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1 March 2003 Amino Acid-Permeable Anion Channels in Early Mouse Embryos and Their Possible Effects on Cleavage
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Effects of several Cl channel blockers on ionic currents in mouse embryos were studied using whole-cell patch-clamp and microelectrode methods. Microelectrode measurements showed that the resting membrane potential of early embryonic cells (1-cell stage) was −23 mV and that reduction of extracellular Cl concentration depolarized the membrane, suggesting that Cl conductance is a major contributor for establishing the resting membrane potential. Membrane currents recorded by whole-cell voltage clamp showed outward rectification and confirmed that a major component of these embryonic currents are carried by Cl ions. A Cl channel blocker, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), suppressed the outward rectifier current in a voltage- and concentration-dependent manner. Other Cl channel blockers (5-nitro-2-[3-phenylpropyl-amino] benzoic acid and 2-[3-(trifluoromethyl)-anilino] nicotinic acid [niflumic acid]) similarly inhibited this current. Simultaneous application of niflumic acid with DIDS further suppressed the outward rectifier current. Under high osmotic condition, niflumic acid, but not DIDS, inhibited the Clcurrent, suggesting the presence of two types of Cl channels: a DIDS-sensitive (swelling-activated) channel, and a DIDS-insensitive (niflumic acid-sensitive) Cl channel. Anion permeability of the DIDS-insensitive Cl current differed from that of the compound Cl current: Rank order of anion permeability of the DIDS-sensitive Cl channels was I = Br > Cl > gluconate, whereas that of the DIDS-insensitive Cl channel was I = Br > Cl ≫ gluconate. These results indicate that early mouse embryos have a Cl channel that is highly permeable to amino acids, which may regulate intracellular amino acid concentration.

Momoyo Sonoda, Fujio Okamoto, Hiroshi Kajiya, Yoshihito Inoue, Ko Honjo, Yoshinari Sumii, Tatsuhiko Kawarabayashi, and Koji Okabe "Amino Acid-Permeable Anion Channels in Early Mouse Embryos and Their Possible Effects on Cleavage," Biology of Reproduction 68(3), 947-953, (1 March 2003).
Received: 19 June 2002; Accepted: 1 October 2002; Published: 1 March 2003

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