A STUDY ON THE EFFECT OF CARDIAC GLYCOSIDES ON THE SYNERESIS OF MYOFIBRILS IN THE PRESENCE OF RELAXING FACTOR

¹ Department of Pharmacology, State University of New York, Downstate Medical Center, Brooklyn, New York

The relaxing factor isolated from the skeletal and heart muscle was found to inhibit the syneresis of myofibrils and to take up Ca⁺⁺ actively from the surrounding medium. The cardiac glycosides, strophanthin K and digitoxin, did not influence these functions of RF. The passage of electrical impulses (1.5-2 volts, 60/min, 10 msec) through mixtures containing RF and myofibrils for a 2-minute incubation period, reversed the inhibitory effect of RF on the syneresis of myofibrils. However, when the voltage or frequency of electrical stimulation was decreased, the reversal effect of the stimulation was markedly reduced. The cardiac glycosides were found to potentiate the reversal effect of the electrical stimulation when the latter was insufficient to cause the complete syneresis of myofibrils. The site of effect of both the electrical stimulation and the cardiac glycosides appeared to reside at the relaxing factor.