Influence of Skf‐525a Congeners, Strophanthidin and Tissue‐culture Media on Desensitization in Frog Skeletal Muscle

1 Microelectrodes have been used to follow changes in membrane potential at end-plate regions of frog skeletal muscle fibres exposed to carbachol; the depolarizing drug was applied to narrow strips of muscle in a rapidly flowing solution containing relatively impermeant anions rather than chloride.2 During prolonged applications of carbachol (10 to 20 muM), the depolarization caused by the drug showed a gradual decline which was attributed to desensitization.3 Desensitization was little if at all affected by supplementing the external solution with factors present in tissue-culture media, or by treating the muscle with strophanthidin (25 muM).4 The rate of repolarization in the presence of carbachol (10 to 20 muM) was greatly increased by the SKF-525A congeners pipenzolate bromide (10 muM) and adiphenine hydrochloride (1 muM). The desensitization-enhancing action of these compounds is discussed.