Different susceptibilities of spontaneous rhythmicity and myogenic contractility to intestinal muscularis inflammation in the hapten-induced colitis

We examined the time-dependent changes in the immunoreactivity of the smooth muscle region and the accompanying motility disorder in a hapten-induced rat model of colitis. Histological analysis and myeloperoxidase (MPO) activity indicated that inflammatory cells infiltrated into the muscle layer at 2 days after 2,4,6-trinitrobenzenesulphonic acid (TNBS) treatment. The infiltrated immune cells then gradually decreased in number, but were still present at 14 days. The expression of proinflammatory cytokine mRNAs (TNF-alpha, IL-1 beta and IL-6) and proteins in the muscle layer was increased at 2 days, then began to decrease, returning to control levels at 14 days. The frequency of spontaneous rhythmicity was suppressed at 2 and 7 days, and returned to control levels at 14 days. Consistent with these observations, the immunoreactivity of the interstitial cells of Cajal network was disrupted at 2 and 7 days, which then gradually reformed at 14 days. On the other hand, the myogenic contractions induced by high K+ and carbachol were decreased at 2 days, and were still inhibited at 14 days. These results suggest that spontaneous rhythmicity dysfunction may improve more rapidly than myogenic contractility dysfunction in a hapten-induced rat model of colitis.