Ouabain Effects on Cardiac Contraction, Action Potential, and Cellular Potassium

Transmembrane potential, isometric tension, and K 42 content of sheep or calf myocardial bundles were recorded simultaneously during periods up to 30 hours. Ouabain at low concentrations (1.5 x 10 -8 M/L) decreased intracellular K to a new steady level which was reached after several hours. Its value depended on drug concentration. The effect was reversible. There was a striking temporal parallelism between the potassium loss and the inotropic effect which was suggestive of a close relationship between the two phenomena. Action potentials during these experiments did not change in a consistent way.