Cell membrane responsiveness and excitation-contraction coupling in smooth muscle

In this study of the excitation-contraction coupling in arterial smooth-muscle cells, the relations between changes of the membrane potential, force development, and 45Ca exchange have been investigated. It is proposed that the cell membrane plays a primary role by regulating the Ca entry into smooth-muscle cells and by extruding the excess cytoplasmic Ca. The possible relation between the receptor-operated channels and the sarcoplasmic reticulum has been discussed, and the peculiar differences between exogenous noradrenaline and noradrenaline released from the nerve terminals have been described.