The relation between the action potential duration, the increase in resting tension, and ATP content during metabolic inhibition in guinea pig ventricular muscles.

Abstract

To investigate whether the action potential duration (APD) or resting tension was dependent on global ATP content, and whether they were preferentially dependent on glycolytic ATP, APD and resting tension were measured under various metabolic inhibition with corresponding measurement of ATP content in guinea pig ventricular muscles. Oxidative phosphorylation was inhibited by either hypoxic perfusion, the perfusion of sodium cyanide, or 2,4-dinitrophenol. Glycolysis was blocked by the perfusion of iodoacetic acid, and hypoxia with variable glycolytic activities was achieved by hypoxic perfusion in the presence of glucose (5, 10, and 50 mM). APD began to decrease when ATP content decreased to less than 3 mM/kg w.w. from the control level of 4.35 mM/kg w.w. APD shortened significantly and resting tension increased steeply, when ATP content decreased below 1 mM/kg w.w. The dependence of APD and the increase in resting tension on ATP content was not affected by the mode of metabolic block, that is, the inhibition of glycolysis and/or oxidative phosphorylation. Though other factors can affect APD and resting tension, we found no evidence of functional ATP compartmentation, with respect to APD and the increase in resting tension during metabolic inhibition.