Mechanism of Contraction of Smooth Muscle by Drugs

Abstract

IT is generally believed that the process which initiates contraction in striated muscle is the depolarization of the excitable membrane of the muscle fibre, although the mechanism by which membrane excitation is linked with the contractile process is unknown¹. When smooth muscle is caused to contract by acetylcholine there is a decrease in membrane potential², and it would seem reasonable to assume that the sequence of events following action of the drug on the excitable membrane is similar to that postulated for striated muscle, namely, depolarization leading to activation of the contractile element. The following experiments in which the effects of drugs were tested on smooth muscle which had been depolarized by the external administration of potassium ions suggest, however, that activation of the contractile element can be initiated by acetylcholine and other drugs without intervening depolarization.