Borst S E, Hui K K, Conolly M E
Division of Clinical Pharmacology, UCLA School of Medicine.
Pharmacology. 1990;40(6):325-9. doi: 10.1159/000138681.
beta-Adrenergic receptors on isolated human lymphocytes were enumerated using 125I-cyanopindolol (125I-CYP), after a 90-min exposure to 50 mumols/l l-isoproterenol in vitro. No change in receptor density could be shown in assays performed at 37 degrees C, although a 40% reduction was apparent in binding studies carried out at 4 degrees C. In contrast, beta-adrenergic receptors on lymphocytes from mild asthmatics after a 3-week course of oral terbutaline showed a 40% reduction in receptor density regardless of the assay temperature, in addition to a 2.5-fold reduction in the receptor affinity for isoproterenol. The data are consistent with reports that a fraction of receptors are sequestered during short-term exposure to agonists. Sequestered receptors may or may not be detected by radioligand binding assays depending on the ligand of choice, temperature of the binding assay and duration of prior exposure to the agonist. After extended exposure to an agonist in vivo, the number of surface receptors was reduced, and sequestered receptors were not present, presumably as a result of degradation.
体外将人离体淋巴细胞暴露于50μmol/L的L-异丙肾上腺素90分钟后，用125I-氰吲哚洛尔（125I-CYP）对β-肾上腺素能受体进行计数。在37℃进行的检测中未显示受体密度有变化，尽管在4℃进行的结合研究中明显降低了40%。相比之下，轻度哮喘患者的淋巴细胞在口服特布他林3周疗程后，无论检测温度如何，受体密度均降低40%，此外，受体对异丙肾上腺素的亲和力降低了2.5倍。这些数据与以下报道一致，即一部分受体在短期暴露于激动剂期间会被隔离。根据所选择的配体、结合测定的温度以及先前暴露于激动剂的持续时间，放射性配体结合测定可能检测到也可能检测不到被隔离的受体。在体内长时间暴露于激动剂后，表面受体数量减少，并且不存在被隔离的受体，这可能是降解的结果。
