Chloride- and voltage-dependent Ca2+ transient in cultured human aortic endothelial cells

The Cl(-)-sensitive nature of histamine-induced Ca2+ entry was investigated in cultured human aortic endothelial cells by the patch-clamp method, combined with the fluorescence measurement of intracellular Ca2+ concentration ([Ca2+]i). The sustained increase in [Ca2+]i, caused by histamine, was decreased by lowering the external concentration of Cl-. The patch-clamp experiment revealed that [Ca2+]i was dependent on the membrane potential in the presence of histamine, but not in the absence of histamine. The sustained increase in [Ca2+]i was accompanied by activation of the Cl- current, of which the reversal potential was measured to be around -28 mV with physiological internal and external Cl- concentrations. The membrane potential of the endothelial cells varied from -90 to 0 mV in the resting condition and approached the equilibrium potential for Cl- during histamine application. The results indicate that the histamine-induced Cl- current plays a functional role in the sustained increase of intracellular Ca2+ during histamine application by providing a constant driving force for Ca2+ entry across the plasma membrane.