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 tiss ue distribution and is involved in many physiological functions. Because th rombin 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 sho rt-circuit current. The secretory effect was blocked by BaCl2 and the Ca2+- ATPase inhibitor thapsigargin, but not by the L-type Ca2+ channel blocker v erapamil or DIDS, the nonselective inhibitor of Ca2+-dependent Cl- transpor t. Responses to thrombin and PAR-1-activating peptides exhibited auto- and crossdesensitization. Fura 2-loaded SCBN cells had increased fluorescence a fter PAR-1 activation, indicating increased intracellular Ca2+. RT-PCR show ed that SCBN cells expressed mRNA for the cystic fibrosis transmembrane con ductance regulator (CFTR) and hypotonicity-activated Cl- channel-2 but not for the Ca2+ dependent Cl- channel-1. PAR-1 activation failed to increase i ntracellular cAMP, suggesting that the CFTR channel is not involved in the Cl- secretory response. Our data demonstrate that PAR-1 is expressed on hum an intestinal epithelial cells and regulates a novel Ca2+-dependent Cl- sec retory pathway. This may be of clinical significance in inflammatory intest inal diseases with elevated thrombin levels.