ATP-induced chloride current and tonic increase of internal Ca2+ concentration in vascular endothelial cells.

The effect of ATP on membrane currents and the intracellular Ca2+ concentration was investigated in cultured human aortic endothelial cells. ATP (10 microM) activated the Cl- current within a few minutes following a rapid activation of the K+ current. Fura-2 fluorometry showed that ATP increased [Ca2+]i with a biphasic time course. The tonic phase was markedly depressed by both an increase in [K+]o to 140 mM and a decrease in [Cl-]o to 20 mM. ATP activated not only Ca(2+)-activated K+ channels but also Cl- channels to regulate the membrane potential related to the tonic phase of the [Ca2+]i increase.