Evidence for a Direct Inhibitory Effect of Extracellular H+on Store Depletion-Activated Ca2+Entry in Vascular Endothelial Cells

Abstract

Modulation of store depletion-activated Ca2+entry by acidosis was investigated in ECV304 endothelial cells. Lowering extracellular pH from 7.4 to 6.9 markedly suppressed Ca2+entry elicited by direct depletion of Ca2+stores with thapsigargin (100 nM), but did not significantly affect leak Ca2+entry. Acidosis diminished thapsigargin-induced Ca2+entry by 53.7 ± 7.8% at 2.5 mM extracellular Ca2+. A similar degree of inhibition was observed in cells depolarized by high extracellular K+(100 mM). Reduction of extracellular pH from 7.4 to 6.9 was associated with a decrease in intracellular pH from 7.23 ± 0.01 to 7.01 ± 0.03. Propionate (20 mM) caused a reduction of intracellular pH to 6.97 ± 0.02, but failed to suppress store depletion-activated Ca2+entry at 2.5 mM extracellular Ca2+significantly. Our results suggest that an increase in extracellular proton concentration inhibits store depletion-activated Ca2+entry through a direct, membrane potential-independent effect on the plasmalemmal Ca2+channel.