The current concept for the cardiac glycoside receptor.

This brief review emphasizes the significance of the Na+,K+-ATPase or the Na+,K+ pump of the intact membrane as the pharmacological receptor for cardiac glycosides. The properties of transport enzyme and the regulation of glycoside binding are described. An outline is given of the problems encountered and of the progress made in attempting to correlate the inotropic action of cardiac glycosides with the binding of these drugs to the heart muscle and with the inhibition of the Na+,K+ pump. Furthermore, the correlation of intracellular Ca2+ activity an Na+ concentration with the inhibition of the Na+,K+ pump is discussed. The existence of a digitalis-like endogenous activity may also indicate an important role of the Na+,K+ pump as a receptor for a physiological regulatory control of cardiac contractility.