Gong Haibin, Sun Hong, Koch Walter J, Rau Thomas, Eschenhagen Thomas, Ravens Ursula, Heubach Jürgen F, Adamson Dawn L, Harding Sian E
National Heart and Lung Institute, Imperial College School of Medicine, London, UK.
Circulation. 2002 May 28;105(21):2497-503. doi: 10.1161/01.cir.0000017187.61348.95.
We have observed direct (noncatecholamine-blocking) negative inotropic effects of the selective beta(2)-adrenoceptor (AR) antagonist ICI 118,551 in myocytes from failing human ventricle. In this study we characterize the effect in parallel in human myocytes and in myocytes from animal models where beta(2)ARs or G(i) proteins are overexpressed.
Enzymatically isolated, superfused ventricular myocytes were exposed to betaAR agonists and antagonists/inverse agonists, and contraction amplitude was measured. ICI 118,551 decreased contraction in ventricular myocytes from failing human hearts by 45.3+/-4.1% (n=20 hearts/31 myocytes, P<0.001) but had little effect in nonfailing hearts (4.9+/-4%, n=5 myocytes/3 hearts). Effects were significantly larger in patients classified as end-stage. Transgenic mice with high beta(2)AR number and increased G(i) levels had normal basal contractility but showed a similar negative inotropic response to ICI 118,551. Overexpression of human beta(2)AR in rabbit myocytes using adenovirus potentiated the negative inotropic effect of ICI 118,551. In human, rabbit, and mouse myocytes, the negative inotropic effects were blocked after treatment of cells with pertussis toxin to inactivate G(i), and overexpression of G(i)alpha(2) induced the effect de novo in normal rat myocytes.
We hypothesize that ICI 118,551 binding directs the beta(2)AR to a G(i)-coupled form and away from the G(s)-coupled form (ligand-directed trafficking). ICI 118,551 effectively acts as an agonist at the G(i)-coupled beta(2)AR, producing a direct negative inotropic effect. Conditions where beta(2)ARs are present and G(i) is raised (failing human heart, TGbeta(2) mouse heart) predispose to the appearance of the negative inotropic effect.
我们已经观察到选择性β₂肾上腺素能受体（AR）拮抗剂ICI 118,551对衰竭的人心室肌细胞有直接（非儿茶酚胺阻断）负性肌力作用。在本研究中，我们同时在人肌细胞以及β₂AR或G(i)蛋白过表达的动物模型的肌细胞中对该作用进行了表征。
将酶解分离、灌流的心室肌细胞暴露于βAR激动剂和拮抗剂/反向激动剂中，并测量收缩幅度。ICI 118,551使衰竭人心脏的心室肌细胞收缩降低45.3±4.1%（n = 20个心脏/31个肌细胞，P < 0.001），但对非衰竭心脏影响很小（4.9±4%，n = 5个肌细胞/3个心脏）。在被归类为终末期的患者中，该作用明显更大。β₂AR数量高且G(i)水平升高的转基因小鼠具有正常的基础收缩力，但对ICI 118,551表现出类似的负性肌力反应。使用腺病毒在兔肌细胞中过表达人β₂AR增强了ICI 118,551的负性肌力作用。在人、兔和小鼠肌细胞中，用百日咳毒素处理细胞使G(i)失活后，负性肌力作用被阻断，并且G(i)α₂的过表达在正常大鼠肌细胞中重新诱导了该作用。
我们假设ICI 118,551的结合将β₂AR导向G(i)偶联形式并使其远离G(s)偶联形式（配体导向的转运）。ICI 118,551在G(i)偶联的β₂AR上有效地充当激动剂，产生直接的负性肌力作用。存在β₂AR且G(i)升高的情况（衰竭的人心脏、TGβ₂小鼠心脏）易出现负性肌力作用。
