Franzini-Armstrong C
Fed Proc. 1975 Apr;34(5):1382-9.
The structure of the membranes limiting the sarcoplasmic reticulum (SR) and transverse (T) tubules in frog and fish muscle fibers has been studied by freeze fracture. Emphasis is placed on the structure of the membranes at the triad, where thin sections have previously shown that rows of regularly disposed "feet" join SR and T exposed fracture faces allows the following conclusions. 1) The SR membrane is continuous and identical in appearance along the whole sarcomere. Thus the SR is a single uninterrupted compartment and it is likely that the major function of the reticulum, calcium accumulation is performed by the membrane limiting the lateral sacs of the triad, as well as the longitudinal tubules. 2) At the level of the junction with the T tublue, the SR presents a strikingly different number, size and arrangement of particles and pits. This distinct portion of the SR membrane extends father than the area covered by the junctional "feet" and no correlation can be found between the disposition of particles within the membrane and that of the feet on the membrane surface. 3) The T system membrane presents few prominent particles on its junctional face, but these are far less numerous than the feet. 4) Thus, no visible preformed channels exist between SR and T system lumina and it is suggested that direct electrical coupling between the two membranes during excitation is unlikely.
利用冷冻蚀刻技术研究了青蛙和鱼类肌肉纤维中限制肌浆网（SR）和横管（T管）的膜结构。重点研究了三联体处的膜结构，此前的超薄切片显示，成行排列的规则“足”连接着SR和T管。蚀刻后的断裂面得出以下结论：1）SR膜在整个肌节中外观连续且相同。因此，SR是一个单一的连续区室，网状结构的主要功能——钙积累，很可能是由限制三联体侧囊以及纵向小管的膜来执行的。2）在与T管的连接处，SR呈现出明显不同的颗粒和凹坑数量、大小及排列。SR膜的这一独特部分延伸的范围比连接“足”覆盖的区域更远，且膜内颗粒的分布与膜表面“足”的分布之间没有相关性。3）T系统膜在其连接面上有一些突出的颗粒，但数量远少于“足”。4）因此，SR和T系统管腔之间不存在可见的预制通道，这表明在兴奋过程中，两个膜之间不太可能存在直接的电偶联。
