MOLECULAR EVOLUTION OF SKELETAL MUSCLE E-C COUPLING

我们从系统发育的角度探讨了骨骼肌兴奋-收缩耦合的分子机制。骨骼肌E-C偶联的特点是由t管膜上的电荷运动直接触发细胞内Ca^<2+>从肌浆网释放，因此E-C偶联不需要外部Ca^<2+>的内流。(1)在仅缺乏骨骼肌E-C偶联的肌肉发育不良（MDG）突变小鼠中。一种被硝苯地平固定的电荷成分（Q_< δ >）在它们的骨骼肌细胞中缺失，而在正常小鼠的骨骼肌细胞中存在。(2)在无脊椎动物的快抽动肌中，E-C耦合绝对需要外源Ca^<2+>的内流。因此，我们认为获得骨骼肌型E-C偶联的进化发生在动物进化的某个阶段。我们发现在头脊索动物和agnathan（最早的……更多的脊椎动物）之间的进化步骤是离散的。这一演化过程伴随着Q_< δ >的出现。(3)前脊椎动物横纹肌的许多结构变异对未来获得新型E-C耦合具有重要意义。在矢状鼠中，虽然t小管和SR都存在，但咖啡因或瑞诺定对细胞内Ca^<2+>的释放没有影响。在阑尾，Oikopleuxa， t小管和SR都存在，咖啡因诱导和ryanodine阻断Ca^<2+>从SR释放，但Co^<2+>阻断E-C耦合，表明Ga^<2+>内流是必要的。在蓟马属植物中，t小管和SR都不存在，因此咖啡因或瑞诺定没有作用。在头脊索类、文文鱼中，没有t小管但有SR存在，咖啡因、瑞诺定和Co^<2+ bbb24有其特定的作用。在这些动物中，细胞内Ca^<2+>的调节机制逐渐进化。(4)我们发现获得电压传感器的分子进化可能在胎鼠骨骼肌形成早期重复进行。(5)将MDG细胞系引入日本，建立了DHP-受体亚型表达检测体系。少

We have been investigating the molecular mechanisms in skeletal muscle excitation-contraction coupling on the aspect of phylogeny. Skeletal muscle E-C coupling is characterized by direct triggering by charge movement in the T-tubular membrane of intracellular Ca^<2+> release from the sarcoplasmic reticulum, hence influx of external Ca^<2+> is not required in the E-C coupling.(1)In mutant mice with muscular dysgenesis (MDG) that lack only skeletal muscle E-C coupling. a component of charge (Q_<delta>) which is specifically immobilized by nifedipine is found to be absent in their skeletal muscle cells, whereas it is present in those of normal mice.(2)In fast twitch muscle of invertebrate, E-C coupling absolutely requires influx of external Ca^<2+>.It is therefore suggested that evolution to acquire skeletal muscle type E-C coupling occurred somewhere during animal evolution. We found that the evolutionary step occurred in adiscrete manner between cephalochordate and agnathan (the earlies … More t vertebrate). This evolutionary step is found to be accompanied by the appearance of Q_<delta>.(3)There are many structural variations of striated muscle in pre-vertebrates toward the future acquirement of novel E-C coupling. In the cataegnatha, Sagitta, although both T-tubules and SR are present, caffeine or ryanodine has no effect on intracellular Ca^<2+> release. In the appencliculata, Oikopleuxa, both T-tubules and SR are present, caffeine induces and ryanodine blocks Ca^<2+> release from SR but Co^<2+> blocks E-C coupling indicating Ga^<2+> influx is necessary. In the thraliacea, Doliolum, both T-tubules and SR are absent, hence caffeine or ryanodine has no effect. In the cephalochordata, amphioxus, no T-tubUles but SR is present, caffeine, ryanodine, and Co^<2+>24 have their specific effects. In there animals, there is a gradual evolution of regulation mechanisms of intracellular Ca^<2+>.(4)We found that the molecular evolution to acquire the voltage sensor may be repeated in the early stage of skeletal myogenesis in fetal mice.(5)We have brought the MDG ell line into Japan, and established the system of examining expression of DHP- receptor subtypes. Less