CONTINUITY OF THE T SYSTEM WITH THE SARCOLEMMA IN RAT SKELETAL MUSCLE FIBERS

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Abstract
Electron microscope examination of gastrocnemius muscle fibers shows that the continuity between the sarcolemma and the T system is formed near the junctions of the A and I bands by invagination of the sarcolemma. The extracellular fluid is continuous with the tubular content of the T system. Between the apposed membranes of the T system and the terminal segments of the sarcoplasmic reticulum is a 100 A wide space. Dense zones of electron opacity across this space suggest the presence of connections between the apposed membranes of the T system and the sarco-plasmic reticulum. Intermembranous connections, rather than anatomical tight junctions, may form an integral part of apposition of T system and sarcoplasmic reticulum membranes.