Interaction between Acetylcholine and Sterols in Tissues

Abstract

WE have recently carried out some experiments on the form of the contraction given by the gastrocnemius muscle of a winter frog¹ in response to a single electrical stimulus. In certain circumstances, of which the most important is the presence of thyroxine at slightly above the physiological concentration in the Ringer's solution in which the muscle is bathed, the muscle gives an abnormal prolonged contraction if either acetylcholine or one of several sterols is added to the medium. This abnormal contraction greatly resembles a tetanic contraction in form. It is of exactly the same type whether it is produced by the addition of acetylcholine or of a sterol. Further, if both acetylcholine and a sterol are added to the medium together, in a proportion which is different for different sterols but is well-djfined for each, the contraction remains a normal twitch and shows no tendency to become prolonged. So long as this proportion between the concentrations of acetylcholine and sterol in the medium is maintained, the concentrations of both may be altered over a wide range and the contraction will remain a normal twitch.