Protease-activated receptor-1 stimulates Ca2+-dependent Cl- secretion in human intestinal epithelial cells

The thrombin receptor, protease-activated receptor-1 (PAR-1), has wide tissue distribution and is involved in many physiological functions. Because thrombin is in the intestinal lumen and mucosa during inflammation, we sought to determine PAR-1 expression and function in human intestinal epithelial cells. RT-PCR showed PAR-1 mRNA expression in SCBN cells, a nontransformed duodenal epithelial cell line. Confluent SCBN monolayers mounted in Ussing chambers responded to PAR-1 activation with a Cl--dependent increase in short-circuit current. The secretory effect was blocked by BaCl2 and the Ca2+-ATPase inhibitor thapsigargin, but not by the L-type Ca2+ channel blocker verapamil or DIDS, the nonselective inhibitor of Ca2+-dependent Cl- transport. Responses to thrombin and PAR-1-activating peptides exhibited auto- and crossdesensitization. Fura 2-loaded SCBN cells had increased fluorescence after PAR-1 activation, indicating increased intracellular Ca2+. RT-PCR showed that SCBN cells expressed mRNA for the cystic fibrosis transmembrane conductance regulator (CFTR) and hypotonicity-activated Cl- channel-2 but not for the Ca2+ dependent Cl- channel-1. PAR-1 activation failed to increase intracellular cAMP, suggesting that the CFTR channel is not involved in the Cl- secretory response. Our data demonstrate that PAR-1 is expressed on human intestinal epithelial cells and regulates a novel Ca2+-dependent Cl- secretory pathway. This may be of clinical significance in inflammatory intestinal diseases with elevated thrombin levels.