THE EFFECT OF THE IONIC MILIEU ON THE RESPONSE OF RABBIT CARDIAC MUSCLE TO OUABAIN

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

The effects of changing the calcium, potassium or sodium concentration in Tyrode's solution on the positive inotropic and toxic effects of ouabain have been studied. High calcium, low potassium or sodium, or high potassium or sodium reduced the positive inotropic effects of ouabain. Effects of high calcium concentrations could not be reversed by increasing either sodium or potassium concentrations. The effects of high potassium could be partially reversed by an increase in the sodium chloride concentrations. The inhibition produced by high sodium concentrations could be partially reversed by increasing the potassium but not by increasing the calcium concentration. Rubidium chloride can partially substitute, while lithium, cesium, choline, tetraethylammonium and ammonium ion cannot substitute, for potassium chloride in the production of the positive inotropic effect of ouabain. Reduction of sodium chloride concentration which reduced the positive inotropic response to ouabain can be partially substituted for by choline chloride but not by lithium chloride. These results are correlated with those obtained by others on the isolated ion-activated membrane adenosine triphosphatase. Qualitative positive correlations have been discussed.