Iwamoto H, Suzuki S, Mizobe H
Department of Physiology, School of Medicine, Teikyo University, Japan.
Cell Tissue Res. 1988 Jul;253(1):15-21. doi: 10.1007/BF00221734.
Regulatory mechanism of contraction in the proboscis retractor muscle of Phascolosoma scolops was studied by physiological measurements and cytochemical electron microscopy. The magnitude of K+-contracture was dependent on external Ca2+ concentration and the contracture disappeared in Ca2+-free solution. The K+-contracture was suppressed by application of procaine and Mn2+. Caffeine induced contracture even when external Ca2+ was absent. Ultrastructural observations of the retractor muscle cells showed the presence of a large number of vesicles (subsarcolemmal vesicles), corresponding to the sarcoplasmic reticulum in vertebrate skeletal muscle, underneath the plasma membrane. For the cytochemical electron microscopy, the muscle fibers were fixed with 1% OsO4 solution containing 2% K-pyroantimonate. In the relaxed fibers, pyroantimonate precipitates were localized along the inner surface of plasma membrane and in the subsarcolemmal vesicles. In the contracting fibers, the precipitates were uniformly distributed in the myoplasm. The X-ray microanalysis revealed that the precipitates contained Ca. These results suggest that the contractile system is activated by the influx of extracellular Ca2+ as well as by the release of Ca2+ from the intracellular structures such as the inner surface of the plasma membrane and subsarcolemmal vesicles.
通过生理学测量和细胞化学电子显微镜研究了扁玉螺吻缩肌收缩的调节机制。钾离子挛缩的程度取决于细胞外钙离子浓度，且在无钙溶液中挛缩消失。钾离子挛缩可被普鲁卡因和锰离子抑制。即使细胞外没有钙离子，咖啡因也能诱导挛缩。对缩肌细胞的超微结构观察显示，在质膜下方存在大量小泡（肌膜下小泡），这与脊椎动物骨骼肌中的肌浆网相对应。对于细胞化学电子显微镜，肌纤维用含有2%焦锑酸钾的1%四氧化锇溶液固定。在松弛的纤维中，焦锑酸盐沉淀定位于质膜内表面和肌膜下小泡中。在收缩的纤维中，沉淀物均匀分布在肌浆中。X射线微分析显示沉淀物含有钙。这些结果表明，收缩系统是由细胞外钙离子的流入以及细胞内结构（如质膜内表面和肌膜下小泡）中钙离子的释放激活的。
