Membrane ion channel activation

The SR may contribute to excitation-contraction (EC) coupling in two ways firstly, by the release of Ca2+ for contraction as described above, but secondly by modulating membrane excitability. As will be described elsewhere in this book, the SR is an important mediator of surface membrane ion channel activity, and hence, excitability. Spontaneous Ca2+ release from the SR can activate Ca2+-sensitive ion channels. Both K+ (Kca) and Cl- (Clsmooth muscle cell membrane can be activated by SR Ca2+. If Kca channels are activated there will be a hyperpolarization, as K+ ions leave the cell and spontaneous transient outward currents (STOCs) can be recorded (Carl et al 1996, Nelson Quayle... 

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