Schnabel P, Nohr T, Nickenig G, Paul M, Böhm M
Klinik III für Innere Medizin der Universität zu Köln, Germany.
Hypertension. 1997 Dec;30(6):1356-61. doi: 10.1161/01.hyp.30.6.1356.
The alpha1-adrenoceptor-G protein-phosphoinositide-specific phospholipase C (PLC) signal transduction pathway is assumed to play an important role in the regulation of contractile force and in the pathophysiology of myocardial hypertrophy. In the present study, the components of this pathway were investigated in left ventricles of hearts from hypertensive transgenic rats overexpressing the mouse renin gene [TG(mREN2)27] in comparison to age- and weight-matched Sprague-Dawley control rats. Contractile force was assessed in isolated electrically driven left ventricular papillary muscle strips. Alpha1-adrenoceptor density was measured by radioligand binding using [3H]prazosin, steady state levels of alpha q/11, and G protein beta-subunits by Western blotting. PLC activity was determined by a cell-free assay using exogenous phospholipid vesicles containing [3H]phosphatidylinositol (4,5)-bisphosphate as a substrate. Alpha1-adrenoceptor density was significantly increased (by 80%) in transgenic rats compared with control rats, while the positive inotropic response to the alpha1-adrenoceptor agonist phenylephrine was significantly reduced, suggesting a postreceptor defect in TG(mREN2)27. The expression of alpha q and alpha11 was verified by reverse transcription-polymerase chain reaction, and alpha q/11 steady state protein levels were shown to be similar in transgenic and control rats. Western blotting using a beta-common antibody revealed two bands at approximately 35 and 36 kD. The quantities of both were similar in TG(mREN2)27 compared with those in control rats. In contrast, PLC activity was significantly reduced (by 32%) in transgenic rats. In conclusion, our findings are consistent with a desensitization of the alpha1-adrenergic signal transduction pathway at the level of the effector.
α1 - 肾上腺素能受体 - G蛋白 - 磷脂酰肌醇特异性磷脂酶C（PLC）信号转导途径被认为在收缩力调节及心肌肥大的病理生理学过程中发挥重要作用。在本研究中，与年龄和体重匹配的Sprague - Dawley对照大鼠相比，对过表达小鼠肾素基因的高血压转基因大鼠[TG(mREN2)27]心脏的左心室中该途径的组成成分进行了研究。在分离的电驱动左心室乳头肌条中评估收缩力。使用[3H]哌唑嗪通过放射性配体结合测定α1 - 肾上腺素能受体密度，通过蛋白质印迹法测定αq/11和G蛋白β亚基的稳态水平。使用含有[3H]磷脂酰肌醇（4,5） - 二磷酸作为底物的外源性磷脂囊泡通过无细胞测定法测定PLC活性。与对照大鼠相比，转基因大鼠的α1 - 肾上腺素能受体密度显著增加（增加80%），而对α1 - 肾上腺素能受体激动剂去氧肾上腺素的正性肌力反应显著降低，提示TG(mREN2)27存在受体后缺陷。通过逆转录 - 聚合酶链反应验证了αq和α11的表达，并且显示转基因大鼠和对照大鼠的αq/11稳态蛋白水平相似。使用β通用抗体进行的蛋白质印迹显示在约35和36 kD处有两条带。与对照大鼠相比，TG(mREN2)27中两者的量相似。相反，转基因大鼠的PLC活性显著降低（降低32%）。总之，我们的研究结果与效应器水平上α1 - 肾上腺素能信号转导途径的脱敏一致。
