Brechler V, Levens N R, De Gasparo M, Bottari S P
Cardiovascular Department, Ciba-Geigy Ltd., Basel, Switzerland.
Recept Channels. 1994;2(2):79-87.
Ever since the identification of two distinct Ang II receptor subtypes, the function of the AT2 receptor has been a subject of debate. As opposed to the AT1 subtype, this receptor does not interact with G-proteins in most cell lines and tissues. We show here that, in intact PC12W cells which express only AT2 receptors, Ang II significantly decreases basal and atrial natriuretic peptide (ANP)-stimulated cGMP concentration. This effect is mimicked by the AT2 selective agonist CGP 42112, and is not prevented by the AT1 selective antagonist losartan, indicating that this is an AT2 receptor mediated response. The lack of effect of the phosphodiesterase (PDE) inhibitor IBMX shows that this mechanism does not involve PDE stimulation. This is confirmed by the finding that neither Ang II or CGP 42112 affect the Ca++/calmodulin dependent cGMP PDE activity. Furthermore Ang II and CGP 42112 have no effect on nitroprusside-stimulated cGMP levels in these cells, thus ruling out interactions between the AT2 receptor and soluble guanylate cyclase. These data indicate that the AT2 receptor mediated decrease of cGMP is due to the selective inhibition of particulate guanylate cyclase (pGC) activity. In an accompanying paper we report that interaction of Ang II with the AT2 receptor in the same cells results in the stimulation of phosphotyrosine phosphatase (PTPase) activity. Interestingly, the PTPase inhibitors sodium orthovanadate and phenylarsine oxyde, but not the Ser/Thr phosphatase inhibitor okadiac acid, inhibitthe Ang II and CGP 42112 induced decreases in cellular cGMP concentration. These findings suggest that stimulation of PTPase activity may be involved in the regulation of pGC activity via AT2 receptors.
自从两种不同的血管紧张素II（Ang II）受体亚型被鉴定出来后，AT2受体的功能一直是一个争论的话题。与AT1亚型不同，该受体在大多数细胞系和组织中不与G蛋白相互作用。我们在此表明，在仅表达AT2受体的完整PC12W细胞中，Ang II显著降低基础和心房利钠肽（ANP）刺激的环鸟苷酸（cGMP）浓度。AT2选择性激动剂CGP 42112可模拟这种效应，且AT1选择性拮抗剂氯沙坦不能阻止这种效应，表明这是一种由AT2受体介导的反应。磷酸二酯酶（PDE）抑制剂异丁基甲基黄嘌呤（IBMX）无效，表明该机制不涉及PDE刺激。这一点通过以下发现得到证实：Ang II或CGP 42112均不影响钙/钙调蛋白依赖性cGMP PDE活性。此外，Ang II和CGP 42112对这些细胞中硝普钠刺激的cGMP水平没有影响，从而排除了AT2受体与可溶性鸟苷酸环化酶之间的相互作用。这些数据表明，AT2受体介导的cGMP降低是由于颗粒性鸟苷酸环化酶（pGC）活性的选择性抑制。在一篇配套论文中我们报告，Ang II与同一细胞中的AT2受体相互作用会导致磷酸酪氨酸磷酸酶（PTPase）活性的刺激。有趣的是，PTPase抑制剂原钒酸钠和氧化苯胂，但丝氨酸/苏氨酸磷酸酶抑制剂冈田酸则不能抑制Ang II和CGP 42112诱导的细胞cGMP浓度降低。这些发现表明，PTPase活性的刺激可能通过AT2受体参与pGC活性的调节。
