Kimura H, Miyamoto A, Ohshika H
Department of Pharmacology, School of Medicine, Sapporo Medical University, Japan.
Life Sci. 1993;53(10):PL171-6. doi: 10.1016/0024-3205(93)90511-z.
We investigated the influence of chronic beta-adrenergic stimulation on the beta-adrenoceptor-G protein-adenylyl cyclase system in rat ventricular myocardium. The rats received twice-daily injections of 4 mg/kg isoproterenol (ISO) alone or with 8 mg/kg propranolol (PROP) for 4 days. The ISO (10 microM)-induced increase in tissue cAMP production was lower (50%) after chronic ISO treatment than in control myocardium. The beta-adrenoceptor density decreased by 43% in ventricular membranes from ISO-treated rats. Immunoblotting techniques using specific antibodies against G proteins revealed that ventricular myocardium contains three Gs alpha subunit isoforms of 45, 47 and 52kDa. ISO treatment decreased levels of the three Gs alpha subunits by a total of 40%, while no change in Gi alpha (40/41kDa) and Gcommon beta (35/36kDa) levels were found in the same membrane preparations. The antagonist PROP almost totally blocked the effects of ISO treatment on cAMP, beta-adrenoceptors and Gs alpha subunits. These results suggest that chronic beta-adrenergic stimulation causes not only down-regulation of beta-adrenoceptors, but also loss of Gs alpha subunit levels in rat ventricular myocardium.
我们研究了慢性β-肾上腺素能刺激对大鼠心室心肌中β-肾上腺素能受体-G蛋白-腺苷酸环化酶系统的影响。大鼠每天接受两次注射，单独注射4mg/kg异丙肾上腺素（ISO）或与8mg/kg普萘洛尔（PROP）联合注射，持续4天。慢性ISO治疗后，ISO（10μM）诱导的组织cAMP生成增加量低于对照心肌（降低了50%）。ISO处理大鼠心室膜中的β-肾上腺素能受体密度降低了43%。使用针对G蛋白的特异性抗体的免疫印迹技术显示，心室心肌含有三种分子量分别为45、47和52kDa的Gsα亚基同工型。ISO处理使三种Gsα亚基的水平总共降低了40%，而在相同的膜制剂中未发现Giα（40/41kDa）和G共同β（35/36kDa）水平有变化。拮抗剂PROP几乎完全阻断了ISO处理对cAMP、β-肾上腺素能受体和Gsα亚基的影响。这些结果表明，慢性β-肾上腺素能刺激不仅导致大鼠心室心肌中β-肾上腺素能受体下调，还导致Gsα亚基水平降低。
