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

Abstract  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‐α, IL‐1β 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.