Elementary events in excitation-contraction coupling of the mammalian myocardium.

Excitation-contraction coupling of the mammalian myocardium is widely assumed to comprise the following chain of events: (1) Influx of Ca++ into the cell during the plateau phase of the action potential as well as Ca++ release from the subsarcolemmal cisternae of sarcoplasmic reticulum. (2) Activation of the contractile proteins by interaction of Ca++ with the troponin-tropomyosin system. (3) Relaxation due to reuptake of Ca++ by the sarcotubular system as well as by pumping of Ca++ out of the cell through the surface membrane and the transverse tubular system. (4) Movement of Ca++ in the longitudinal tubules back to the subsarcolemmal cisternae. A short comment is included about the effects of hypertrophy on the excitatory processes as well as on cellular structural constituents directly involved in excitation-contraction coupling.