Myocardial sarcolemmal ATPase in dogs with induced mitral insufficiency.

A study of the sarcolemmal Na+K+ATPase in the left failing heart due to induced mitral insufficiency was made in dogs. The sarcolemmal Na+K+ATPase markedly increased in the failing left ventricle. There was no change in the ATPase in the nonfailing right ventricle of the same dog. It was observed that during the early period of mitral incompetence, when there was an increase in the index of myocardial contractility, there was also a decrease in the sarcolemmal Na+K+-ATPase activity. There was no change in the MPG++-ATPase of the sarcolemmal fractions of either the failing or nonfailing ventricle. These results indicate that sarcolemmal Na+K+-ATPase appears to be involved in the reduction of the myocardial contractility during heart failure.