Effects of hypokalemia on the cardiotropic actions of digoxin in dogs. Correlation with inhibition of cardiac Na+,K+-adenosine triphosphatase.

Hypokalemia potentiated the arryhthmogenic effects of digoxin and promoted inhibition of cardiac Na+,K+-ATPase. Acute hypokalemia did not modify digoxin-induced inotropy and therefore altered the quantitative relationship between inhibition of Na+,K+-ATPase and positive inotropy. Chronic hypokalemia impaired the positive inotropic response to digoxin and to isoproterenol in the absence of an electron microscopically detectable cardiomyopathy.