Membrane Excitation in Cardiac Muscle

Abstract

The contributions made during the past 10 years are reviewed. Intracellular recording has made it possible to state absolute values for the cardiac resting potential (90 mv., inside negative to outside) and the "overshoot" during activity (30 mv., inside positive to outside). The surface membrane of a resting fiber is considered to be predominately permeable to K ions. During activity, Na conductance increases and K conductance decreases. The latter process is thought to be essential for explaining the high membrane resistance that is measured during the long-lasting "plateau" found with cardiac muscle. A hypothesis is presented that would account for the termination of the plateau and the beginning of repolarization.