Marzo K P, Frey M J, Wilson J R, Liang B T, Manning D R, Lanoce V, Molinoff P B
Cardiovascular Section, Hospital of the University of Pennsylvania, Philadelphia 19104-4283.
Circ Res. 1991 Dec;69(6):1546-56. doi: 10.1161/01.res.69.6.1546.
Changes in the beta-adrenergic receptor-G protein-adenylate cyclase complex were investigated in an experimental canine model of low-output heart failure produced by chronic rapid ventricular pacing. The contractile response occurring after exposure to the beta-adrenergic agonist dobutamine, measured as peak left ventricular + dP/dt, was decreased after 3 weeks of pacing. To further characterize the diminished functional responsiveness to beta-adrenergic receptor stimulation, beta-adrenergic receptor-adenylate cyclase coupling was investigated using membranes prepared from both control and paced animals. The density of beta-adrenergic receptors was decreased by 40% with a selective downregulation of the beta 1-subtype. The affinity of the receptor for the antagonist radioligand [125I]iodocyanopindolol remained unchanged. A defect in coupling was suggested by a decreased ability of isoproterenol, fluoride, and forskolin to stimulate adenylate cyclase in membranes prepared from failing hearts. Determination of the levels of Gi alpha (the alpha-subunit of Gi) by immunoblotting and pertussis toxin labeling revealed modest increases of approximately 30%. Furthermore, Mn2+ and purified Gs failed to stimulate adenylate cyclase in membranes prepared from failing hearts, indicating an impairment in the catalytic moiety of adenylate cyclase itself or in the ability of adenylate cyclase to couple to Gs. In contrast, complementation assay did not reveal differences in the functional activity of Gs alpha (the alpha-subunit of Gs). Taken together, these data demonstrate a selective decrease in the beta 1-subtype of adrenergic receptors and an increase in a 40-kd G1-like protein in the failing heart. Similar changes have been described in human idiopathic dilated cardiomyopathy. In addition to these changes, we identified a possible defect at the level of the catalytic subunit of adenylate cyclase.
在通过慢性快速心室起搏建立的低输出量心力衰竭实验犬模型中，研究了β-肾上腺素能受体-G蛋白-腺苷酸环化酶复合物的变化。以左心室压力上升最大速率（+dP/dt）峰值衡量，暴露于β-肾上腺素能激动剂多巴酚丁胺后出现的收缩反应，在起搏3周后降低。为进一步明确对β-肾上腺素能受体刺激的功能反应性降低的特征，使用从对照动物和起搏动物制备的膜片研究了β-肾上腺素能受体-腺苷酸环化酶偶联。β-肾上腺素能受体密度降低了40%，β1亚型选择性下调。受体与拮抗剂放射性配体[125I]碘氰吲哚洛尔的亲和力保持不变。异丙肾上腺素、氟化物和福斯可林刺激衰竭心脏制备的膜片中腺苷酸环化酶的能力下降，提示存在偶联缺陷。通过免疫印迹和百日咳毒素标记测定Giα（Gi的α亚基）水平，显示有大约30%的适度升高。此外，Mn2+和纯化的Gs未能刺激衰竭心脏制备的膜片中的腺苷酸环化酶，表明腺苷酸环化酶本身的催化部分或腺苷酸环化酶与Gs偶联的能力受损。相比之下，互补试验未显示Gsα（Gs的α亚基）功能活性存在差异。综上所述，这些数据表明衰竭心脏中肾上腺素能受体的β1亚型选择性减少，以及一种40-kd G1样蛋白增加。在人类特发性扩张型心肌病中也描述了类似的变化。除了这些变化，我们还在腺苷酸环化酶催化亚基水平发现了一个可能的缺陷。
