Background and Aims: The characteristics of colonic circular smooth muscle slow waves are altered during inflammation. The aim of this study was to examine whether inflammation modulates the open-state probability of Ca2+-activated K+ (K(Ca)) channels in these cells to contribute to these alterations. Methods: The experiments were performed on freshly dissociated single smooth muscle cells from the canine colon using standard patch clamp methods. Inflammation was induced by mucosal exposure to ethanol and acetic acid. Results: Inflammation decreased the open-state probability of large- conductance K(Ca) (BK) channels in the cell-attached and excised inside-out configurations. The voltage sensitivity of the channels was also reduced during inflammation. Inflammation had no significant effect on the large, medium, and small conductances or the unitary current levels of channel openings. However, it decreased the maximum number of simultaneous channel openings. The channels were Ca2+-dependent and were blocked by tetraethylammonium and charybdotoxin in normal and inflamed cells. Conclusions: Inflammation decreases the open-state probability of BK channels. This may partially reverse the decrease in duration and amplitude of slow waves and depolarization of membrane potential seen in inflammation.
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