ELECTRICAL MEMBRANE ACTIVITY AND FREQUENCY-FORCE RELATIONS IN NORMAL, DENERVATED AND RESERPINE-PRETREATED CAT HEART MUSCLE

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

Transmembrane potentials and contractile activity were recorded simultaneously in isolated spontaneously beating atria and in electrically driven left atria and right ventricular strips of the cat. Catecholamine depletion by sympathetic denervation or by reserpine pretreatment produced no significant differences in electrophysiologic parameters or basal contractile activity. Carbamylcholine reduced atrial cell action potential duration but had no effect on action potentials of normal ventricle. Action potentials of denervated and reserpine-pretreated ventricles were usually prolonged by carbamyicholine. Atropine blocked the prolongation. The frequency-force curves for denervated and reserpine-pretreated left atria at 38°C differ from those of normal atria. At 27°C, the frequency-force curves were similar for normal and catecholamine-depleted atria. After carbamyicholine, the frequency-force curves of normal, denervated and reserpinepretreated left atria at 38°C all demonstrated a decline in tension as the frequency of stimulation increased. No significant differences were observed in the frequency-force curves of normal, denervated and reserpine-pretreated right ventricular strips. Poststimulation and postquiescent potentiation did not differ among normal, denervated and reserpinepretreated atria or ventricles. The data indicate that endogenous catecholamines do not play any significant role in the electrical or mechanical integrity of cardiac muscle.