A MATHEMATICAL ANALYSIS OF THE INTERVAL-STRENGTH RELATIONSHIP IN THE RAT VENTRICLE STRIP AND ITS MODIFICATION BY FLUOROACETATE

¹ Department of Pharmacology, University of Southern California, School of Medicine, Los Angeles, California

The recovery of contractility after a rested-state contraction and the cumulation and disappearance of potentiation in the rat ventricle strip have been studied. The time course of the recovery of contractility was found to proceed in two phases and was described by a solution of a second-order differential equation. The cumulation of potentiation followed first-order kinetics whereas the disappearance of potentiation consisted of two components whose time course was given by a solution of a second-order differential equation. Fluoroacetate stimulated the rested-state contraction. The positive inotropic effect was greater in reduced calcium medium. The inhibitor exerted a marked acceleration of the first phase of recovery of contractility. The effect of fluoroacetate on potentiation was complex. The magnitude of potentiation was inhibited. The rate of the cumulation and of the first phase of the disappearance of potentiation decreased progressively while that of the second phase decreased after an initial lag. During the positive inotropic effect of fluoroacetate the time to peak tension in an individual rested-state contraction decreased and the maximum rates of contraction and relaxation increased.