Department of Pharmacology and Physiology, University of Rochester Medical Center, Box 711, 601 Elmwood Avenue, Rochester, NY 14642, USA.
Eur J Pharmacol. 2010 Feb 10;627(1-3):63-8. doi: 10.1016/j.ejphar.2009.10.051. Epub 2009 Oct 30.
Recent studies indicate that the intracellular C-terminus of Group I metabotropic glutamate receptors (mGlu(1) and mGlu(5) receptor) is important in G protein coupling. To determine the necessity of the C-tail, a deletion mutant of mGlu(1) receptor was constructed, which included the first 840 amino acids of the rat mGlu(1a) receptor (mGlu(1)-dCT). G protein coupling of the receptors was assessed by measuring glutamate mediated inhibition of native calcium currents when each receptor was expressed in isolated sympathetic neurons from the rat superior cervical ganglion. Wild type mGlu(1) receptor activates both the Galpha(i/o) and Galpha(q/11) protein families. Each pathway can be detected in superior cervical ganglion neurons as voltage dependent and voltage independent inhibition of the calcium currents, respectively. While wild type mGlu(1) receptor gave rise to a strong, mixed voltage dependent and independent calcium current inhibition, mGlu(1)-dCT exhibited a weaker inhibition that was strongly voltage dependent, indicating activation of Galpha(i/o) was predominant. Further, pertussis toxin treatment reduced the inhibition by wild type mGlu(1) receptor to a smaller, voltage independent inhibition as expected, but completely abolished signaling through mGlu(1)-dCT. Finally, to test whether mGlu(1)-dCT could produce any activation of Galpha(q/11), inhibition of the native superior cervical ganglion M-type potassium currents was examined. M-channels, inhibited by PIP(2) depletion, were strongly inhibited by glutamate in cells expressing wild type mGlu(1) receptor, but no inhibition was detectable in neurons expressing mGlu(1)-dCT. These data indicate that C-terminal deletion of mGlu(1) receptor selectively abolishes Galpha(q/11) coupling.
最近的研究表明，I 型代谢型谷氨酸受体（mGlu(1) 和 mGlu(5) 受体）的细胞内 C 末端在 G 蛋白偶联中很重要。为了确定 C 尾的必要性，构建了 mGlu(1) 受体的缺失突变体，该突变体包含大鼠 mGlu(1a) 受体（mGlu(1)-dCT）的前 840 个氨基酸。通过测量每个受体在从大鼠颈上神经节分离的交感神经元中表达时谷氨酸介导的天然钙电流的抑制来评估受体的 G 蛋白偶联。野生型 mGlu(1) 受体激活 Galpha(i/o) 和 Galpha(q/11) 蛋白家族。这两种途径都可以在颈上神经节神经元中检测到，分别作为钙电流的电压依赖性和电压非依赖性抑制。虽然野生型 mGlu(1) 受体引起强烈的、混合的电压依赖性和非依赖性钙电流抑制，但 mGlu(1)-dCT 表现出较弱的抑制作用，强烈依赖于电压，表明 Galpha(i/o) 的激活占主导地位。此外，百日咳毒素处理将野生型 mGlu(1) 受体的抑制作用降低到较小的、电压非依赖性抑制作用，如预期的那样，但完全消除了 mGlu(1)-dCT 的信号传递。最后，为了测试 mGlu(1)-dCT 是否可以产生任何 Galpha(q/11) 的激活，检查了对天然颈上神经节 M 型钾电流的抑制作用。通过 PIP(2) 耗竭抑制的 M 通道在表达野生型 mGlu(1) 受体的细胞中被谷氨酸强烈抑制，但在表达 mGlu(1)-dCT 的神经元中没有检测到抑制作用。这些数据表明，mGlu(1) 受体的 C 末端缺失选择性地消除了 Galpha(q/11) 偶联。
