The link between skeletal and smooth muscle : Evolution of E-C coupling factor

在这项研究中，我用海洋动物研究了将平滑肌转化为骨骼肌的连接因素。海洋动物有许多控制肌肉细胞收缩的细胞器组合，即肌浆网(SR)、横管结构(T系统)、钙通道、兰诺定受体和DHP受体。另一方面，有SR但没有T系统的海鞘肌肉需要细胞外钙来收缩，通常表现为平滑肌肉。但通过向SCN添加咖啡因或取代外部氯，心肌在缺乏外部钙的情况下会像骨骼肌一样收缩。另一方面，在缺乏外部钙的情况下，心肌像骨骼肌一样，通过电刺激收缩在缺乏T细胞器和SR细胞器的浮游生物上，即使有咖啡因存在，肌肉也只能在外加钙的存在下收缩。提示SR的存在是骨骼肌型收缩所必需的，即使不活跃，SR上也存在E-C偶联因子。偶联因子可能存在于平滑肌SR中，但偶联可能非常松散。通过发展这种偶联，可以将平滑肌转化为骨骼肌。

In this study, I have investigated the link factor which converts the smooth muscle to the skeletal muscle using marine animals.Marine animals have a large varieties of combinations of organelles, which control the contraction of the muscle cells, i. e., sarcoplasmic reticulum (SR), transvers tubular structure (T system), Ca channel, ryanodine receptor and DHP receptor.Heart muscles of Ascidia Ciona, which has SR but not T system, requires extracellular Ca for its contraction and usually behaves like smooth muscle.But by adding caffeine or replacing external Cl to SCN, heart muscle contracted by electrical stimulations in the absence of external Ca like skeletal muscle.On the other hand, on pelagic tunicate Doliolum, which lacks T and SR organelles, muscle contracted only in the presence of external Ca, even if caffeine was present.It is suggested that the presence of SR is essential for skeletal muscle type contraction and the E-C coupling factor exist on SR even if it is not active.The coupling factor suggested to be existed in smooth muscle SR but the coupling might be very loose.By developing the coupling, smooth muscle maight be converted to skeletal muscle.