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 col onic circular muscle contractions by dextran sodium sulfate (DSS)-induced i nflammation and in spontaneous inflammation in HLA-B27 rats. We also examin ed the potential role of hydrogen peroxide (H2O2) in modulating excitation- contraction coupling. The muscle strips from the middle colon generated spo ntaneous phasic contractions and giant contractions (GCs), the proximal col on strips generated primarily phasic contractions, and the distal colon str ips were mostly quiescent. The spontaneous phasic contractions and GCs were not affected by inflammation, but the response to ACh was suppressed in DS S-treated rats and in HLA-B27 rats. H2O2 production was increased in the mu scularis of the inflamed colon. Incubation of colonic muscle strips with H2 O2 suppressed the spontaneous phasic contractions and concentration and tim e dependently reduced the response to ACh; in the middle colon, it also inc reased the frequency of GCs. We conclude that H2O2 mimics the suppression o f the contractile response to ACh in inflammation. H2O2 also selectively su ppresses phasic contractions and increases the frequency of GCs, as found p reviously in inflamed dog and human colons.