THE EFFECT OF OUABAIN ON THE FREQUENCY-FORCE RELATION AND ON POST-STIMULATION POTENTIATION IN ISOLATED ATRIAL AND VENTRICULAR MUSCLE

¹ Department of Pharmacology, State University of New York, Upstate Medical Center, Syracuse, New York

The frequency-force curve and post-stimulation potentiation are intrinsic properties of myocardial muscle. Conditions which produce a depression of contractility also abolish the frequency-force relationships.

The effect of cardioactive glycosides on the frequency-force relationships is dependent upon the drug concentration. Concentrations which increase contractility at physiological heart rates potentiate the frequency-force curve and post-stimulation potentiation. Higher concentrations of the glycosides first increase and later decrease tension at low, unphysiological heart rates and abolish the frequency-force relationships.

In depressed myocardial muscle "therapeutic" concentrations of the cardioactive glycosides may re-establish the frequency-force curve and increase post-stimulation potentiation.

It is suggested that the cardioactive glycosides produce their therapeutic, positive inotropic effect by acting on the frequency-dependent potentiating mechanism of myocardium.