Effects of Specific 3-H-Ouabain Binding to the Cardiac Glycoside Receptor on (Na + +K + )-ATPase Activity and on Force of Contraction in Rat Heart

The exact mechanism of action of cardiac glycosides (CG) is not known. Several investigations have revealed that upon binding of CG to a specific membrane-bound receptor the also membrane-bound (Na++ K+)-ATPase is inhibited. This inhibition is supposed to be necessary for the positive inotropic effect of CG. This hypothesis is not unchallenged. We therefore measured at identical conditions in rat heart preparations: 3-H-ouabain binding to isolated cell membranes and to electrically stimulated contracting ventricular strips (ouabain concentration 10−9-10−4M), (Na++ K+)-ATPase activity, and contractile force. The time courses of the CG-effects were recorded, too.