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ß‐Adrenergic Receptor Activation Increases Acetylcholine Receptor Number in Cultured Skeletal Muscle Myotubes

Treatment of embryonic chick muscle myotubes with the ß‐adrenergic agonist isoproterenol increased the number of surface membrane nicotinic cholinergic receptors. Receptor degradation was unaffected by isoproterenol, suggesting that receptor synthesis was increased. The effect of isoproterenol appears to be mediated by the ß‐adrenergic receptor adenylate cy‐clase system for the following reasons: (a) The response to isoproterenol was dose‐dependent and stereospecific. (b) The response to catecholamines followed the order isoproterenol > epinephrine > norepinephrine. (c) Al‐prenolol, a ß‐adrenergic antagonist, but not phen‐tolamine, an a‐antagonist, abolished the effect, (d) The maximal effects of isoproterenol and cholera toxin, an activator of adenylate cyclase, were not additive. These results suggest that under certain physiological states catecholamines may play an important role in the regulation of cholinergic receptors.