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1 August 2005 Sources of Activator Calcium Ions in the Contraction of Smooth Muscles in Aplysia kurodai
Zhenli Huang, Yoshiki Ishii, Takashi Watari, Han Liu, Shin-ichi Miyake, Toshinobu Suzaki, Teizo Tsuchiya
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Abstract

The physiological and pharmacological properties of contraction and the ultrastructure of buccal mass retractor muscle (I4) and gill-pinnule closure muscle (GPCM) in Aplysia kurodai were studied to learn more about the sources of activator Ca2 in molluscan smooth muscle. Acetylcholine (ACh) and high K -induced contractions were reduced by lowering the external Ca2 concentration, and eliminated by the removal of extracellular Ca2 . Nifedipine appreciably reduced ACh- and high K -induced contractions, while amiloride decreased only ACh-induced contractions and had no significant effect on high K -induced contractions. When nifedipine and amiloride were applied together, either type of contraction was still appreciable. Serotonin (5-HT) could potentiate subsequent ACh- and high K -induced contractions in I4; potentiated tension was significantly reduced by nifedipine and amiloride, whereas 5-HT inhibited ACh- and high K -induced contractions in GPCM. The potentiating effects of 5-HT may be mediated by the activation of the Ca2 -channel to increase the influx from extracellular Ca2 . Caffeine caused contractions in Ca2 -free solution in both muscles. Electron microscopy revealed sarcolemmal vesicles underneath the plasma membrane in both muscle fibers. Electron microscopical cytochemistry demonstrated that pyroantimonate precipitates were localized in the sarcolemmal vesicles and in the inner surface of plasma membranes in the resting fibers. Present results indicate that the contractions of I4 and GPCM fibers are caused not only by Ca2 -influx but also by Ca2 release from the intracellular storage sites, such as the sarcolem-mal vesicles and the inner surface of plasma membranes.

Zhenli Huang, Yoshiki Ishii, Takashi Watari, Han Liu, Shin-ichi Miyake, Toshinobu Suzaki, and Teizo Tsuchiya "Sources of Activator Calcium Ions in the Contraction of Smooth Muscles in Aplysia kurodai," Zoological Science 22(8), 923-932, (1 August 2005). https://doi.org/10.2108/zsj.22.923
Received: 1 February 2005; Accepted: 1 May 2005; Published: 1 August 2005
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