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

Abstract

 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 Ca²⁺-fluorimetric method (Fura-2). Volume-activated Cl^––currents (I_Cl,vol) were activated by a 13 or 28% decrease in tonicity. Thrombin, 1 U/ml, strongly potentiated I_Cl,vol preactivated by low hypotonicity (13% HTS) but had no effect on I_Cl,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 I_Cl,vol, while an enzymatically inactive thrombin analogue, DIP-thrombin, was without effect. These results suggest that proteolytic activation of the thrombin receptor sensitises the activation of I_Cl,vol in endothelial cells in a Ca²⁺-independent mechanism.