Molecular Pharmacology, Vol 17, 61-65, Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics

The Modification of Unidirectional Calcium Fluxes by Dibucaine in Sarcoplasmic Reticulum Vesicles from Rabbit Fast Skeletal Muscle

¹ Division of Cardiology, Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut 06032

The ability of dibucaine to modify unidirectional calcium fluxes was studied in sarcoplasmic reticulum vesicles prepared from rabbit fast skeletal muscle. Dibucaine inhibited initial calcium uptake velocity in a concentration-dependent manner; at 7.4 µM Ca²⁺, approximately 0.8 mM dibucaine was required to achieve half-maximal inhibition of the calcium pump. This inhibitory effect of dibucaine was increased when external Ca²⁺ was decreased. Lower dibucaine concentrations (0.08-0.64 mM), however, stimulated calcium uptake when added to calcium-filled vesicles. This stimulatory effect of dibucaine was due to a decrease in the calcium efflux rate of the vesicles. Higher dibucaine concentrations (>0.9 mM) increased calcium efflux and inhibited calcium influx when added to calcium-filled vesicles. These complex effects of dibucaine on calcium transport by the sarcoplasmic reticulum may reflect the ability of this drug to stabilize the membrane at lower concentrations and to disrupt or induce lysis of the membrane at higher concentrations.

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