Cornelison Garrett L, Daszkowski Anna W, Pflanz Natasha C, Mihic S John
Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, Texas.
Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, Texas
J Pharmacol Exp Ther. 2017 Apr;361(1):1-8. doi: 10.1124/jpet.116.239152. Epub 2017 Jan 13.
The glycine receptor is a pentameric ligand-gated ion channel that is involved in fast inhibitory neurotransmission in the central nervous system. Zinc is an allosteric modulator of glycine receptor function, enhancing the effects of glycine at nanomolar to low-micromolar concentrations and inhibiting its effects at higher concentrations. Low-nanomolar concentrations of contaminating zinc in electrophysiological buffers are capable of synergistically enhancing receptor modulation by other compounds, such as ethanol. This suggests that, unless accounted for, previous studies of glycine receptor modulation were measuring the effects of modulator plus comodulation by zinc on receptor function. Since zinc is present in vivo at a variety of concentrations, it will influence glycine receptor modulation by other pharmacologic agents. We investigated the utility of previously described "zinc-enhancement-insensitive" 1 glycine receptor mutants D80A, D80G, and W170S to probe for interactions between zinc and other allosteric modulators at the glycine receptor. We found that only the W170S mutation conferred complete abolishment of zinc enhancement across a variety of agonist and zinc concentrations. Using 1 W170S receptors, we established that, in addition to ethanol, zinc interacts with inhalants, but not volatile anesthetics, to synergistically enhance channel function. Additionally, we determined that this interaction is abolished at higher zinc concentrations when receptor-enhancing binding sites are saturated, suggesting a mechanism by which modulators such as ethanol and inhalants are capable of increasing receptor affinity for zinc, in addition to enhancing channel function on their own.
甘氨酸受体是一种五聚体配体门控离子通道，参与中枢神经系统的快速抑制性神经传递。锌是甘氨酸受体功能的变构调节剂，在纳摩尔至低微摩尔浓度下增强甘氨酸的作用，而在较高浓度下抑制其作用。电生理缓冲液中低纳摩尔浓度的污染锌能够协同增强其他化合物（如乙醇）对受体的调节作用。这表明，除非加以考虑，先前关于甘氨酸受体调节的研究测量的是调节剂加上锌的共调节对受体功能的影响。由于锌在体内以多种浓度存在，它将影响其他药物对甘氨酸受体的调节。我们研究了先前描述的“锌增强不敏感”甘氨酸受体突变体D80A、D80G和W170S在探测锌与甘氨酸受体上其他变构调节剂之间相互作用方面的效用。我们发现，只有W170S突变在各种激动剂和锌浓度下都能完全消除锌增强作用。使用W170S受体，我们确定，除了乙醇外，锌还与吸入剂相互作用，但不与挥发性麻醉剂相互作用，以协同增强通道功能。此外，我们还确定，当受体增强结合位点饱和时，这种相互作用在较高锌浓度下会被消除，这表明乙醇和吸入剂等调节剂除了自身增强通道功能外，还能够增加受体对锌的亲和力的一种机制。
