CALCIUM MOBILIZATION BY CADMIUM OR DECREASING EXTRACELLULAR NA+ OR PH IN CORONARY ENDOTHELIAL-CELLS

Replacing extracellular Na+ with choline transiently increased cytoplasmic free Ca2+ ([Ca2+]i) more than 5-fold in coronary endothelial cells. Removing external Na+ stimulated 45Ca2+ efflux ~4-fold and influx ~1.7-fold. The stimulation of efflux was independent of extracellular Ca2+ and the osmotic Na+ substitute. The release of stored Ca2+, rather than Ca2+ influx via Na+Ca2+ exchange, probably causes the increase in [Ca2+]i and 45Ca2+ efflux. Cadmium or decreasing external, not intracellular, pH transiently increased [Ca2+]i. Cd2+ and some other divalent metals also stimulated 45Ca2+ efflux. The potency order of the metals that stimulated efflux was Cd2+ > Co2+ > Ni2+ > Fe2+ > Mn2+. Incubating the cells with Zn2+ prior to assaying efflux in the absence of Zn2+ strongly inhibited the stimulation of 45Ca2+ efflux by Cd2+, pH 6, and the removal of external Na+ without affecting the stimulation of efflux by ATP. These findings support the hypothesis that certain trace metals or decreasing external Na+ or pH trigger the release of stored Ca2+ by stimulating a cell surface "receptor.". © 1991.