Proteinase-activated receptors-1 and 2 induce electrogenic Cl−secretion in the mouse cecum by distinct mechanisms

Abstract

Proteinase-activated receptors (PAR1-PAR4) belong to a family of G protein-coupled receptors that are cleaved by proteases. Previous in vitro studies on the mouse large intestine have indicated that PAR1and PAR2were involved in regulating epithelial ion transport, but that their roles were different between the proximal and distal colon. This present study was done to elucidate the roles of PAR1and PAR2in regulating anion secretion in the cecum, another segment of the large intestine. A mucosa-submucosal sheet of the mouse cecum was mounted in Ussing chambers, and the short-circuit current ( Isc) was measured. The addition of a PAR1-activating peptide (SFFLRN-NH2) to the serosal surface increased Isc. This increase in Iscinduced by SFFLRN-NH2was partially suppressed by serosal bumetanide and substantially suppressed by mucosal 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and by the removal of Cl−from the bathing solution. The Iscincrease was also substantially suppressed by serosal tetrodotoxin (TTX) and neurokinin-1 receptor antagonist L-703,606 and was partially inhibited by serosal atropine and hexamethonium. The addition of a PAR2-activating peptide (SLIGRL-NH2) to the serosal surface also induced an increase in Isc; this increase was partially suppressed by bumetanide and substantially suppressed by NPPB and by the removal of Cl−, but not by TTX. The expression of mRNA for PAR1and PAR2was confirmed in the mucosa as determined by RT-PCR. In conclusion, PAR1and PAR2both induced Cl−secretion in the mouse cecum. This secretion mediated by PAR1probably occurred by activation of the receptor on the submucosal secretomotor neurons, resulting mainly in the release of tachykinins and activation of the neurokinin-1 receptor, and partly in the release of ACh and activation of the muscarinic and nicotinic receptors. On the other hand, PAR2-mediated Cl−secretion probably occurred by activating the receptor on the epithelial cells. A variety of proteases would induce fluid secretion mediated by PAR1and PAR2in the cecum and thereby support bacterial fermentation and participate in mucosal inflammation.