Metabolic dependency of ionophore A23187-induced contraction of ileal longitudinal smooth muscle.

Abstract

1. Tonic contraction in response to K+ is well known to be highly dependent on aerobic metabolism in ileal muscle. The ionophore A23187 (10(-5) M) induced an initial contraction and successive rhythmic contraction in ileal muscle, but did not induce tonic contraction. This study, therefore, was performed to investigate the metabolic dependency during contraction induced by A23187. 2. Under hypoxic conditions, A23187 (10(-5) M) induced an initial contraction accompanied by an increase in lactate release. However, it induced only small rhythmic contractions and decreases in ATP, phosphocreatinine (PCr) and glycogen contents. 3. In glucose-free medium, A23187 (10(-5) M) induced an initial contraction and concomitant significant decrease in the ATP and glycogen contents. However, it did not induce successive rhythmic contractions. In 'glycogen-depleted muscle' stimulated repeatedly with 60 mM K+ in glucose-free medium, 60 mM K+ induced a phasic contraction without tonic contraction. A23187 induced no contraction under these conditions. 4. These results suggested that the initial contraction induced by A23187 was dependent on endogenous glycogen, while successive rhythmic contractions were dependent on aerobic metabolism after supply of external glucose to the ileal muscle.