Plested Andrew J R, Wildman Scott S, Lieb William R, Franks Nicholas P
Biophysics Section, The Blackett Laboratory, Imperial College London, London, United Kingdom.
Anesthesiology. 2004 Feb;100(2):347-58. doi: 10.1097/00000542-200402000-00025.
There is substantial and growing literature on the actions of general anesthetics on a variety of neurotransmitter-gated ion channels, with the greatest attention being focused on inhibitory gamma-amino butyric acid type A receptors. In contrast, glutamate receptors, the most important class of fast excitatory neurotransmitter-gated receptor channels, have received much less attention, and their role in the production of the anesthetic state remains controversial.
alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors formed from a variety of different subunits were expressed in Xenopus oocytes and HEK-293 cells, and their sensitivities to the inhalational general anesthetics xenon, isoflurane, and halothane were determined using two-electrode voltage clamp and patch clamp techniques. The effects of desensitization on anesthetic sensitivity were investigated using cyclothiazide and site-directed mutagenesis. An ultrarapid application system was also used to mimic rapid high-concentration glutamate release at synapses.
The authors show that xenon can potently inhibit AMPA receptors when assayed using bath application of kainate. However, when the natural neurotransmitter l-glutamate is used under conditions in which the receptor desensitization is blocked and the peak of the glutamate-activated response can be accurately measured, the pattern of inhibition changes markedly. When desensitization is abolished by a single-point mutation (L497Y in GluR1 and the equivalent mutation L505Y in GluR4), the xenon inhibition is eliminated. When AMPA receptors are activated by glutamate using an ultrarapid application system that mimics synaptic conditions, sensitivity to xenon, halothane, and isoflurane is negligible.
AMPA receptors, when assayed in heterologous expression systems, showed a sensitivity to inhalational anesthetics that was minimal when glutamate was applied rapidly at high concentrations. Because these are the conditions that are most relevant to synaptic transmission, the authors conclude that AMPA receptors are unlikely to play a major role in the production of the anesthetic state by inhalational agents.
关于全身麻醉药对多种神经递质门控离子通道作用的文献数量可观且不断增加，其中受到最多关注的是抑制性γ-氨基丁酸A型受体。相比之下，谷氨酸受体作为最重要的一类快速兴奋性神经递质门控受体通道，受到的关注要少得多，其在麻醉状态产生中的作用仍存在争议。
由多种不同亚基组成的α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）受体在非洲爪蟾卵母细胞和人胚肾293（HEK-293）细胞中表达，并使用双电极电压钳和膜片钳技术测定它们对吸入性全身麻醉药氙气、异氟烷和氟烷的敏感性。使用环噻嗪和定点诱变研究脱敏对麻醉敏感性的影响。还使用了超快速应用系统来模拟突触处快速高浓度谷氨酸的释放。
作者表明，当使用浴加应用 kainate 进行测定时，氙气可有效抑制AMPA受体。然而，当在受体脱敏被阻断且可准确测量谷氨酸激活反应峰值的条件下使用天然神经递质L-谷氨酸时，抑制模式会发生明显变化。当通过单点突变（GluR1中的L497Y和GluR4中的等效突变L505Y）消除脱敏时，氙气抑制作用消失。当使用模拟突触条件的超快速应用系统通过谷氨酸激活AMPA受体时，对氙气、氟烷和异氟烷的敏感性可忽略不计。
在异源表达系统中进行测定时，AMPA受体对吸入性麻醉药的敏感性在高浓度快速应用谷氨酸时最小。因为这些是与突触传递最相关的条件，作者得出结论，AMPA受体不太可能在吸入性药物产生麻醉状态中起主要作用。
