The role of intracellular sodium ions in the regulation of cardiac contractility

Abstract

It has been known for a long time that the contractility of cardiac muscle depends on the pattern of stimulation [ 2, 3, 15], but the underlying mechanisms are still a matter of controversy [ 14]. Here I wish to present experimental evidence that both the “positive inotropic effect of activation” (PIEA) [ 2] and the positive inotropic effect of cardiac glycosides may be the result of a change in intracellular sodium activity. This conclusion is based on the direct measurement of the time course of (i) the blockage of the electrogenic pump current by a fast acting cardiac glycoside, dihydro-ouabain, (ii) the resulting change in intracellular sodium activity, (iii) the accompanying change in contractility, and (iv) the decay of the PIEA in guinea-pig ventricular muscle.