MAST-CELL TRYPTASE REGULATES RAT COLONIC MYOCYTES THROUGH PROTEINASE-ACTIVATED RECEPTOR

Proteinase-activated receptor-2 (PAR-2) is a G protein-coupled recepto r that is cleaved and activated by trypsin-like enzymes. PAR-2 is high ly expressed by small intestinal enterocytes where it is activated by luminal trypsin. The location, mechanism of activation, and biological functions of PAR-2 in the colon, however, are unknown. We localized P AR-2 to the muscularis externa of the rat colon by immunofluorescence. Myocytes in primary culture also expressed PAR-2, assessed by immunof luorescence and RT-PCR. Trypsin, SLIGRL-NH2 (corresponding to the PAR- 2 tethered ligand), mast cell tryptase, and a filtrate of degranulated mast cells stimulated a prompt increase in [Ca2+](i) in myocytes. The response to tryptase and the mast cell filtrate was inhibited by the tryptase inhibitor BABIM, and abolished by desensitization of PAR-2 wi th trypsin. PAR-2 activation inhibited the amplitude of rhythmic contr actions of strips of rat colon. This response was unaffected by indome thacin, L-N-G-nitroarginine methyl ester, a bradykinin B-2 receptor an tagonist and tetrodotoxin. Thus, PAR-2 is highly expressed by colonic myocytes where it may be cleaved and activated by mast cell tryptase. This may contribute to motility disturbances of the colon during condi tions associated with mast cell degranulation.