吸人麻醉药减轻氧化应激反应对EAAT3活性的抑制效应

背景谷氨酸转运体3（也叫做兴奋性氨基酸转运体3，EAAT3）是-种重要的神经元EAAT，吸入麻醉剂能增强其活性。除了谷氨酸，EAAT3还能摄取L-半胱氨酸——谷胱甘肽合成的限速底物。我们前期的研究表明氧化应激反应能抑制EAAT3对谷氨酸的转运，本研究的目的是为了确定氧化应激反应是否能够抑制半胱氨酸诱导的EAAT3的活性，以及吸入性麻醉剂是否能够减轻这种抑制作用。方法在爪蟾的卵细胞内表达大鼠EAAT3。用双电极电压钳技术记录L-谷氨酸和L-半胱氨酸产生的膜电流。根据EAATs转运底物能够生电这-原理，我们用膜电流的峰值来定量反应转运的底物的数量。结果将卵细胞暴露在-种有机氧化剂-5mmol／L的t-BHP（叔丁基过氧化氢）——中达10分钟，EAAT3转运L-半胱氨酸的Vmax降低，而其K。不受影响。浓度在l％～3％之间的吸入麻醉剂异氟烷、七氟烷、地氟烷能够减轻过氧化氢诱导的EAAT3对L-谷氨酸和L-半胱氨酸活性的抑制作用。结论我们的研究结果表明在氧化应激状态下，吸入性麻醉药维护了EAAT3转运L-谷氨酸和L-半胱氨酸的功能，这也许是吸入麻醉剂神经保护的一种机制。

BACKGROUND： Volatile anesthetics enhance the activity of glutamate transporter Type 3 （also called excitatory amino acid transporter Type 3, EAAT3）, the maior neuronal EAAT. In addition to glutamate, EAAT3 can also uptake L-cysteine, the rate-limiting substrate for the synthesis of glutathione. Our previous study showed that oxidative stress inhibited glutamate-induced EAAT3 activity. We determined whether oxidative stress would reduce L-cysteine- induced EAAT3 activity and whether this reduction would be attenuated by volatile anesthetics. METHODS： Rat EAAT3 was expressed in Xenopus oocytes. L-glutamate- and L-cysteine-induced membrane currents were recorded using the 2-electrode voltage clamp technique. The peak current was quantified to reflect the amount of transported substrates because transport of substrates via EAATs is electrogenic. RESULTS： Exposure of oocytes to 5 mM tert-butyl bydroperoxide, an organic oxidant, for 10 rain reduced the V^ax, but did not affect the Kin, of EAAT3 for L-cysteine. The volatile anesthetics isoflurane, sevoflurane, and desflurane at concentrations from 1% to 3% attenuated the tert- butyl hydroperoxide-reduced EAAT3 activity for L-glutamate and L-cysteine. CONCLUSIONS： Our results suggest that volatile anesthetics preserve EAAT3 function to transport l-glutamate and l-cysteine under oxidative stress, which may be a mechanism for the neuroprotective effects of volatile anesthetics.