Differences in reactivity of rat and chick skeletal muscle cells in culture to prolonged exposure to cholinoceptor agonists

Depolarization induced by acetylcholine, methacholine, and oxotremorine was measured in myotubes cultured from rat and chick skeletal muscle and from rat thymus glands. Responses of chick myotubes to acetylcholine rapidly waned, indicating desensitization, but these cells were not depolarized by oxotremorine or methacholine. Depolarization of rat myotubes by acetylcholine was maintained throughout its application, but responses to oxotremorine and methacholine spontaneously diminished. Rat thymotubes had fading responses to all three agonists. With rat myotubes and thymotubes, exposure to any one agonist diminished subsequent responses to the others. Thus, the muscle cells cultured from different sources respond differently to prolonged application of cholinoceptor agonists. The unusual characteristics of rat cells in culture may be a feature of immature muscle that changes during development.