Calcium-Permeable Channel in Sarcoplasmic Reticolum of Rabbit Skeletal Muscle

Membrane vesicles from sarcoplasmic reticulum of rabbit skeletal muscle were incorporated into a bilayer lipid membrane. With this system, single current fluc-tuation was observed in the presence of 50 mM Ba-gluconate. This channel activity was observed only in vesicles from terminal cisternae. The single channel conduc-tance was 14.1 pS, and the channel state was almost wholly open. The open-close transition of the channel obeyed simple two-state kinetics and was voltage-independ-ent. The ionic selectivity was also studied, and the channel showed no selectivity among Ba, Ca, Mn, and Mg. On the other hand, it was less permeable to Cs than to Ba. Based on these results, the relation of the Ca channel to excitation-contrac-tion coupling is discussed. The excitation-contraction coupling (E-C coupling) begins with excitation of the sarcolemma. It prop-agates to the transverse tubule (T-tubule) mem-brane and then to the sarcoplasmic reticulum (SR). SR supplies calcium, which regulates muscle con-traction. Thus, calcium release from SR is an important step in E-C coupling. In spite of many studies, the mechanism of information transmission from T-tubules to SR (T-SR coupling) has not been clarified. It is certain that charge movement oc-curs in the T-tubule membrane accompanied with the excitation of T-tubules (/). Based on thes