INFLUENCE OF SKF‐525A CONGENERS, STROPHANTHIDIN AND TISSUE‐CULTURE MEDIA ON DESENSITIZATION IN FROG SKELETAL MUSCLE

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Abstract
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 μm), 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 μm). 4 The rate of repolarization in the presence of carbachol (10 to 20 μm) was greatly increased by the SKF-525A congeners pipenzolate bromide (10 μm) and adiphenine hydrochloride (1 μm). The desensitization-enhancing action of these compounds is discussed.