Comparison of [3H]ouabain binding sites in intact cells and cell homogenates: apparent lack of glycoside receptors unrelated to sarcolemmal Na+, K+-ATPase in guinea-pig heart.

In intact heart muscle cells incubated in a physiological solution, i.e. under the condition in which the cardiac glycosides produce pharmacological and toxicological effects, receptors for these actions of the glycosides should be available to ouabain. In cell homogenates, [3H]ouabain binding observed in the presence of Mg2+ and inorganic phosphate represents binding of the glycoside to Na+, K+-ATPase. Therefore, numbers of these two types of [3H]ouabain binding sites were compared using viable myocyte preparations obtained from ventricular muscle of guinea-pig heart. The number of ouabain binding sites observed in viable myocytes in the absence of Ca2+ and K+ was not different from the number of ouabain binding sites on Na+, K+-ATPase observed with sodium dodecylsulfate-treated homogenates prepared from isolated myocytes. These results do not support the hypothesis that there are receptors for the pharmacological or toxic actions of ouabain other than those that are associated with sarcolemmal Na+, K+-ATPase.