Perroy J, Prezeau L, De Waard M, Shigemoto R, Bockaert J, Fagni L
Centre National de la Recherche Scientifique, Unité Propre de Recherche 9023, Centre CNRS-INSERM de Pharmacologie et d'Endocrinologie, 34000 Montpellier, France.
J Neurosci. 2000 Nov 1;20(21):7896-904. doi: 10.1523/JNEUROSCI.20-21-07896.2000.
Although presynaptic localization of mGluR7 is well established, the mechanism by which the receptor may control Ca(2+) channels in neurons is still unknown. We show here that cultured cerebellar granule cells express native metabotropic glutamate receptor type 7 (mGluR7) in neuritic processes, whereas transfected mGluR7 was also expressed in cell bodies. This allowed us to study the effect of the transfected receptor on somatic Ca(2+) channels. In transfected neurons, mGuR7 selectively inhibited P/Q-type Ca(2+) channels. The effect was mimicked by GTPgammaS and blocked by pertussis toxin (PTX) or a selective antibody raised against the G-protein alphao subunit, indicating the involvement of a G(o)-like protein. The mGuR7 effect did not display the characteristics of a direct interaction between G-protein betagamma subunits and the alpha1A Ca(2+) channel subunit, but was abolished by quenching betagamma subunits with specific intracellular peptides. Intracellular dialysis of G-protein betagamma subunits did not mimic the action of mGluR7, suggesting that both G-protein betagamma and alphao subunits were required to mediate the effect. Inhibition of phospholipase C (PLC) blocked the inhibitory action of mGluR7, suggesting that a coincident activation of PLC by the G-protein betagamma with alphao subunits was required. The Ca(2+) chelator BAPTA, as well as inhibition of either the inositol trisphosphate (IP(3)) receptor or protein kinase C (PKC) abolished the mGluR7 effect. Moreover, activation of native mGluR7 induced a PTX-dependent IP(3) formation. These results indicated that IP(3)-mediated intracellular Ca(2+) release was required for PKC-dependent inhibition of the Ca(2+) channels. Possible control of synaptic transmission by the present mechanisms is discussed.
尽管代谢型谷氨酸受体7（mGluR7）的突触前定位已得到充分证实，但该受体调控神经元中Ca(2+)通道的机制仍不清楚。我们在此表明，培养的小脑颗粒细胞在神经突起中表达天然代谢型谷氨酸受体7（mGluR7），而转染的mGluR7也在细胞体中表达。这使我们能够研究转染受体对体细胞Ca(2+)通道的影响。在转染的神经元中，mGluR7选择性抑制P/Q型Ca(2+)通道。该效应被GTPγS模拟，并被百日咳毒素（PTX）或针对G蛋白αo亚基产生的选择性抗体阻断，表明涉及一种类似G(o)的蛋白。mGluR7的效应未表现出G蛋白βγ亚基与α1A Ca(2+)通道亚基之间直接相互作用的特征，但通过用特定细胞内肽淬灭βγ亚基而被消除。细胞内透析G蛋白βγ亚基并未模拟mGluR7的作用，表明G蛋白βγ和αo亚基都需要介导该效应。抑制磷脂酶C（PLC）可阻断mGluR7的抑制作用，表明需要G蛋白βγ与αo亚基同时激活PLC。Ca(2+)螯合剂BAPTA以及抑制肌醇三磷酸（IP(3)）受体或蛋白激酶C（PKC）均可消除mGluR7的效应。此外，激活天然mGluR7可诱导PTX依赖性的IP(3)形成。这些结果表明，IP(3)介导的细胞内Ca(2+)释放是PKC依赖性抑制Ca(2+)通道所必需的。本文讨论了通过当前机制对突触传递进行可能调控的问题。
