Different types of contractions in rat colon and their modulation by oxidative stress

The aim of this study was to investigate the modulation of in vitro rat colonic circular muscle contractions by dextran sodium sulfate (DSS)-induced inflammation and in spontaneous inflammation in HLA-B27 rats. We also examined the potential role of hydrogen peroxide (H₂O₂) in modulating excitation-contraction coupling. The muscle strips from the middle colon generated spontaneous phasic contractions and giant contractions (GCs), the proximal colon strips generated primarily phasic contractions, and the distal colon strips were mostly quiescent. The spontaneous phasic contractions and GCs were not affected by inflammation, but the response to ACh was suppressed in DSS-treated rats and in HLA-B27 rats. H₂O₂ production was increased in the muscularis of the inflamed colon. Incubation of colonic muscle strips with H₂O₂ suppressed the spontaneous phasic contractions and concentration and time dependently reduced the response to ACh; in the middle colon, it also increased the frequency of GCs. We conclude that H₂O₂ mimics the suppression of the contractile response to ACh in inflammation. H₂O₂ also selectively suppresses phasic contractions and increases the frequency of GCs, as found previously in inflamed dog and human colons.