Thrombin potentiates volume-activated chloride currents in pulmonary artery endothelial cells

In bovine pulmonary artery endothelial cells, ionic currents and the concentration of free intracellular Ca2+ ([Ca2+]i) were measured with a combined patch clamp and Ca(2+)-fluorimetric method (Fura-2). Volume-activated Cl-currents (ICl,vol) were activated by a 13 or 28% decrease in tonicity. Thrombin, 1 U/ml, strongly potentiated ICl,vol preactivated by low hypotonicity (13% HTS) but had no effect on ICl,vol preactivated by stronger hypotonic challenges (28% HTS). The thrombin-induced potentiation was not affected by buffering [Ca2+]i at 50-100 nmol/l and omitting extracellular Ca2+. A peptide agonist of the thrombin receptor, SFLLRN, also potentiated ICl,vol, while an enzymatically inactive thrombin analogue, DIP-thrombin, was without effect. These result suggest that proteolytic activation of the thrombin receptor sensitises the activation of ICl,vol in endothelial cells in a Ca(2+)-independent mechanism.