title: (+/-)-[3H]Epinephrine and (-)[3H]dihydroalprenolol binding to beta1- and beta2-noradrenergic receptors in brain, heart, and lung membranes.
abstract: (+/-)-[3H]Epinephrine binds to beta-receptors in calf cerebellar and rat lung membranes in the presence of 1.0 mM pyrocatechol and 1.0 microM phentolamine, with dissociation constants at 4 degrees C of 11 nM and 24 nM, respectively. (+/-)-[3H]Epinephrine associates to equilibrium within 20 min in both tissues, and over 50% of the binding is rapidly dissociable. Inhibition of binding by agonists and antagonists is highly stereoselective, and the structure-activity relationships of adrenergic agents in inhibiting (+/-)-[3H]epinephrine binding suggest an interaction with beta2 type noradrenergic receptors. (-)-Isoproterenol has an apparent Ki of 2 nM, (-)-epinephrine is 1.5 to 3 times weaker, and (-)-norepinephrine is 30 to 60 times weaker. Salbutamol and terbutaline, selective beta2-agonists, are potent inhibitors of binding, as are several nonspecific antagonists. Properties of the sites labeled by (+/-)-[3H]epinephrine in calf cerebellum and rat lung are closely similar. (-)-[3H]Dihydroalprenolol binding in calf cerebellum and rat lung also shows beta2 characteristics. Antagonists have similar potencies in inhibiting (-)-[3H]dihydroalprenolol and (+/-)-[3H]epinephrine binding in both tissues, but agonists are in general more potent inhibitors of (+/-)-[3H]epinephrine. Sodium and lithium selectively lower the affinity of (+/-)-[3H]epinephrine at its binding sites and the affinities of agonists, but not antagonists, at the (-)-[3H]dihydroalprenolol site. Specific (+/-)-[3H]epinephrine binding was not detectable in calf cortex and rat heart, where (-)-[3H]dihydroalprenolol binding suggests a beta1-receptor. A physiological significance of (+/-)-[3H]epinephrine binding is suggested by the strong correlation for agonists and antagonists between affinities in inhibiting binding, and in stimulating or inhibiting a beta-receptor-coupled adenylate cyclase in frog erythrocytes.
mesh_terms: D000526:Alprenolol / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism*; D007700:Kinetics; D008168:Lung / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D000526:Alprenolol; D004837:Epinephrine