Subsensitivity of adenylate cyclase and decreased beta-adrenergic receptor binding after chronic exposure to (minus)-isoproterenol in vitro.
In vitro incubation of frog erythrocytes with (minus)-isoproterenol, 0.1 mM, at 23 degrees for 10 to 24 hours caused a 63% decline (rho less than 0.001) in the maximum (minus)-isoproterenol-stimulated adenylate cyclase activity in the erythrocyte membranes. Affinity for (minus)-isoproterenol as judged by the concentration which half-maximally stimulated the enzyme was not markedly altered. Basal enzyme activity and stimulation by fluoride or prostaglandin E1 remained unaltered. The number of beta-adrenergic receptor binding sites, assessed by binding studies with the beta-adrenergic antagonist (minus)-[3-H] alprenolol, declined by 50% (rho less than 0.005) in the (minus)-isoproterenol-treated cells. The binding affinity of the sites was not changed. Regulation of the concentration of functionally active beta-adrenergic receptors in membranes may be one of the mechanisms by which chronic exposure to catecholamines desensitizes tissues to beta-adrenergic stimulation.
Mickey, J; Tate, R; Lefkowitz, RJ
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