Relationship between myocardial K+ balance, O2 consumption, and contractility

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Abstract
Nine types of interventions which changed ventricular contractility were made in the isolated supported heart preparation. Three of these were hemodynamic interventions, 6 were pharmacologic. In 7 of these 9 interventions, when contractility increased there was a net loss of K+ from the heart and when contractility decreased there was a net gain of K+. Special attention was given to K+ changes during pressure-induced homeometric autoregulation and after acetyl strophanthidin. There was a net K+ loss in 19 of 22 experiments during pressure-induced homeometric autoregulation. The amount of the net K+ loss appeared to vary with the observed increase in 02 consumption especially when serial observations were made in the same heart. With acetyl strophanthidin, both the increase in contractility and the net K+ loss varied with the dose given, thus indicating a relation between amount of the net K+ loss and the contractility increase. It was demonstrated that contractility would decrease during an intra-coronary infusion of K+ when the heart had taken up amounts of K+ comparable in magnitude to the losses observed during homeometric autoregulation or acetyl strophanthidin. Speculative hypotheses are presented linking K+ changes to changes in contractility and also certain other possible mechanisms.