Schwinn D A, Page S O, Middleton J P, Lorenz W, Liggett S B, Yamamoto K, Lapetina E G, Caron M G, Lefkowitz R J, Cotecchia S
Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina 27710.
Mol Pharmacol. 1991 Nov;40(5):619-26.
We recently reported the cloning of a novel alpha 1-adrenergic receptor (AR), the alpha 1CAR. By transient and stable expression of the alpha 1CAR and the previously cloned alpha 1BAR in COS-7 and HeLa cells, respectively, we have now compared their ability to interact with major signal-transduction pathways (including polyphosphoinositide hydrolysis, intracellular calcium, and cAMP metabolism), as well as their mammalian tissue localization. Both alpha 1C- and alpha 1BARs primarily couple to phospholipase C via a pertussis toxin-insensitive GTP-binding protein, leading to the release of calcium from intracellular stores. Even though alpha 1C- and alpha 1BARs activate polyphosphoinositide hydrolysis by similar biochemical mechanisms, the alpha 1CAR couples to phospholipase C more efficiently than does the alpha 1BAR; activation of the alpha 1CAR results in a 2-3-fold greater increase in inositol phosphates, compared with the alpha 1BAR. Both alpha 1AR subtypes can also increase intracellular cAMP, by a mechanism that does not involve direct activation of adenylyl cyclase. In agreement with ligand binding data, the agonist methoxamine and the antagonist WB4101 are 10-fold more potent in activating or inhibiting, respectively, the ability of the alpha 1CAR to stimulate phospholipase C, compared with the alpha 1BAR. In addition, methoxamine is almost a full agonist at the alpha 1CAR, whereas it can only weakly activate the alpha 1BAR. Tissue localization, using Northern blot analysis of total and poly(A)+-selected RNA from rabbit tissues, revealed striking mammalian species heterogeneity. As previously described, the alpha 1BAR is present in several rat tissues, including heart, liver, brain, kidney, lung, and spleen, whereas the alpha 1CAR is not present in any rat tissue studied. The alpha 1BAR is also present in rabbit aorta, heart, spleen, and kidney (and absent in rabbit liver), whereas the alpha 1CAR is present in rabbit liver. Our results indicate that the cloning and expression of different alpha 1AR subtypes represents a valuable tool to elucidate functional correlates of alpha 1AR heterogeneity.
我们最近报道了一种新型α1 - 肾上腺素能受体（AR）——α1CAR的克隆。通过分别在COS - 7细胞和HeLa细胞中瞬时和稳定表达α1CAR以及先前克隆的α1BAR，我们现在比较了它们与主要信号转导途径（包括多磷酸肌醇水解、细胞内钙和cAMP代谢）相互作用的能力，以及它们在哺乳动物组织中的定位。α1C - 和α1BARs主要通过百日咳毒素不敏感的GTP结合蛋白与磷脂酶C偶联，导致细胞内储存的钙释放。尽管α1C - 和α1BARs通过相似的生化机制激活多磷酸肌醇水解，但α1CAR与磷脂酶C的偶联比α1BAR更有效；与α1BAR相比，α1CAR的激活导致肌醇磷酸增加2 - 3倍。两种α1AR亚型也可通过不涉及腺苷酸环化酶直接激活的机制增加细胞内cAMP。与配体结合数据一致，激动剂甲氧明和拮抗剂WB4101在激活或抑制α1CAR刺激磷脂酶C的能力方面，分别比α1BAR强10倍。此外，甲氧明在α1CAR上几乎是完全激动剂，而它只能微弱地激活α1BAR。使用来自兔组织的总RNA和聚（A）+选择的RNA进行Northern印迹分析的组织定位显示出明显的哺乳动物物种异质性。如先前所述，α1BAR存在于几种大鼠组织中，包括心脏、肝脏、大脑、肾脏、肺和脾脏，而在所研究的任何大鼠组织中均不存在α1CAR。α1BAR也存在于兔主动脉、心脏、脾脏和肾脏中（兔肝脏中不存在），而α1CAR存在于兔肝脏中。我们的结果表明，不同α1AR亚型的克隆和表达是阐明α1AR异质性功能相关性的有价值工具。
