DIFFERENT MECHANISMS CAN ACTIVATE CA2+ ENTRANCE VIA CATION CURRENTS IN ENDOTHELIAL-CELLS

Effects of Endothelin-1 (ET-1) and cyclopiazonic acid (CPA) on non-specific cation channels in cultured bovine pulmonary artery endothelial cells (BPAECs) were investigated using the patch-clamp technique. In a bath solution containing Ca2+ as a permeant cation, 10 nM ET-1 increased inward and outward currents and this current reversed at -10 mV instead of -60 mV. Under similar conditions, 10 mu M CPA an inhibitor of Ca2+ pumps in the sarcoplasmic reticulum, also increased both currents which now reversed near -10 mV. An inorganic Ca2+ influx blocker, La3+ at 50 mu M completely blocked ET-1 and CPA-evoked currents restoring the reversal potential to -60 mV. ET-1 and CPA evoked currents were partially blocked by 50 mu M SK&F 96365 (a putative inhibitor of receptor-mediated Ca2+ entry). ET-1 and CPA increased Ca2+ influx by activation of the Ca2+-permeable non-specific cation channels, which are gated by the depletion of intracellular Ca2+ stores in endothelial cells. These results, together with a previous study demonstrating that this Ca2+ entrance pathway can be opened directly by one vasodilator (LP-805) reveal that different mechanisms exist to activate Ca2+ entrance into endothelial cells. Al may allow sustained release of endothelium-derived relaxing factor (EDRF).