Effect of stretching on the action potentials of the human and rabbit ventricular myocardium

: The effect of stretching from L0 to Lmax on the electrical activity was studied on human myocardial preparations from patients with heart disease and on strips of rabbit ventricular myocardium. Muscular deformation was shown to decrease the amplitude and velocity of depolarization in slow action potentials. The action potentials (AP) possessing a fast depolarization phase were not sensitive to physiological stretching. Antiarrhythmic drugs--ethmozin (2 X 10(-5) M) and ethacizin (2 X 10(-6) M)--caused a decrease in the rate of AP depolarization, thus increasing AP sensitivity to deformation. It is suggested that stretching under the action of ethmozin and ethacizin reduced cardiomyocyte excitability due to suppression of slow Ca-current.