Jin Chun, Smothers C Thetford, Woodward John J
Department of Neurosciences and Center for Drug and Alcohol Programs, Medical University of South Carolina, Charleston, South Carolina.
Alcohol Clin Exp Res. 2008 Jun;32(6):1059-66. doi: 10.1111/j.1530-0277.2008.00667.x. Epub 2008 Apr 26.
The effects of ethanol on brain function are thought to be partly because of altered activity of ion channels that regulate synaptic activity. Results from previous studies from this lab and others have shown that ethanol inhibits the function of the N-methyl-D-aspartate (NMDA) receptors, a calcium-permeable ion channel activated by the neurotransmitter glutamate. Factors that influence the acute sensitivity of NMDA receptors to ethanol may be critical in determining how neurons and neuronal networks respond to the presence of ethanol. In this study, we have examined the effect of physiologically relevant concentrations of magnesium on the ethanol sensitivity of recombinant NMDA receptors and how ethanol inhibition under these conditions is influenced by the NR3A subunit.
Recombinant cDNAs encoding NMDA receptor subunits were expressed in human embryonic kidney 293 cells. Whole-cell patch-clamp electrophysiology was used to measure currents induced by rapid application of glutamate in the absence and presence of ethanol.
In magnesium-free recording solution, ethanol inhibited glutamate-mediated currents in cells transfected with NMDA receptor subunits. The magnitude of ethanol inhibition was significantly enhanced when recordings were carried out in media containing 1 mM magnesium. This effect was reversible and required magnesium-sensitive receptors. Magnesium did not enhance ethanol inhibition of glycine-activated NR1/NR3A/NR3B receptors. However, NR3A co-expression prevented the enhancement of ethanol's inhibitory effect on receptors composed of NR2A but not NR2B subunits.
These results suggest that under physiological conditions, NR3A may be an important regulator of the acute ethanol sensitivity of brain NMDA receptors.
乙醇对脑功能的影响被认为部分是由于调节突触活动的离子通道活性改变所致。本实验室及其他实验室之前的研究结果表明，乙醇会抑制N-甲基-D-天冬氨酸（NMDA）受体的功能，NMDA受体是一种由神经递质谷氨酸激活的钙通透性离子通道。影响NMDA受体对乙醇急性敏感性的因素可能对确定神经元和神经网络对乙醇存在的反应方式至关重要。在本研究中，我们研究了生理相关浓度的镁对重组NMDA受体乙醇敏感性的影响，以及在这些条件下乙醇抑制作用如何受NR3A亚基的影响。
编码NMDA受体亚基的重组cDNA在人胚肾293细胞中表达。采用全细胞膜片钳电生理学方法，在不存在和存在乙醇的情况下，测量快速施加谷氨酸诱导的电流。
在无镁的记录溶液中，乙醇抑制了转染NMDA受体亚基的细胞中谷氨酸介导的电流。当在含有1 mM镁的培养基中进行记录时，乙醇抑制的幅度显著增强。这种效应是可逆的，且需要镁敏感受体。镁不会增强乙醇对甘氨酸激活的NR1/NR3A/NR3B受体的抑制作用。然而，NR3A共表达可防止乙醇对由NR2A而非NR2B亚基组成的受体的抑制作用增强。
这些结果表明，在生理条件下，NR3A可能是脑NMDA受体急性乙醇敏感性的重要调节因子。
