-K+-2Cl cotransporter family) inhibited the net extrusion of Cl- (e.g., Degnan et al., 1977; Eriksson and Wistrand, 1986; Marshall, 1995; Payne and Forbush, 1995; Kaplan et al., 1996). Using the vibrating probe technique, Foskett and Scheffey (1982) demonstrated that the MRCs are the definite site of active Cl extrusion. An apical Cl channel seems to be a member of the cystic fibrosis transmembrane conductance regulator (CFTR) family because of its electrical characteristics and stimulation by cyclic AMP (Marshall et al., 1995). Ba2+ sensitivity of the serosal surface suggests the presence of a basolateral K+ channel (Degnan, 1985). Apical K+ secretion was also observed in short-circuited skin (Marshall and Bryson, 1998). The fine-tuned current model for NaCl extrusion by the teleost gill epithelium resulting from these studies is best described in detail in a review by Marshall (1995): The Na+ gradient, which is produced across the basolateral membrane by Na+,K+ATPase, drives the Na+-K+-2Cl cotransporter; K+ enters via the basolateral Na+,K+-ATPase and Na+-K+-2Cl cotransport, and the K+ is thought to be recycled from the cell via K+ channels; Cl exits the cell via an apical Cl channel and K+ via a basolateral K+ channel, resulting in a serosa-positive transepitherial potential that moves Na+ through the leaky para-cellular pathway between adjacent cells (see also Fig. 2, SW-type).

Recent reports have shown that Na+-K+-2Cl cotransporter immunoreactivity is localized on the basolateral membrane of the MRCs; such studies have also demonstrated the presence of a CFTR-like anion channel in the apical crypt (Singer et al., 1998; Wilson et al., 2000b). A cDNA for an inward rectifier K+ channel in the basolateral membrane has been identified in SW-adapted eels as an inducible mRNA (Suzuki et al., 1999). Miyazaki et al. (1999) have cloned two Cl channels (CLC-3 and 5) as intracellular Cl- channels from the tilapia gill.


In FW teleosts, MRCs in the gill filament epithelium are as abundant as in SW fish, but they may also appear on the lamellar epithelium in several species (e.g., Uchida et al., 1996; Perry, 1997; Hirai et al., 1999; Sasai et al., 1999). The MRCs observed in FW fish generally have apical microvilli, which presumably increase the mucosal surface area and extensive tight junctions between adjacent cells (Hwang, 1988; Perry et al., 1992; Marshall et al., 1997). In addition, MRCs in FW fish contain a moderately developed tubular system in the cytoplasm. Despite several exceptions, FW MRCs are often reported to be singular with their mucosal surface above the adjacent pavement cells (Hwang, 1988; Van Der Heijden et al., 1997; Marshall et al., 1997). Accessory cells are also found in several species in FW, although they are more typically found in SW fishes (Pisam et al., 1989; Cioni et al., 1991).

It is generally accepted that Cl uptake occurs via the MRCs because the morphological characteristics of the MRCs correlate well with Cl uptake rates (e.g., Perry and Laurent, 1989; Goss et al., 1994; Wood and Marshall, 1994; Marshall et al., 1997). Apical Cl/HCO3 exchange is assumed to mediate Cl uptake across the gill in FW conditions; inhibitors of the Cl/HCO3 exchanger reduce Cl uptake and produce a metabolic alkalosis in fish, as does the removal of external Cl (reviewed in Perry, 1997; Goss et al., 1998). Furthermore, the Cl/HCO3 exchanger was shown to be localized in MRCs using in situ hybridization and immunocytochemical staining (Sullivan et al., 1996; Wilson et al., 2000a). It remains unclear what drives this exchanger, since the Cl gradient between the cytoplasm and FW does not favor uptake of Cl ions from FW, and the true apical HCO3 gradient is unknown. Presumably, net Cl movement across the gill may be mediated via a basolateral Cl channel, driven by the inside-negative membrane potential for regular cells. The intracellular generation of H+ and HCO3 necessary for these apical extrusion mechanisms is probably derived from the hydration of CO2, since carbonic anhydrase has been localized in the opercular epithelium MRCs in the killifish (Lacy, 1983), and inhibition of carbonic anhydrase by acetazolamide reduced proton excretion (Lin and Randall, 1991).

Branchial uptake of Na+ is most probably via the apical Na+ channel, and down an electrochemical gradient generated by an apical vacuolar H+-ATPase, although the Na+/H+ exchange mechanism cannot be ignored (see Evans et al., 1999; Fenwick et al. 1999). There is some debate about the cellular localization of H+-ATPase and Na+ channels. With in situ hybridization and/or immunocytochemistry, the H+-ATPase has been reported to be localized in the pavement cells of the gill epithelium of rainbow trout (Sullivan et al., 1995, 1996) and of the yolk-sac membrane of the tilapia (Hiroi et al., 1998). Recently, immunoreaction for H+-ATPase and Na+ channel in both tilapia and rainbow trout were co-localized in the pavement cells (Wilson et al., 2000a), although apical labeling was also found in the MRCs of FW trout whose environmental pH and ionic strength are lower than those reported by Sullivan et al. (1995, 1996). The amiloride-sensitive Na+/H+ exchanger immunoreactivity is associated with the accessory cells and with a small population of pavement cells in tilapia (Wilson et al., 2000a) and with MRCs in Japanese dace (Kaneko, personal communication).

In order to determine the cellular site of Na+ uptake, and also to advance our understanding of MRC ion-transport, more species should be examined under a variety of physiological conditions using the antibodies and the molecular probes for ion-transporting proteins described above. Another powerful tool for the measurement of ion movement includes the use of ion-sensitive fluorescent dyes in combination with confocal laser scan microscopy (see Li et al., 1997).


When euryhaline teleosts adaptable to both FW and SW are transferred to different salinities, they show a sharp change in the rate of NaCl flux during the first hour of transition. The initial rapid change is followed by a more protracted change (hours - days) in the rate and direction of ion movement (e.g., Motais et al., 1966; Wood and Marshall, 1994). Therefore, the above-mentioned two functions of MRCs are likely to be skillfully regulated during adaptation to different salinities (see Table 1).

Table 1

Time course of adaptations to different salinities and regulations of mitochondrion-rich cells (MRCs)


Rapid Regulation (minutes to hours)

Euryhaline teleosts, especially intertidal species, need to regulate the rate of NaCl transport in the MRCs within several hours. River mouth intertidal habitats are subject to extreme tidal changes that result in rapid and frequent alternations in environmental salinity.

Marshall (1995) has reviewed the role of neurotransmitters and classical rapid-acting hormones on MRC function. Urotensins, eicosanoids, glucagon, and vasoactive intestinal polypeptides influence Cl secretion by MRCs, although it is not clear whether or not the MRCs are exposed to these hormones during adaptation to different salinities. Marshall et al. (1993, 1998) have shown that a portion of the stress-induced rapid reduction in Cl secretion may be mediated by the α2-adrenergic receptor activated by the sympathetic nervous system in killifish. This adrenergic receptor acts via phospholipase C, inositol triphosphate and intracellular Ca2+. Scheide and Zadunaisky (1988) showed that atrial natriuretic peptide (ANP), recognized as a SW-adapting hormone (Takei, 2000), directly increases Cl secretion. The role of other natriuretic peptides should be examined, since three types of natriuretic peptide receptors have been identified in the gills of eels (see Takei, 2000). Angiotensin II is also a SW-adapting hormone; it increases gill MRC Na+,K+-ATPase in the eel within 30 min. and receptors for angiotensin II are present in the MRCs (Marsigliante et al., 1997; Russel et al., 2001). There are also several instances where rapid activation of gill Na+,K+-ATPase has been reported after transfer of the killifish, mullet, or tilapia to conditions of higher salinity (Towle et al., 1977; Hossler, 1980; Hwang et al., 1989; Mancera and McCormick, 2000). The activation of the Na+,K+-ATPase in killifish is induced 3 hr. after SW transfer by hyperosmolality in vitro, and is dependent on transcriptional and translational processes (Mancera and McCormick, 2000). Cortisol, which increases rapidly following exposure to SW (see Shreck, 1981; Wendelaar Bonga, 1997), seems to directly activate gill MRC Na+,K+-ATPase in the eel within 2–6 hr. (Marsigliante et al., 2000). Borski et al. (2000) have suggested that cortisol may act on teleost target cells through membrane-associated effector systems, as well as more slowly via changes in gene expression. Cyclic AMP-mediated phosphorylation by the activity of protein kinases seems to play a role in the rapid modulation of Na+,K+ATPase (Tipsmark and Madsen, 2001)

Furthermore, both increases and decreases in the osmolality of the basolateral side of the opercular epithelia in vitro (simulating early events during adaptation) evoke immediate increases and decreases, respectively, in the rate of Cl secretion in killifish from SW (Zadunaisky et al. 1995; Marshall et al., 2000). This regulation seems to be mediated by tyrosine phosphorylation of the CFTR upon MRC shrinkage and swelling, accompanied by epithelial conductance changes (see also Daborn et al., 2001).

In this regard, we have shown that the MRC apical crypts of the estuarine mudskipper close 30 min. after transfer from SW to FW in order to shut down salt secretion and passive ion loss. Such responses are reversible when fish are returned to SW (Sakamoto et al., 2000c). This morphological oscillation seems to be triggered by differences in osmolality and Ca2+ concentration between FW and SW. Increases and decreases in osmolality of the basolateral side of killifish opercular epithelia in vitro also evoke similar morphological changes, and the actin cytoskeleton is required to maintain crypt opening (Daborn et al., 2001; Yasunaga et al., 2001). Via these morphological alterations, generally, MRCs seem to control the availability of ion channel/transporters at the apical membrane to the external water; hence, MRCs appear to affect the rate of ion transport (see Goss et al., 1998; Pisam et al., 1990).

The combination of these events, both the regulation of active ion transport and the modification of ion diffusion, could account for the full regulation of NaCl flux during rapid adaptation. It is of note that cross-talk between intracellular mechanisms of these regulations occurs. In addition to physiological approaches involving inhibitors of the signal transduction and the measurement of the secondary messenger levels, new approaches of molecular and cellular biological should be used to elucidate the candidate protein kinases and other related enzymes (e.g., Sakamoto et al., 2000b; Hashimoto et al., 1997, 1998, 2000). Surprisingly, phosphorlylation of these proteins has not been widely analyzed in MRCs. However, antibodies against phosphorylated amino acids and the mammalian enzymes are currently available. Breakthroughs may proceed from studies involving the rapid, simultaneous measurement of ion transport and morphological or biochemical changes in MRCs. Caged second messengers may also be useful in this regards.

Importantly, such rapid regulation suggests the functional plasticity of highly differentiated MRCs, not only at the molecular level but also at the morphological level. It should be noted that most of these rapid regulatory processes have been observed in intertidal species.

Long-term Regulation (days to weeks)

For most teleost species examined to date, Cl-secretory MRCs in hyperosmotic environments increase in number (e.g., Shirai and Utida, 1970; Foskett et al., 1983) and size (e.g., Shirai and Utida, 1970; Pisam, 1981; Pisam et al., 1988). The apical area of the MRC is enlarged, and accessory cells gradually intrude into the MRCs and form a multicellular complex (e.g., Shiraishi et al., 1997; Hiroi et al., 1999). These morphological changes are accompanied by increased expression and activity of Na+,K+-ATPase (Kirschner, 1980; McCormick, 1995; Seidelin et al., 2000; Cutler et al., 2000; Sakamoto et al., 2001), several days after transfer of the fish from FW to SW. The Na+,K+-ATPase α -subunit gene is considered to be AP-1 responsive (Shull et al., 1990). Moreover, Kültz (1996) has reported the modification of the AP-1 transcriptional factor c-Jun in the gills after transfer of a goby Gillichthys mirabilis to different salinities. Expression of the CFTR, Na+-K+-2Cl cotransporter and cytoskeletal elements (e.g., actin-binding protein and a member of the Rho family known to control actin) was also shown to be elevated and seems to be involved in MRC function in SW conditions (Singer et al., 1998; Suzuki et al., 1999; Pelis et al., 2001; Yasunaga et al., 2001). It has recently become clear that actin directly regulates Na+,K+ATPase, the Cl- channel, and the Na+-K+-2Cl cotransporter in various cells (Nelson and Hammerton, 1989; Suzuki et al., 1993; Mills et al., 1994; Shapiro et al. 1991; Matthews et al. 1992).

Pisam and coworkers (1987) have described two types of MRCs, α - and β, present in the gill filament of FW species (loach and gudgeon) and euryhaline species (salmonids, guppy, and tilapia) in FW. The α -type MRCs are activated in the filamental epithelium of euryhaline fishes acclimated to SW and are thought to be the homologue of the Cl-secretory SW MRCs (Pisam et al., 1987, 1995). On the other hand, the β -type MRCs are observed only in FW-adapted fish, and these cells disappeared during SW adaptation. Two different types of MRCs were also identified in the gill filament and lamellar epithelia of salmonids (Uchida et al., 1996, 1997; Seidelin et al., 2000), guppy (Shikano and Fujino, 1998), seabass (Hirai et al., 1999), and eel (Sasai et al., 1999), on the basis of their location and response to SW/FW transfer. Filament MRCs were activated after exposure to SW, and inactivated in FW conditions. The incorporation of 5-blomo-2′-deoxyuridine into filament MRCs increased after SW transfer, suggesting that filament MRCs play important roles in SW conditions (Uchida and Kaneko, 1996). In contrast, lamellar MRCs were mainly observed in FW conditions and practically disappeared by apoptosis during SW adaptation. Fish exposed to low ion concentrations in FW displayed extensive proliferation of the MRCs on the lamellar epithelium (e.g., Perry and Laurent, 1993; Perry, 1997). These results suggest that lamellar MRCs are the possible site of ion uptake in FW conditions. Although the relationship between the β -type MRCs in the filament and lamellar MRCs is unclear, Hirai et al. (1999) suggest that the latter originates from the filament and migrates to the lamellae during FW adaptation. Recently, Wong and Chan (1999) confirmed by flow cytometry the heterogeneity of MRCs and they hypothesized that stem cells, but not FW MRCs, differentiate into SW-type MRCs in the adult eel gill. On the other hand, Hiroi et al. (1999) observed in vivo sequential changes in the MRCs of the tilapia yolk-sac membrane, and indicated that FW-type MRCs are transformed into SW-type MRCs during SW adaptation, thus suggesting the plasticity of MRCs. Further research using these sequential observations may show the inverse transformation of SW-type cells into FW-type cells and should also address the functional plasticity of the MRCs using ion-sensitive dyes. However, the plasticity of MRCs may be a characteristic of those cells in the transient yolk sac during early development.

Although Shiraishi et al. (2001) have recently showed that the MRCs of this yolk-sac membrane can differentiate independently of endocrine factors, they have been believed to mediate most of the above-mentioned slow responses of MRCs to different salinities. Since McCormick (1995) provides an excellent review of the hormonal regulation of MRCs, only the more recent research will be considered here.

Prolactin (PRL)

Prolactin, a FW-adapting hormone in teleosts (see Hirano et al., 1986), inhibits the development Cl--secretory SW-type MRCs and promotes the development of FW-type MRCs. Foskett et al. (1982) have postulated that PRL reduced MRC numbers and active transport of ions in SW-adapted fish. PRL treatment of SW-adapted tilapia resulted in a reduction of MRC size (Herndon et al., 1991). Pisam et al. (1993) reported that PRL injection into SW-adapted tilapia resulted in the appearance of the putative FW-type β MRCs, whereas the SW-formα MRCs were reduced in size. Although mammalian PRL sometimes increased gill Na+,K+-ATPase activity possibly through growth hormone (GH) receptors, homologous PRLs decrease the activity of Na+,K+-ATPase in tilapia (Flik et al., 1994; Sakamoto et al., 1997). Prolactin receptors have been found in gill MRCs (Auperin et al., 1994; Weng et al., 1997; Sandra et al., 2000; Prunet et al., 2000; Santos et al., 2001), suggesting the direct action of PRL on MRCs.

Growth hormone/insulin-like growth factor (IGF) axis

Despite being structurally related to PRL, GH, one of the essential SW-adapting hormones in salmonids, activates gill Na+,K+-ATPase activity and SW MRCs (see Sakamoto et al., 1993; Prunet et al., 1994; Seidelin and Madsen, 1999). This GH role may be a common feature of euryhaline teleosts such as killifish, tilapia, striped bass, silver seabream and mudskipper (see Sakamoto et al., 1997, 2000a, 2002; Mancera and McCormick, 1998; Kelly et al., 1999).

One important pathway for the GH action is through its major influence on IGF-I secretion. IGF-I, especially plasma IGF-I from the liver, seems to be primarily induced by GH (see Moriyama et al., 2000). In the gill epithelium, IGF-I seems to be localized in the interlamellar epithelium (Fig. 1; Richardson et al., 1995), and it is also induced by GH after transfer of trout and tilapia to SW (Sakamoto and Hirano, 1993; Sakamoto et al., 1995). The GH receptor has been characterized in rainbow trout gills, although there is no evidence for a direct action of GH on gill MRCs (Sakamoto and Hirano, 1991). IGFI has been shown to increase Na+,K+-ATPase activity, SW MRCs, and/or salinity tolerance in salmonids and killifish (see Mancera and McCormick, 1998; Seidelin et al., 1999; Seidelin and Madsen, 1999). When coho salmon were pretreated with GH, IGF-I directly stimulated gill Na+,K+-ATPase activity (Madsen and Bern, 1993). Thus, at least among salmonids, GH may stimulate differentiation of MRCs via the local production of IGF-I, whereas systemic IGF-I may act on the differentiated cells. This hypothesis is similar to the dual effector model for the promotion of growth (Green et al., 1985; Gray and Kelley, 1991).

Fig. 1

Localization of IGF-I mRNA at interlamellar space of the gill filament of rainbow trout, presumably in some of the MRCs (arrows).


Although IGF-II is another member of the IGF family expressed in gills (Chan et al., 1994; Chen et al., 1994; Duguay et al., 1996), human IGF-II had no effect on killifish osmo-regulation (Mancera and McCormick, 1998). Additional experiments using homologous peptides may be necessary to demonstrate a possible action of IGF-II on gill MRC function. IGF-binding proteins play several biological roles along the GH/IGF axis; IGF-binding proteins have also been identified in teleosts (see Siharath and Bern, 1993). Although the growth-inhibiting role of IGF-binding protein 2 in zebrafish has been reported recently (Duan et al., 1999), there is no report about the possible functions of IGF-binding proteins in MRCs. The role of IGF-binding proteins during the adaptation of teleosts to different salinities should be examined using cDNA probes and proteins.


In teleosts, cortisol, the major corticosteroid secreted by interrenal glands, used to be understood as the central hormone for SW adaptation. Cortisol directly stimulates gill Na+, K+-ATPase activity and differentiation of MRCs (McCormick and Bern, 1989; McCormick, 1990; Ayson et al., 1995). A mineralocorticoid/glucocorticoid response element has been identified in the human Na+,K+-ATPase α gene (Kolla et al., 1999). Presence of the cortisol receptor has been demonstrated by steroid-binding assay in the gill cytosol and nucleus of several euryhaline species (e.g., Sandor et al., 1984; Chakraborti et al., 1987). Translocation of the cortisol receptor to the nucleus seemed to be rapidly stimulated by the plasma cortisol increase (Weisbart et al., 1987) and regulated by a heat shock protein (Hsp90) (Pan et al., 2000; Yasunaga et al., 2001). By means of in situ hybridization and immunocytochemical staining of chum salmon gills, Uchida et al. (1998) found that the cortisol receptor was expressed in the filament MRCs of the SW fish more than in the FW fish, suggesting the involvement of cortisol in the maintenance of their function in SW conditions.

There is a strong interaction between GH and cortisol in the regulation of SW MRCs. GH/IGF-I and cortisol act in synergy to increase Na+,K+-ATPase activity, MRC number, and/or salinity tolerance (see Mancera and McCormick, 1998). GH stimulated gill cortisol receptor, and directly increased the sensitivity of the interrenal tissue to adrenocorticotropin (ACTH) in coho salmon (Young, 1988; Shrimpton et al., 1995; Shrimpton and McCormick, 1998). On the other hand, cortisol stimulates GH release in tilapia (Nishioka et al., 1985).

Cortisol seems to be involved in ion uptake in FW fish as well. Cortisol treatment of FW fish stimulated the whole-body uptake of Na+ and Cl ions, possibly by increasing gill H+ATPase activity as well as cell number, apical surface areas, and/or Na+,K+-ATPase density in MRCs (Perry et al, 1992; Dang et al., 2000). Cortisol receptors were also localized in the MRCs in the gill lamellar epithelium of FW chum salmon, as well as in undifferentiated cells at the interlamellar regions near the central venous sinus (Uchida et al., 1998). Thus, cortisol seems to have a dual and fundamental role, acting not only on SW-type MRC but also on FW-type MRCs.

Other slow-acting hormones

Thyroid hormones have been hypothesized to play a role in many developmental processes including that of MRCs (see Hoar, 1988). However, the reported roles of these hormones on MRCs are equivocal. In salmonids, though still contradictory, thyroid hormones seem to stimulate the activity of gill Na+,K+-ATPase and MRCs, possibly through their interaction with the GH/IGF-I axis and cortisol (Miwa and Inui, 1985; Young and Lin, 1988; Moav and McKeown, 1992; Leloup and Lebel, 1993; Shrimpton and McCormick, 1998). These processes may be a part of the smoltification process, which may be essentially regulated by thyroid hormones. However, in tilapia and summer flounder, thyroid hormones enhance the Na+,K+-ATPase and MRCs in FW conditions, favoring hyperosmoregulatory capacity (Dange, 1986; Schreiber and Specker 2000; Subash Peter et al., 2000).

Sex steroids have been shown to have a negative effect on the activity of SW MRCs, Na+,K+-ATPase, and salinity tolerance of salmonids (see Madsen and Korsgaard, 1991). This response may be related to the FW migration of sexually mature salmonids. Although receptors for thyroid hormones and sex steroids have been found in the gills (Bres and Eales, 1988; Lebel and Leloup 1989; MacLatchy and Eales, 1992; Pinter and Thomas, 1995), the cellular localization and direct action of these hormones are currently unknown; further research similar to the case of cortisol is clearly warranted.


Any summary of MRC regulation in teleost fishes must confront the diverse habitat (FW, SW, estuarine) and life history (sedentary, anadromous, catadromous, diadromous) of this large group. Our literature search may have revealed contradictory results among the findings. Nevertheless, we present an integrated model of salinity regulation of MRCs, although the universality of the model remains uncertain (Fig. 2). MRCs possess a suite of transport proteins for salt excretion in SW conditions and Cl uptake in FW conditions. The cellular junctions and/or cytoskeletal components such as tight junctions and actin have been suggested to play a role in the ion transport. However, as there is currently little information on this topic, future investigations will hope fully shed more light on their involvement.

Fig. 2

Integrated model of regulation of MRCs during adaptation to different salinities. Arrows and letters in red denote the regulations during SW adaptation, and those in blue during FW adaptation; broken arrows denote possible pathways. There are reports on FW MRCs containing apical H+-ATPase and Na+ channels. Evidence to date indicates that rapid regulation by osmolality, neurotransmitters, fast-acting hormones, and Ca2+ occurs in SW MRCs. Long-term development/differentiation of MRCs from immature cells (resting or stem cells) is regulated by endocrine factors. Cortisol seems to play a basic role in activating both FW and SW-type MRCs. PRL inhibits SW MRCs and promotes FW-type MRCs, whereas GH/IGF-I stimulates SW MRCs. Receptors for cortisol, PRL, and angiotensin II (Ang II) are localized in MRCs, suggesting direct action. See text for details.


Evidence to date indicates that rapid regulations occur at least in Cl-secretory SW MRCs. Hyperosmolality, Ca2+, angiotensin II, ANP, and cortisol rapidly activate the SW MRCs, whereas sympathetic nerve and hypoosmolality inactivate the cells at rest. Important advances in this area may come from the rapid, simultaneous measurement of ion transport as well as of morphological and biochemical changes in MRCs. Ion-sensitive dyes and fluorescent probes may be particularly valuable in this regard.

Long-term development/differentiation of MRCs seems to be regulated mainly by endocrine factors. Cortisol seems to play a fundamental role in promoting the development of both FW and SW-type MRCs. PRL inhibits SW MRCs and activates FW-type MRCs, whereas GH/IGF-I stimulates SW MRCs. Receptors for cortisol, angiotensin II, and PRL are localized in MRCs. FW-type MRCs can be transformed into SW-type MRCs, suggesting the plasticity of MRCs. One question of particular interest for further study would be to determine the intracellular cues for the de novo development of FW and SW MRCs, or for the changeover from one cell type to another. Transcriptional regulations of ion-transport proteins should be examined in order to answer these questions. Recently-developed DNA arrays containing cDNAs of various transcriptional factors may prove useful for such studies. Translocation of transport proteins may also be possible (see Nielsen et al., 1993).

Continued development of preparations with MRCs (e.g., Fletcer et al., 2000; Shiraishi et al., 2001), as well as combinations of the various ideas and methods from molecular biology, histology, and physiology will be especially powerful approaches to advancing our understanding of MRC regulation.


We thank Prof. Masaaki Ando, Dr. Toyoji Kaneko, and Prof. Tetsuya Hirano for valuable discussions and guidance. We are sincerely grateful to Prof. Howard A. Bern for his encouragement and critical reading of the manuscript. Appreciation is expressed to Dr. Susumu Hyodo for his help with the in situ hybridization (Fig. 1). The original research by the authors has been supported in part by grants-in-aid for scientific research from the Society for the Promotion of Science, the Ministry of Education, and Fisheries Agency, Japan.



B. Auperin, F. Rentier-Delrue, J. A. Martial, and P. Prunet . 1994. Characterization of a single prolactin (PRL) receptor in tilapia (Oreochromis niloticus) which binds both PRLI and PRLII. J Mol Endocrinol 13:241–251. Google Scholar


F. G. Ayson, T. Kaneko, S. Hasegawa, and T. Hirano . 1995. Cortisol stimulates the size and number of mitochondrion-rich cells in the yolksac membrane of embryos and larvae of tilapia (Oreochromis mossambicus) in vitro and in vivo. J Exp Zool 272:419–425. Google Scholar


R. J. Borski 2000. Nongenomic membrane actions of glucocorticoids in vertebrates. Trends Endocrinol Metab 11:427–436. Google Scholar


O. Bres and J. G. Eales . 1988. High-affinity, limited-capacity triiodothyro-nine-binding sites in nuclei from various tissues of the rainbow trout (Salmo gairdneri). Gen Comp Endocrinol 69:71–79. Google Scholar


P. K. Chakraborti, M. Weisbart, and A. Chakraborti . 1987. The presence of corticosteroid receptor activity in the gills of the brook trout, Salvelinus fontinalis. Gen Comp Endocrinol 66:323–332. Google Scholar


S. J. Chan and D. F. Steiner . 1994. Structure and expression of insulin-like growth factor genes in fish. In “Fish Physiology, vol XIII”. Ed by W. S. Hoar and D. Randall . Academic Press. New York. pp. 213–224. Google Scholar


T. T. Chen, A. Marsh, M. Shamblott, K-M. Chan, Y-L. Tang, C. M. Cheng, and B-Y. Yang . 1994. Structure and evolution of fish growth hormone and insulin-like growth factor genes. In “Fish Physiology, vol XIII”. Ed by W. S. Hoar and D. Randall . Academic Press. New York. pp. 179–209. Google Scholar


C. Cioni, D. De Merich, E. Cataldi, and S. Sataudella . 1991. Fine structure of chloride cells in freshwater-and seawater-adapted Oreochromis niloticus (Linnaeus) and Oreochromis mossambicus (Peters). J Fish Biol 39:197–209. Google Scholar


J. B. Claiborne 1998. Acid-base regulation. In “The Physiology of Fishes”. Ed by D. H. Evans CRC Press. Boca Raton. pp. 177–198. Google Scholar


D. E. Copeland 1948. The cytological basis of chloride transfer in the gills of Fundulus heteroclitus. J Morphol 82:201–227. Google Scholar


C. P. Cutler, S. Brezillon, S. Bekir, I. L. Sanders, N. Hazon, and G. Cramb . 2000. Expression of a duplicate Na,K-ATPase beta(1)-isoform in the European eel (Anguilla anguilla). Am J Physiol Regul Integr Comp Physiol 279:R222–R229. Google Scholar


K. Daborn, R. R. F. Cozzi, and W. S. Marshall . 2001. Dynamics of pavement cell? Chloride cell interactions during abrupt salinity change in Fundulus heteroclitus. J Exp Biol 204:1889–1899. Google Scholar


Z. Dang, P. H. Balm, G. Flik, S. E. Wendelaar Bonga, and R. A. Lock . 2000. Cortisol increases Na(+)/K(+)-ATPase density in plasma membranes of gill chloride cells in the freshwater tilapia Oreochromis mossambicus. J Exp Biol 203:2349–2355. Google Scholar


A. D. Dange 1986. Branchial Na+-K+-ATPase activity in freshwater or saltwater acclimated tilapia, Oreochromis (Sarotherodon) mossambicus: effects of cortisol and thyroxin. Gen Comp Endocrinol 62:341–343. Google Scholar


K. J. Degnan 1985. The role of K+ and Cl conductances in chloride secretion by the opercular membrane. J Exp Zool 231:11–17. Google Scholar


K. J. Degnan, K. J. Karnaky Jr, and J. Zadunaisky . 1977. Active chloride transport in the in vitro opercular skin of a teleost (Fundulus heteroclitus), a gill-like epithelium rich in chloride cells. J Physiol 271:155–191. Google Scholar


C. Duan, J. Ding, Q. Li, W. Tsai, and K. Pozios . 1999. Insulin-like growth factor binding protein 2 is a growth inhibitory protein conserved in zebrafish. Proc Natl Acad Sci U S A 96:15274–15279. Google Scholar


S. J. Duguay, J. Lai-Zhang, D. F. Steiner, B. Funkenstein, and S. J. Chan . 1996. Developmental and tissue-regulated expression of IGF-I and IGFII mRNAs in Sparus aurata. J Mol Endocrinol 16:123–132. Google Scholar


O. Eriksson and P. J. Wistrand . 1986. Chloride transport inhibition by various types of ‘loop’ diuretics in fish opercular epithelium. Acta Physiol Scand 126:93–101. Google Scholar


D. H. Evans 1979. Fish. In “Comparative Physiology of Osmoregulation in Animals Vol 1”. Ed by G. M. O. Maloiy Academic Press. Orlando. pp. 305–390. Google Scholar


D. H. Evans 1993. Osmotic and ionic regulation. In “The Physiology of Fishes”. Ed by D. H. Evans CRC Press. Boca Raton. pp. 315–341. Google Scholar


D. H. Evans, P. M. Piermarini, and W. T. W. Potts . 1999. Ionic transport in fish gill epithelium. J Exp Zool 283:641–652. Google Scholar


J. C. Fenwick, S. E. Wendelaar Bonga, and G. Flik . 1999. in vivo bafilomycin-sensitive Na(+) uptake in young freshwater fish. J Exp Biol 202:3659–3666. Google Scholar


M. Fletcher, S. P. Kelly, P. Part, M. J. O'Donnell, and C. M. Wood . 2000. Transport properties of cultured branchial epithelia from freshwater rainbow trout: a novel preparation with mitochondria-rich cells. J Exp Biol 203:1523–1537. Google Scholar


G. Flik, P. H. M. Klaren, T. J. M. Schoenmakers, M. J. C. Bijvelds, P. M. Verbost, and S. E. Wendelaar Bonga . 1996. Cellular calcium transport in fish: unique and universal mechanisms. Physiol Zool 69:403–417. Google Scholar


G. Flik, F. Rentier-Delrue, and S. E. Wendelaar Bonga . 1994. Calcitropic effects of recombinant prolactins in Oreochromis mossambicus. Am J Physiol 266:R1302–1308. Google Scholar


G. Flik, P. M. Verbost, and S. E. Wendelaar Bonga . 1995. Calcium transport processes in fishes. In “Cellular and Molecular Approaches to Fish Ionic Regulation”. Ed by C. M. Wood and T. J. Shuttleworth . Academic Press. San Diego. pp. 317–342. Google Scholar


J. K. Foskett, H. A. Bern, T. E. Machen, and M. Conner . 1983. Chloride cells and hormonal control of teleost fish osmoregulation. J Exp Biol 100:255–281. Google Scholar


J. K. Foskett, C. D. Logsdon, T. Turner, T. E. Machen, and H. A. Bern . 1981. Differentiation of the chloride extrusion mechanisms during seawater adaptation of a teleost fish, the cichlid Sarotherodon mossambicus. J Exp Biol 93:209–224. Google Scholar


J. K. Foskett, T. E. Machen, and H. A. Bern . 1982. Chloride secretion and conductance of teleost opercular membrane: effects of prolactin. Am J Physiol 242:R380–389. Google Scholar


J. K. Foskett and C. Scheffey . 1982. The chloride cell: definitive identification as the salt-secretory cell in teleosts. Science 215:164–166. Google Scholar


G. Goss, S. Perry, J. Fryer, and P. Laurent . 1998. Gill morphology and acid-base regulation in freshwater fishes. Comp Biochem Physiol 119A:107–115. Google Scholar


G. G. Goss, P. Laurent, and S. F. Perry . 1994. Gill morphology during hyper-capnia in brown bullhead (I. nebulosus): role of chloride cells and pavement cells in acid-base regulation. J Fish Biol 45:705–718. Google Scholar


E. S. Gray and K. M. Kelley . 1991. Growth regulation in the gobiid teleost, Gillichthys mirabilis: roles of growth hormone, hepatic growth hormone receptors and insulin-like growth factor-I. J Endocrinol 131:57–66. Google Scholar


H. Green, M. Morikawa, and T. Nixon . 1985. A dual effector theory of growth-hormone action. Differentiation 29:195–198. Google Scholar


H. Hashimoto, M. Fukuda, Y. Matsuo, Y. Yokoyama, E. Nishida, H. Toyohara, and M. Sakaguchi . 2000. Identification of a nuclear export signal in MKK6, an activator of the carp p38 mitogen-activated protein kinases. Eur J Biochem 267:4362–4371. Google Scholar


H. Hashimoto, Y. Matsuo, Y. Yokoyama, H. Toyohara, and M. Sakaguchi . 1997. Structure and expression of carp mitogen-activated protein kinases homologous to mammalian JNK/SAPK. J Biochem (Tokyo) 122:381–386. Google Scholar


H. Hashimoto, Y. Yokoyama, Y. Matsuo, H. Toyohara, M. Kohno, and M. Sakaguchi . 1998. Existence of two isoforms of extracellular signal-regulated kinase in fish. J Biochem (Tokyo) 123:1031–1035. Google Scholar


T. M. Herndon, S. D. McCormick, and H. A. Bern . 1991. Effects of prolactin on chloride cells in opercular membrane of seawater-adapted tilapia. Gen Comp Endocrinol 83:283–289. Google Scholar


N. Hirai, M. Tagawa, T. Kaneko, T. Seikai, and M. Tanaka . 1999. Distributional changes in branchial chloride cells during freshwater adaptation in Japanese sea bass Lateolabrax japonics. Zool Sci 16:43–49. Google Scholar


T. Hirano 1986. The spectrum of prolactin action in teleosts. Prog Clin Biol Res 205:53–74. Google Scholar


J. Hiroi, T. Kaneko, K. Uchida, S. Hasegawa, and M. Tanaka . 1998. Immunolocalization of vacuolar-type H+-ATPase in the yolk-sac membrane of tilapia (Oreochromis mossambicus) larvae. Zool Sci 15:447–453. Google Scholar


J. Hiroi, T. Kaneko, and M. Tanaka . 1999. in vivo sequential changes in chloride cell morphology in the yolk-sac membrane of Mozambique tilapia (Oreochromis mossambicus) embryos and larvae during seawater adaptation. J Exp Biol 24:3485–3495. Google Scholar


W. S. Hoar 1988. The physiology of smolting salmonids. In “Fish Physiology Vol XIB”. Ed by W. S. Hoar and D. J. Randall . Academic Press. Orlando. pp. 275–343. Google Scholar


F. E. Hossler 1980. Gill arch of the mullet, Mugil cephalus, III: rate of response to salinity change. Am J Physiol 238:R160–R164. Google Scholar


F. E. Hossler, J. R. Ruby, and T. D. McIlwain . 1979. The gills arch of the mullet, Mugil cephalus: II. Modification in surface ultrastructure and Na/ K-ATPase content during adaptation to various salinities. J Exp Zool 208:399–405. Google Scholar


P. P. Hwang 1988. Multicellular complex of chloride cells in the gills of freshwater teleosts. J Morphol 196:15–22. Google Scholar


P. P. Hwang, C. M. Sun, and S. M. Wu . 1989. Changes of plasma osmolality, chloride concentration and gill Na-K-ATPases activity in tilapia Oreochromis mossambicus during seawater acclimation. Mar Biol 100:295–299. Google Scholar


T. Kaneko, K. Shiraishi, F. Katoh, S. Hasegawa, and J. Hiroi . 2002. Chloride cells in early life stages of fish and their functional differentiation. Fish Sci press. Google Scholar


M. R. Kaplan, D. B. Mount, E. Delpire, G. Gamba, and S. C. Hebert . 1996. Molecular mechanisms of NaCl cotransport. Ann Rev Physiol 58:649–668. Google Scholar


K. J. Karnaky Jr 1992. Teleost osmoregulation: changes in the tight junction in response to the salinity of the environment. In “Tight junctions”. Ed by M. Cereijido CRC Press. Boca Raton. pp. 175–185. Google Scholar


K. J. Karnaky Jr, L. B. Kinter, W. B. Kinter, and C. E. Stirling . 1976. Teleost chlo-ride cell. II. Autoradiographic localization of gill Na,K- ATPase in killifish Fundulus heteroclitus adapted to low and high salinity environments. J Cell Biol 70:157–177. Google Scholar


A. B. Keys and E. N. Willmer . 1932. “Chloride-secreting cells” in the gill of fishes with special reference to the common eel. J Physiol 76:368–378. Google Scholar


S. P. Kelly, I. N. Chow, and N. Y. Woo . 1999. Effects of prolactin and growth hormone on strategies of hypoosmotic adaptation in a marine teleost, Sparus sarba. Gen Comp Endocrinol 113:9–22. Google Scholar


L. B. Kirschner 1980. Comparison of vertebrate salt-excreting organs. Am J Physiol 238:R219–R223. Google Scholar


V. Kolla, N. M. Robertson, and G. Litwack . 1999. Identification of a mineralocorticoid/glucocorticoid response element in the human Na/K ATPase alpha1 gene promoter. Biochem Biophys Res Commun 266:5–14. Google Scholar


D. Kültz 1996. Plasticity and stressor specificity of osmotic and heat shock responses of Gillichthys mirabilis gill cells. Am J Physiol 271:C1181–C1193. Google Scholar


E. R. Lacy 1983. Histochemical and biochemical studies of carbonic anhydrase activity in the opercular epithelium of the euryhaline teleost, Fundulus heteroclitus. Am J Anat 166:19–39. Google Scholar


P. Laurent 1984. Gill internal morphology. In “Fish physiology vol XA”. Ed by W. S. Hoar and D. J. Randall . Academic Press. Orlando. pp. 73–183. Google Scholar


J. M. Lebel and J. Leloup . 1989. Triiodothyronine binding to putative solubilized nuclear thyroid hormone receptor in liver and gill of the brown trout (Salmo trutta) and the European eel (Anguilla anguilla). Gen Comp Endocrinol 75:301–309. Google Scholar


J. Leloup and J. M. Lebel . 1993. Triiodothyronine is necessary for the action of growth hormone in acclimation to seawater of brown trout (Salmo trutta) and rainbow trout (Onchoryhnchus mykiss). Fish Physiol Biochem 11:165–173. Google Scholar


J. Li, J. Eygensteyn, R. Lock, S. Bonga, and G. Flik . 1997. Na+ and Ca2+ homeostatic mechanisms in isolated chloride cells of the teleost Oreochromis mossambicus analyzed by confocal laser scanning microscopy. J Exp Biol 200:1499–1508. Google Scholar


H. Lin and D. Randall . 1991. Evidence for the presence of an electrogenic proton pump on the trout gill epithelium. J Exp Biol 161:119–134. Google Scholar


D. L. MacLatchy and J. G. Eales . 1992. Intra- and extra-cellular sources of T3 binding to putative thyroid hormone receptors in liver, kidney, and gill nuclei of immature rainbow trout, Oncorhynchus mykiss. J Exp Zool 262:22–29. Google Scholar


S. S. Madsen and H. A. Bern . 1993. In-vitro effects of insulin-like growth factor-I on gill Na+,K+-ATPase in coho salmon, Oncorhynchus kisutch. J Endocrinol 138:23–30. Google Scholar


S. S. Madsen and B. Korsgaard . 1991. Opposite effects of 17 beta-estradiol and combined growth hormone-cortisol treatment on hypoosmoregulatory performance in sea trout presmolts, Salmo trutta. Gen Comp Endocrinol 83:276–282. Google Scholar


J. M. Mancera and S. D. McCormick . 1998. Osmoregulatory actions of the GH/IGF axis in non-salmonid teleosts. Comp Biochem Physiol B 121:43–48. Google Scholar


J. M. Mancera and S. D. McCormick . 2000. Rapid activation of gill Na(+),K(+)-ATPase in the euryhaline teleost Fundulus heteroclitus. J Exp Zool 287:263–274. Google Scholar


W. S. Marshall 1995. Transport processes in isolated teleost epithelia: opercular epithelium and urinary bladder. In “Cellular and Molecular Approaches to Fish Ionic Regulation”. Ed by C. M. Wood and T. J. Shuttleworth . Academic Press. San Diego. pp. 1–23. Google Scholar


W. S. Marshall and R. S. Nishioka . 1980. Relation of mitochondria-rich chlo-ride cells to active chloride transport in the skin of a marine teleost. J Exp Zool 214:147–156. Google Scholar


W. S. Marshall and S. E. Bryson . 1998. Transport mechanisms of seawater teleost chloride cells: an inclusive model of a multi-functional cell. Comp Biochem Physiol 119A:97–106. Google Scholar


W. S. Marshall, S. E. Bryson, P. Darling, C. Whitten, M. Patrick, M. Wilkie, C. M. Wood, and J. Buckland-Nicks . 1997. NaCl transport and ultra-structure of opercular epithelium from a freshwater-adapted euryhaline teleost, Fundulus heteroclitus. J Exp Zool 277:23–37. Google Scholar


W. S. Marshall, S. E. Bryson, and D. Garg . 1993. Alpha 2-adrenergic inhibition of Cl- transport by opercular epithelium is mediated by intracellular Ca2+. Proc Natl Acad Sci U S A 90:5504–5508. Google Scholar


W. S. Marshall, S. E. Bryson, A. Midelfart, and W. F. Hamilton . 1995. Low-conductance anion channel activated by cAMP in teleost Cl-secreting cells. Am J Physiol 268:R963–969. Google Scholar


W. S. Marshall, S. E. Bryson, and T. Luby . 2000. Control of epithelial Cl(–) secretion by basolateral osmolality in the euryhaline teleost Fundulus heteroclitus. J Exp Biol 203:1897–1905. Google Scholar


W. S. Marshall, R. M. Duquesnay, J. M. Gillis, S. E. Bryson, and C. M. Liedtke . 1998. Neural modulation of salt secretion in teleost opercular epithelium by 2-adrenergic receptors and inositol 1,4,5-trisphosphate. J Exp Biol 201:1959–1965. Google Scholar


S. Marsigliante, A. Muscella, S. Vilella, and C. Storelli . 2000. Dexamethasone modulates the activity of the eel branchial Na+/K+ATPase in both chloride and pavement cells. Life Sci 66:1663–1673. Google Scholar


S. Marsigliante, A. Muscella, G. P. Vinson, and C. Storelli . 1997. Angiotensin II receptors in the gill of sea water- and freshwater-adapted eel. J Mol Endocrinol 18:67–76. Google Scholar


J. B. Matthews, C. S. Awtrey, and J. L. Madara . 1992. Microfilament-dependent activation of Na+/K+/2Cl cotransport by cAMP in intestinal epithelial monolayers. J Clin Invest 90:1608–1613. Google Scholar


S. D. McCormick 1990. Cortisol directly stimulates differentiation of chloride cells in tilapia opercular membrane. Am J Physiol 259:R857–R863. Google Scholar


S. D. McCormick 1995. Hormonal control of gill Na+,K+-ATPase and chloride cell function. In “Cellular and Molecular Approaches to Fish Ionic Regulation”. Ed by C. M. Wood and T. J. Shuttleworth . Academic Press. San Diego. pp. 285–315. Google Scholar


S. D. McCormick and H. A. Bern . 1989. in vitro stimulation of Na+-K+ATPase activity and ouabain binding by cortisol in coho salmon gill. Am J Physiol 256:R707–R715. Google Scholar


J. W. Mills, E. M. Scwiebert, and B. A. Stanton . 1994. Evidence for the role of actin filaments in regulating cell swelling. J Exp Zool 268:111–120. Google Scholar


H. Miyazaki, S. Uchida, Y. Takei, T. Hirano, F. Marumo, and S. Sasaki . 1999. Molecular cloning of CLC chloride channels in Oreochromis mossambicus and their functional complementation of yeast CLC gene mutant. Biochem Biophys Res Commun 255:175–181. Google Scholar


S. Miwa and Y. Inui . 1985. Effects of L-thyroxin and ovine growth hormone on smoltification of amago salmon (Oncorhynchus rhodurus). Gen Comp Endocrinol 58:436–42. Google Scholar


B. Moav and B. A. McKeown . 1992. Thyroid hormone increases transcription of growth hormone mRNA in rainbow trout pituitary. Horm Metab Res 24:10–14. Google Scholar


S. Moriyama, F. G. Ayson, and H. Kawauchi . 2000. Growth regulation by insulin-like growth factor-I in fish. Biosci Biotechnol Biochem 64:1553–1562. Google Scholar


R. Motais, F. Garcia-Romeu, and J. Maetz . 1966. Exchange diffusion effect and euryhalinity in teleosts. J Gen Physiol 50:391–422. Google Scholar


W. J. Nelson and R. W. Hammerton . 1989. A membrane-cytoskeleton complex containing Na+,K+-ATPase, ankryin, and fodrin in MadinDarby canine kidney (MDCK) cells: Implications for the biogenesis of epithelial cell polarity. J Cell Biol 108:893–902. Google Scholar


S. Nielsen, S. R. DiGiovanni, E. I. Christensen, M. A. Knepper, and H. W. Harris . 1993. Cellular and subcellular immunolocalization of vasopressin-regulated water channel in rat kidney. Proc Natl Acad Sci U S A 90:11663–11667. Google Scholar


R. S. Nishioka, E. G. Grau, and H. A. Bern . 1985. in vitro release of growth hormone from the pituitary gland of tilapia, Oreochromis mossambicus. Gen Comp Endocrinol 60:90–94. Google Scholar


F. Pan, J. M. Zarate, G. C. Tremblay, and T. M. Bradley . 2000. Cloning and characterization of salmon hsp90 cDNA: upregulation by thermal and hyperosmotic stress. J Exp Zool 287:199–212. Google Scholar


J. A. Payne and B. Forbush III . 1995. Molecular characterization of the epithelial Na-K-Cl cotransporter isoforms. Curr Opin Cell Biol 7:493–503. Google Scholar


R. M. Pelis, J. Zydlewski, and S. D. McCormick . 2001. Gill Na(+)-K(+)-2Cl(–) cotransporter abundance and location in Atlantic salmon: effects of seawater and smolting. Am J Physiol 280:R1844–1852. Google Scholar


S. F. Perry 1997. The chloride cell: structure and function in the gills of freshwater fishes. Annu Rev Physiol 59:325–347. Google Scholar


S. F. Perry, G. G. Goss, and P. Laurent . 1992. The interrelationships between gill chloride cell morphology and ionic uptake in four freshwater teleosts. Can J Zool 70:1775–1786. Google Scholar


S. F. Perry and P. Laurent . 1989. Adaptational responses of rainbow trout to lowered external NaCl concentration: Contribution of the bran-chial chloride cell. J Exp Biol 147:147–168. Google Scholar


S. F. Perry and P. Laurent . 1993. Environmental effects on fish gill structure and function. In “Fish ecophysiology”. Ed by J. C. Rankin and J. B. Jensen . Chapman & Hall. London. pp. 231–264. Google Scholar


S. F. Perry and P. J. Walsh . 1989. Metabolism of isolated fish gill cells: contribution of epithelial chloride cells. J Exp Biol 144:507–520. Google Scholar


J. Pinter and P. Thomas . 1995. Characterization of a progestogen receptor in the ovary of the spotted seatrout, Cynoscion nebulosus. Biol Reprod 52:667–675. Google Scholar


M. Pisam 1981. Membranous systems in the “chloride cell” of teleostean fish gill; their modifications in response to the salinity of the environment. Anat Rec 200:401–414. Google Scholar


M. Pisam, B. Auperin, P. Prunet, F. Rentier-Delrue, J. Martial, and A. Rambourg . 1993. Effects of prolactin on alpha and beta chloride cells in the gill epithelium of the saltwater adapted tilapia “Oreochromis niloticus”. Anat Rec 235:275–284. Google Scholar


M. Pisam, G. Boeuf, P. Prunet, and A. Rambourg . 1990. Ultrastructural features of mitochondria-rich cells in stenohaline freshwater and seawater fishes. Am J Anat 187:21–31. Google Scholar


M. Pisam, A. Caroff, and A. Rambourg . 1987. Two types of chloride cells in the gill epithelium of a freshwater-adapted euryhaline fish: Lebistes reticulatus; their modifications during adaptation to salt-water. Am J Anat 179:40–50. Google Scholar


M. Pisam, C. Le Moal, B. Auperin, P. Prunet, and A. Rambourg . 1995. Apical structures of “mitochondria-rich” alpha and beta cells in euryha-line fish gill: their behaviour in various living conditions. Anat Rec 241:13–24. Google Scholar


M. Pisam, P. Prunet, G. Boeuf, and A. Rambourg . 1988. Ultrastructural features of chloride cells in the gill epithelium of the Atlantic salmon, Salmo salar, and their modifications during smoltification. Am J Anat 183:235–44. Google Scholar


M. Pisam, P. Prunet, and A. Rambourg . 1989. Accessory cells in the gill epithelium of the freshwater rainbow trout Salmo gairdneri. Am J Anat 184:311–320. Google Scholar


P. Prunet, M. Pisam, J. P. Claireaux, G. Boeuf, and A. Rambourg . 1994. Effects of growth hormone on gill chloride cells in juvenile Atlantic salmon (Salmo salar). Am J Physiol 266:R850–R857. Google Scholar


P. Prunet, O. Sandra, P. Le Rouzic, O. Marchand, and V. Laudet . 2000. Molecular characterization of the prolactin receptor in two fish species, tilapia Oreochromis niloticus and rainbow trout, Oncorhynchus mykiss: a comparative approach. Can J Physiol Pharmacol 78:1086–1096. Google Scholar


N. A. Richardson, A. J. Anderson, M. A. Rimmer, and V. R. Sara . 1995. Localization of insulin-like growth factor-I immunoreactivity in larval and juvenile barramundi (Lates calcarifer). Gen Comp Endocrinol 100:282–292. Google Scholar


M. J. Russell, A. M. Klemmer, and K. R. Olson . 2001. Angiotensin signaling and receptor types in teleost fish. Comp Biochem Physiol A Mol Integr Physiol 128:41–51. Google Scholar


T. Sakamoto, T. Agustsson, B. Th Björnsson, and M. Ando . 2000a. Roles of growth hormone and prolactin during adaptation of the gobies to various environments. In “Growth and Growth Regulation in Fish”. Ed by Th Bjornsson and D. MacKinlay . American Fisheries Society. Vancouver. pp. 29–32. Google Scholar


T. Sakamoto and T. Hirano . 1991. Growth hormone receptors in the liver and osmoregulatory organs of rainbow trout: characterization and dynamics during seawater adaptation. J Endocrinol 130:425–433. Google Scholar


T. Sakamoto and T. Hirano . 1993. Expression of insulin-like growth factor I gene in osmoregulatory organs during seawater adaptation of the salmonid fish: Possible mode of osmoregulatory action of growth hormone. Proc Natl Acad Sci USA 90:1912–1916. Google Scholar


T. Sakamoto, K. Iwata, and M. Ando . 2002. Growth hormone and prolactin expression during environmental adaptation of gobies. Fish Sci in press. Google Scholar


T. Sakamoto, T. Kozaka, A. Takahashi, H. Kawauchi, and M. Ando . 2001. Medaka, Oryzias latipes, as a model for hypoosmoregulation of euryhaline fishes. Aquaculture 193:347–654. Google Scholar


T. Sakamoto, S. D. McCormick, and T. Hirano . 1993. Osmoregulatory actions of growth hormone and its mode of action in salmonids: A review. Fish Physiol Biochem 11:155–164. Google Scholar


T. Sakamoto, N. Ojima, and M. Yamashita . 2000b. Induction of mRNAs in response to acclimation of trout cells to different osmolalities. Fish Physiol Biochem 22:255–262. Google Scholar


T. Sakamoto, B. S. Shepherd, R. S. Nishioka, S. S. Madsen, K. Siharath, H. A. Bern, and E. G. Grau . 1995. Osmoregulatory actions of growth hormone in an advanced teleost. Am. Zool 34:43A. Google Scholar


T. Sakamoto, B. S. Shepherd, R. S. Nishioka, S. S. Madsen, K. Siharath, N. H. Richman III, H. A. Bern, and E. G. Grau . 1997. Osmoregulatory actions of growth hormone and prolactin in an advanced teleost. Gen Comp Endocrinol 106:95–101. Google Scholar


T. Sakamoto, S. Yokota, and M. Ando . 2000c. Rapid morphological oscillation of mitochondrion-rich cell in estuarine mudskipper following salinity changes. J Exp Zool 286:666–669. Google Scholar


T. Sandor, J. A. DiBattista, and A. Z. Mehdi . 1984. Glucocorticoid receptors in the gill tissue of fish. Gen Comp Endocrinol 53:353–64. Google Scholar


O. Sandra, P. Le Rouzic, C. Cauty, M. Edery, and P. Prunet . 2000. Expression of the prolactin receptor (tiPRL-R) gene in tilapia Oreochromis niloticus: tissue distribution and cellular localization in osmoregulatory organs. J Mol Endocrinol 24:215–224. Google Scholar


C. R. Santos, P. M. Ingleton, J. E. Cavaco, P. A. Kelly, M. Edery, and D. M. Power . 2001. Cloning, Characterization, and Tissue Distribution of Prolactin Receptor in the Sea Bream (Sparus aurata). Gen Comp Endocrinol 121:32–47. Google Scholar


C. Sardet 1980. Freeze fracture of the gill epithelium of euryhaline teleost fish. Am J Physiol 238:R207–212. Google Scholar


C. Sardet, M. Pisam, and J. Maetz . 1979. The surface epithelium of teleostean fish gills: cellular and junctional adaptations of the chloride cell in relation to salt adaptation. J Cell Biol 80:96–117. Google Scholar


S. Sasai, T. Kaneko, S. Hasegawa, and K. Tsukamoto . 1999. Morphological alteration in two types of gill chloride cells in Japanese eel (Anguilla japonica) during catadromous migration. Can J Zool 76:1480–1487. Google Scholar


J. I. Scheide and J. A. Zadunaisky . 1988. Effect of atriopeptin II on isolated opercular epithelium of Fundulus heteroclitus. Am J Physiol 254:R27–R32. Google Scholar


C. B. Schreck 1981. Stress and compensation in teleostean fishes: Response to social physical factors. In “Stress and Fish”. Ed by A. D. Pickering Academic Press. New York. pp. 295–321. Google Scholar


A. M. Schreiber and J. L. Specker . 2000. Metamorphosis in the summer flounder, Paralichthys dentatus: thyroidal status influences gill mitochondria-rich cells. Gen Comp Endocrinol 117:238–250. Google Scholar


M. Seidelin and S. S. Madsen . 1999. Endocrine control of Na+,K+-ATPase and chloride cell development in brown trout (Salmo trutta): interaction of insulin-like growth factor-I with prolactin and growth hormone. J Endocrinol 162:127–135. Google Scholar


M. Seidelin, S. S. Madsen, A. Byrialsen, and K. Kristiansen . 1999. Effects of insulin-like growth factor-I and cortisol on Na+,K+-ATPase expression in osmoregulatory tissues of brown trout (Salmo trutta). Gen Comp Endocrinol 113:331–342. Google Scholar


M. Seidelin, S. S. Madsen, H. Blenstrup, and C. K. Tipsmark . 2000. Time-course changes in the expression of Na+,K+-ATPase in gills and pyloric caeca of brown trout (Salmo trutta) during acclimation to seawater. Physiol Biochem Zool 73:446–453. Google Scholar


M. Shapiro, J. Matthews, G. Hecht, C. Delp, and J. L. Madara . 1991. Stabilization of F-actin prevents cAMP-elicited Cl secretion in T84 cells. J Clin Invest 87:1903–1909. Google Scholar


T. Shikano and Y. Fujio . 1998. Relationships of salinity tolerance to immunolocalization of Na+,K+-ATPase in the gill epithelium during seawater and freshwater adaptation of the guppy, Poecilia reticulata. Zool Sci 15:35–41. Google Scholar


N. Shirai and S. Utida . 1970. Development and degeneration of the chlo-ride cell during seawater and freshwater adaptation of the Japanese eel, Anguilla japonica. Z Zellforsch Mikrosk Anat 103:247–64. Google Scholar


K. Shiraishi, J. Hiroi, T. Kaneko, M. Matsuda, T. Hirano, and T. Mori . 2001. in vitro effects of environmental salinity and cortisol on chloride cell differentiation in embryos of Mozambique tilapia, Oreochromis mossambicus, measured using a newly developed ‘yolk-ball’ incubation system. J Exp Biol 204:1883–1888. Google Scholar


K. Shiraishi, T. Kaneko, S. Hasegawa, and T. Hirano . 1997. Development of multicellular complexes of chloride cells in the yolk-sac membrane of tilapia (Oreochromis mossambicus) embryos and larvae in seawater. Cell Tissue Res 288:583–590. Google Scholar


J. M. Shrimpton, R. H. Devlin, E. McLean, J. C. Byatt, E. M. Donaldson, and D. J. Randall . 1995. Increases in gill cytosolic corticosteroid receptor abundance and saltwater tolerance in juvenile coho salmon (Oncorhynchus kisutch) treated with growth hormone and placental lactogen. Gen Comp Endocrinol 98:1–15. Google Scholar


J. M. Shrimpton and S. D. McCormick . 1998. Regulation of gill cytosolic corticosteroid receptors in juvenile Atlantic salmon: interaction effects of growth hormone with prolactin and triiodothyronine. Gen Comp Endocrinol 112:262–274. Google Scholar


M. M. Shull, D. G. Pugh, and J. B. Lingrel . 1990. The human Na, K-ATPase alpha 1 gene: characterization of the 5′-flanking region and identification of a restriction fragment length polymorphism. Genomics 6:451–460. Google Scholar


K. Siharath and H. A. Bern . 1993. The physiology of insulin-like growth factor (IGF) and its binding proteins in teleost fishes. Proc Zool Soc Haldane Commun Vol 1993:113–124. Google Scholar


P. Silva, R. Solomon, K. Spokes, and F. Epstein . 1977. Ouabain inhibition of gill Na-K-ATPase: relationship to active chloride transport. J Exp Zool 199:419–426. Google Scholar


T. D. Singer, S. J. Tucker, W. S. Marshall, and C. F. Higgins . 1998. A divergent CFTR homologue: highly regulated salt transport in the euryha-line teleost F. heteroclitus. Am J Physiol 274:C715–C723. Google Scholar


M. C. Subash Peter, R. A. Lock, and S. E. Wendelaar Bonga . 2000. Evidence for an osmoregulatory role of thyroid hormones in the freshwater mozambique tilapia Oreochromis mossambicus. Gen Comp Endocrinol 120:157–167. Google Scholar


G. Sullivan, J. Fryer, and S. Perry . 1995. Immunolocalization of proton pumps (H+-ATPase) in pavement cells of rainbow trout gill. J Exp Biol 198:2619–2629. Google Scholar


G. V. Sullivan, J. N. Fryer, and S. F. Perry . 1996. Localization of mRNA for proton pump (H+-ATPase) and Cl/HCO3 exchanger in rainbow trout gill. Can J Zool 74:2095–2103. Google Scholar


M. Suzuki, K. Miyazaki, M. Ikeda, Y. Kamaguchi, and O. Sakai . 1993. F-actin network may regulate a Cl channel in renal proximal tubule cells. J Memb Biol 134:31–39. Google Scholar


Y. Suzuki, M. Itakura, M. Kashiwagi, N. Nakamura, T. Matsuki, H. Sakuta, N. Naito, K. Takano, T. Fujita, and S. Hirose . 1999. Identification by differential display of a hypertonicity-inducible inward rectifier potassium channel highly expressed in chloride cells. J Biol Chem 274:11376–11382. Google Scholar


Y. Takei 2000. Structural and functional evolution of the natriuretic peptide system in vertebrates. Int Rev Cytol 194:1–66. Google Scholar


C. K. Tipsmark and S. S. Madsen . 2001. Rapid modulation of Na+/K+ATPase activity in osmoregulatory tissues of a salmonid fish. J Exp Biol 204:701–709. Google Scholar


D. W. Towle, M. E. Gilman, and J. D. Hempel . 1977. Rapid modulation of gill Na++K+-dependent ATPase activity during rapid acclimation of the killifish Fundulus heteroclitus to salinity change. J Exp Zool 202:179–186. Google Scholar


K. Uchida and T. Kaneko . 1996. Enhanced chloride cell turnover in the gills of in chum salmon fry in seawater. Zool Sci 13:655–660. Google Scholar


K. Uchida, T. Kaneko, H. Miyazaki, S. Hasegawa, and T. Hirano . 2000. Excellent salinity tolerance of Mozambique tilapia (Oreochromis mossambicus): elevated chloride cell activity in the branchial and opercular epithelia of the fish adapted to concentrated seawater. Zool Sci 17:149–160. Google Scholar


K. Uchida, T. Kaneko, M. Tagawa, and T. Hirano . 1998. Localization of cortisol receptor in branchial chloride cells in chum salmon fry. Gen Comp Endocrinol 109:175–185. Google Scholar


K. Uchida, T. Kaneko, K. Yamauchi, and T. Hirano . 1996. Morphometrical analysis of chloride cell activity in the gill filaments and lamellae and changes in Na+,K+-ATPase activity during seawater adaptation in chum salmon fry. J Exp Zool 276:193–200. Google Scholar


K. Uchida, T. Kaneko, K. Yamauchi, T. Ogasawara, and T. Hirano . 1997. Reduced hypoosmoregulatory ability and alteration in gill chlo-ride cell distribution in mature chum salmon (Onchorhynchus keta) migrating upstream for spawning. Marine Biol 129:247–253. Google Scholar


A. J. H. Van Der Heijden, P. M. Verbost, J. Eygensteyn, J. Li, S. E. Wendelaar Bonga, and G. Flik . 1997. Mitochondria-rich cells in gills of tilapia (Oreochromis mossambicus) adapted to fresh water or seawater: quantification by confocal laser scanning microscopy. J Exp Biol 200:55–64. Google Scholar


P. J. Walsh 1998. Nitrogen excretion and metabolism. In “The physiology of fishes”. Ed by D. H. Evans CRC Press. Boca Raton. pp. 199–214. Google Scholar


M. Weisbart, P. K. Chakraborti, G. Gallivan, and J. G. Eales . 1987. Dynamics of cortisol receptor activity in the gills of the brook trout, Salvelinus fontinalis, during seawater adaptation. Gen Comp Endocrinol 68:440–448. Google Scholar


S. E. Wendelaar Bonga 1997. The stress response in fish. Physiol Rev 77:591–625. Google Scholar


S. Wendelaar Bonga and C. J. M. van der Meij . 1989. Degeneration and death, by apoptosis and necrosis, of the pavement and chloride cells in the gills of the teleost Oreochromis mossambicus. Cell Tiss Res 255:235–243. Google Scholar


C. F. Weng, T. H. Lee, and P. P. Hwang . 1997. Immune localization of prolactin receptor in the mitochondria-rich cells of the euryhaline teleost (Oreochromis mossambicus) gill. FEBS Lett 405:91–94. Google Scholar


J. M. Wilson, P. Laurent, B. L. Tufts, D. J. Benos, M. Donowitz, A. W. Vogl, and D. J. Randall . 2000a. NaCl uptake by the branchial epithelium in freshwater teleost fish: an immunological approach to ion-transport protein localization. J Exp Biol 203:2279–2296. Google Scholar


J. M. Wilson, D. J. Randall, M. Donowitz, A. W. Vogl, and A. K. Ip . 2000b. Immunolocalization of ion-transport proteins to branchial epithelium mitochondria-rich cells in the mudskipper (Periophthalmodon schlosseri). J Exp Biol 203:2297–2310. Google Scholar


C. K. C. Wong and D. K. O. Chan . 1999. Chloride cell subtypes in the gill epithelium of Japanese eel Anguilla japonica. Am J Physiol 46:R517–R522. Google Scholar


C. M. Wood and W. S. Marshall . 1994. Ion balance, acid-base regulation and chloride cell function in the common killifish, Fundulus heteroclitusa freely euryhaline estuarine teleost. Estuaries 17:34–52. Google Scholar


H. Yasunaga, T. Sakamoto, S. Yokota, and M. Ando . 2001. Differential display of skin mRNAs regulated during adaptation of mudskipper to different environments. J Comp Physiol B in press. Google Scholar


S. Yokota, K. Iwata, Y. Fujii, and M. Ando . 1997. Ion transport across the skin of the mudskipper Periophthalmus modestus. Comp Biochem Physiol 18A:903–910. Google Scholar


G. Young 1988. Enhanced response of the interrenal of coho salmon (Oncorhynchus kisutch) to ACTH after growth hormone treatment in vivo and in vitro. Gen Comp Endocrinol 71:85–92. Google Scholar


G. Young and R. J. Lin . 1988. Response of the interrenal to adrenocortico-tropic hormone after short-term thyroxin treatment of coho salmon (Oncorhynchus kisutch). J Exp Zool 245:53–58. Google Scholar


J. A. Zadunaisky, S. Cardona, L. Au, D. M. Roberts, E. Fisher, B. Lowenstein, E. J. Cragoe Jr, and K. R. Spring . 1995. Chloride transport activation by plasma osmolarity during rapid adaptation to high salinity of Fundulus heteroclitus. J Membr Biol 143:207–217. Google Scholar
Tatsuya Sakamoto, Katsuhisa Uchida, and Shigefumi Yokota "Regulation of the Ion-Transporting Mitochondrion-Rich Cell during Adaptation of Teleost Fishes to Different Salinities," Zoological Science 18(9), 1163-1174, (1 December 2001).
Received: 3 August 2001; Published: 1 December 2001
chloride cell
mitochondrion-rich cell
Back to Top