Mickey J, Tate R, Lefkowitz R J
J Biol Chem. 1975 Jul 25;250(14):5727-9.
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.
在23摄氏度下，将青蛙红细胞与0.1 mM的（-）-异丙肾上腺素进行体外孵育10至24小时，导致红细胞膜中最大（-）-异丙肾上腺素刺激的腺苷酸环化酶活性下降63%（ρ<0.001）。根据半最大刺激该酶的浓度判断，对（-）-异丙肾上腺素的亲和力没有明显改变。基础酶活性以及氟化物或前列腺素E1的刺激作用保持不变。通过与β-肾上腺素能拮抗剂（-）-[3-H]阿普洛尔进行结合研究评估，（-）-异丙肾上腺素处理的细胞中β-肾上腺素能受体结合位点的数量下降了50%（ρ<0.005）。这些位点的结合亲和力没有改变。膜中功能性活性β-肾上腺素能受体浓度的调节可能是长期暴露于儿茶酚胺使组织对β-肾上腺素能刺激脱敏的机制之一。
