Effects of cromakalim on the contraction and the membrane potential of the circular smooth muscle of guinea‐pig stomach

Abstract

. The effects of cromakalim on mechanical and electrical activities of the circular smooth muscles of guinea‐pig stomach antrum were observed. . Cromakalim (> 1 × 10−7 m) decreased the amplitude of spontaneous rhythmic contractions and also the acetylcholine‐enhanced spontaneous contractions. Cromakalim was less effective against the 25.9 mm and 35.9 mm K+‐induced tonic contractions. . Glibenclamide (1 × 10−6 m) itself caused no detectable change in the spontaneous contractions, those potentiated by acetylcholine or tonic contractions induced by high K+ solutions, but attenuated the actions of cromakalim. On the other hand, charybdotoxin (3 × 10−8 m) increased the amplitude of spontaneous contractions but failed to affect the actions of cromakalim. . Cromakalim (> 1 × 10−6 m) decreased the amplitude and duration of slow waves, and hyperpolarized the membrane. These actions of cromakalim were completely antagonized by 1 × 10−6 m glibenclamide, whereas part of the effects of cromakalim on mechanical activity was resistant to glibenclamide. . The results suggest that the inhibition by cromakalim of the electrical activity and the hyperpolarization, which may be associated with the opening of glibenclamide‐sensitive K+ channel, are responsible for its inhibitory action on circular smooth muscle of guinea‐pig stomach. Further, some effects independent of glibenclamide‐sensitive K+ channel may also be responsible for the mechanical effect. 1992 British Pharmacological Society