Impairment of PAR-2-mediated relaxation system in colonic smooth muscle after intestinal inflammation

1 Protease-activated receptor (PAR)-2 plays important roles in intestinal inflammatory responses. Changes in PAR-2-mediated smooth muscle function may contribute pathophysiologically to the intestinal motility disorders often observed in inflammatory bowel disease (IBD). 2 Stimulation of PAR-2 by trypsin-induced relaxation of carbachol- and KCl-induced contractions in normal rat colonic smooth muscle was completely resolved by tissue pretreatment with apamin, but not by pretreatment with l-NMMA or a cocktail of neuronal blockers (tetrodotoxin, hexamethonium and propranolol). 3 In colon inflamed by dextran sodium sulphate (DSS), trypsin-induced inhibitory effects were significantly reduced. Relaxation induced by SLIGRL-NH2, a selective PAR-2-activating peptide, was also reduced in DSS-treated rat colon. However, inhibitory effects of 1-ethylbenzimidazolin-2-one, an activator of small conductance Ca2+-activated K+ channel, were unaffected. 4 Expression of PAR-2 mRNA in colonic muscularis externa was significantly lower in DSS-treated rats than in control rats. 5 These results suggest that the PAR-2 mediated relaxation system in colonic smooth muscle is suppressed in this experimental colitis rat model, and may contribute to motility disorders in IBD.