INTERACTION OF HYDRALAZINE WITH TENSION DEVELOPMENT AND MECHANISMS OF CALCIUM ACCUMULATION IN K plus -STIMULATED RABBIT AORTIC STRIPS

Abstract

The effects of hydralazine on K+ contractures in rabbit aortic strips was studied. Measurements were made of effects on tension generation, Ca2+ accumulation measured using 45Ca2+ (La method) and 45Ca2+ efflux. Hydralazine relaxed established K+ contractures and inhibited tension development when tissue exposure to hydralazine preceded K+ depolarization. Threshold and maximum tension responses of strips to Ca2+ (K+-depolarized tissues) were altered by hydralazine in a dose-dependent manner. The Ca2+ uptake associated with K+ depolarization was inhibited by relaxant doses of hydralazine, hydralazine did not significantly affect the rate of 45Ca2+ efflux. Hydralazine also raised the threshold to the inhibitory (relaxant) effects of higher (> 2.5 mM) bath concentrations of Ca2+. Hydralazine may inhibit K+ contractures in aortic strips by interference with the entry of Ca2+ into the cell, reflecting an effect of hydralazine at the cell surface membrane.