Miyamoto A, Kawana S, Kimura H, Ohshika H
Department of Pharmacology, School of Medicine, Sapporo Medical University, Japan.
Eur J Pharmacol. 1994 Jan 15;266(2):147-54. doi: 10.1016/0922-4106(94)90104-x.
We have recently reported that the responsiveness of adrenoceptors is decreased with aging in rat ventricular myocardium. Thus, the current study determined aging-dependent changes in: (a) characteristics of myocardial G proteins as determined by Western blot analysis; (b) steady-state levels of G protein mRNA as determined by Northern blot analysis; and (c) the intropic response to isoproterenol, a beta-adrenoceptor agonist. Cardiac preparations were isolated from male Wistar rats of 6 (adult) and 24 (old) months old. Compared with adults, aging decreased the combined level of the three Gs alpha subunits (45, 47 and 52 kDa) by a total of 23% in ventricular membrane preparations. In contrast, levels of Gi alpha (40/41 kDa), Gq alpha (42 kDa), Go alpha (39 kDa) and G common beta (35/36 kDa) immunoreactivity were not affected by aging in the same membrane preparations. In ventricular myocardium, steady-state levels of Gs alpha mRNA (1.9 kb) decreased by 20-28% between 6 and 24 months of age with no change in Gi alpha mRNA (2.4 kb). An aging-associated decline in beta-adrenergic stimulation was observed in the maximum positive inotropic effect elicited by isoproterenol in the presence of prazosin in left papillary muscles, with no change in ED50 values. These results suggest that age-related changes in cardiac excitation and contraction coupling following beta-adrenoceptor stimulation are mediated, at least in part, by Gs alpha protein dysfunction.
我们最近报道，大鼠心室肌中肾上腺素能受体的反应性随衰老而降低。因此，本研究确定了衰老相关的变化：(a) 通过蛋白质免疫印迹分析测定的心肌G蛋白特征；(b) 通过Northern印迹分析测定的G蛋白mRNA的稳态水平；(c) 对β-肾上腺素能受体激动剂异丙肾上腺素的变力反应。从6个月（成年）和24个月（老年）的雄性Wistar大鼠中分离心脏标本。与成年大鼠相比，衰老使心室膜制剂中三种Gsα亚基（45、47和52 kDa）的总水平降低了23%。相比之下，在相同的膜制剂中，Giα（40/41 kDa）、Gqα（42 kDa）、Goα（39 kDa）和通用Gβ（35/36 kDa）的免疫反应性水平不受衰老影响。在心室肌中，6至24个月龄之间，Gsα mRNA（1.9 kb）的稳态水平下降了20-28%，而Giα mRNA（2.4 kb）没有变化。在存在哌唑嗪的情况下，左乳头肌中异丙肾上腺素引起的最大正性变力作用中观察到β-肾上腺素能刺激的衰老相关下降，ED50值没有变化。这些结果表明，β-肾上腺素能受体刺激后心脏兴奋与收缩偶联的年龄相关变化至少部分是由Gsα蛋白功能障碍介导的。
