Response of white adipocyte of mouse and rabbit to catecholamines and ACTH. 3. Modified binding properties of beta-adrenoreceptor and its decreased coupling efficiency for adenylate cyclase.

Using (-)-[3H]-dihydroalprenolol ([3H]-DHA) and [3H]-norepinephrine ([3H]-NE) as probes, adrenoreceptors in mouse and rabbit adipocyte plasma membranes were studied and compared. The binding of either radioligand can be displaced by propranolol, alprenolol, isoproterenol or norepinephrine. [3H]-Norepinephrine bound to rabbit plasma membrane can be displaced by phentolamine. Based on displacement of radioligand by unlabelled stereoisomers, the binding is stereospecific for the (-) stereoisomer. Quantitative binding determinations of catecholamine radioligand as well as competitive inhibitory and displacement studies with Scatchard plots where appropriate, allowed calculation of binding parameters including Bmax and Kd for both radioligands and for the compounds listed above. Kinetics of displacement were also followed. Based on these binding parameters and kinetics, together with the activity of hormone and NaF sensitive adenylate cyclase, we conclude that both the population of beta-adrenoreceptor and its coupling efficiency for adenylate cyclase of the rabbit plasma membrane appear to be low as compared to that of mouse and rat.