Kageyama K
Department of Cardiovascular Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
Hokkaido Igaku Zasshi. 1995 May;70(3):497-506.
G proteins serve as transducers between cell surface receptors and intracellular effectors. They consist of three subunits, termed alpha, beta, and gamma. Recently, it has been recognized that the beta gamma subunits play an active role such as activation of beta-adrenergic receptor kinase (beta ARK). The desensitization and down-regulation of beta-adrenergic receptors have been observed in the heart failure. beta ARK is one of the components involved in desensitization of beta-adrenergic receptor and it is reported, recently, that G protein beta gamma subunits bind beta ARK through the pleckstrin homology domain. Therefore, we investigated the effects of beta-adrenergic receptor stimulation on steady-state level of G protein beta subunits (G beta) in the rat heart. The whole rat heart was preliminarily perfused for 10 min by Langendorff's technique at 60 mmHg of hydrostatic pressure with Krebs-Henseleit bicarbonate buffer, and then perfused for 30 min in the same buffer with or without 10 microM isoproterenol (ISO), 0.1mM epinephrine (EPI), 10 microM ISO with 0.1mM propranolol (PROP), or 10 microM ISO with 10 microM CGP20712A (CGP). Immunoblotting using isoform-specific antisera against G protein beta subunits revealed that the rat heart contains at least three G protein beta subunits, beta 1, beta 2 and beta 3 at molecular weight of between 35,000 and 37,000. The level of G beta 3 in the cytosol dramatically decreased in the presence of ISO alone or ISO with CGP. G beta 3 decreased in the presence of EPI as well. Propranolol could block ISO-induced decrease of G beta 3 in the cytosol. In contrast, the levels of G beta 1 and G beta 2 didn't change in the presence of ISO or EPI. On the other hand, in membrane fractions the level of G beta 3 significantly increased in the presence of ISO or EPI. ISO with PROP or ISO with CGP did not change the level of G beta 3 in membrane fractions. The levels of G beta 1 and G beta 2 did not change in the presence of ISO or EPI in membrane fractions. Taken together, beta-adrenoceptor agonist might induce isoform-specific translocation of G beta 3 from the cytosol to the membrane.
G蛋白作为细胞表面受体与细胞内效应器之间的转导分子。它们由α、β和γ三个亚基组成。最近，人们认识到βγ亚基发挥着积极作用，如激活β肾上腺素能受体激酶（βARK）。在心力衰竭中已观察到β肾上腺素能受体的脱敏和下调。βARK是参与β肾上腺素能受体脱敏的成分之一，最近有报道称，G蛋白βγ亚基通过普列克底物蛋白同源结构域与βARK结合。因此，我们研究了β肾上腺素能受体刺激对大鼠心脏中G蛋白β亚基（Gβ）稳态水平的影响。采用Langendorff技术，在60 mmHg静水压下，用Krebs-Henseleit碳酸氢盐缓冲液对大鼠全心脏进行10分钟的初步灌注，然后在相同缓冲液中，分别加入或不加入10 μM异丙肾上腺素（ISO）、0.1 mM肾上腺素（EPI）、10 μM ISO与0.1 mM普萘洛尔（PROP）或10 μM ISO与10 μM CGP20712A（CGP），再灌注30分钟。使用针对G蛋白β亚基的亚型特异性抗血清进行免疫印迹分析，结果显示大鼠心脏中至少含有三种G蛋白β亚基，即β1、β2和β3，分子量在35000至37000之间。单独使用ISO或ISO与CGP共同作用时，胞质溶胶中Gβ3的水平显著降低。EPI存在时，Gβ3也降低。普萘洛尔可阻断ISO诱导的胞质溶胶中Gβ3的降低。相反，在ISO或EPI存在时，Gβ1和Gβ2的水平没有变化。另一方面，在膜组分中，ISO或EPI存在时，Gβ3的水平显著升高。ISO与PROP或ISO与CGP共同作用时，膜组分中Gβ3的水平没有变化。在膜组分中，ISO或EPI存在时，Gβ1和Gβ2的水平没有变化。综上所述，β肾上腺素能受体激动剂可能诱导Gβ3从胞质溶胶到膜的亚型特异性易位。
