Lee Gwanwoo, Huang Yueming, Washington Jacqueline M, Briggs Nicole W, Zuo Zhiyi
Department of Anesthesiology, University of Virginia, Charlottesville, VA 22908, USA.
Epilepsy Res. 2005 Aug-Sep;66(1-3):145-53. doi: 10.1016/j.eplepsyres.2005.08.003.
Glutamate transporters (also called excitatory amino acid transporters, EAAT) participate in maintaining extracellular homeostasis of glutamate, a major excitatory neurotransmitter, and regulating glutamate neurotransmission. EAAT3, the major neuronal EAAT, may also regulate gamma-aminobutyric acid-mediated inhibitory neurotransmission. Dysfunction of EAAT3 has been shown to induce seizure in rats. We hypothesize that carbamazepine, a commonly used antiepileptic agent, enhances EAAT3 activity. We tested this hypothesis using oocytes artificially expressing EAAT3 and C6 rat glioma cells expressing endogenous EAAT3. In oocytes, carbamazepine dose-dependently enhanced EAAT3 activity. The EC50 of this carbamazepine effect was 12.2muM. The concentrations of carbamazepine to significantly enhance EAAT3 activity were within the therapeutic serum levels (17-51muM) of carbamazepine for the antiepileptic effect. Carbamazepine decreased the Km but did not change the maximal response of EAAT3 to glutamate. Carbamazepine-increased EAAT3 activity was inhibited by wortmannin or LY-294002, phosphatidylinositol 3-kinase (PI3K) inhibitors, but was not affected by staurosporine, chelerythrine or calphostin C, protein kinase C inhibitors. In C6 cells, carbamazepine also enhanced the endogenous EAAT3 activity. However, carbamazepine did not affect the activity of EAAT4 expressed in Cos7 cells. These results suggest that carbamazepine at clinically relevant concentrations specifically enhances the affinity of EAAT3 for glutamate to increase EAAT3 activity via a PI3K-dependent pathway. EAAT3 may be a therapeutic target for carbamazepine in the central nervous system.
谷氨酸转运体（也称为兴奋性氨基酸转运体，EAAT）参与维持主要兴奋性神经递质谷氨酸的细胞外稳态，并调节谷氨酸能神经传递。EAAT3是主要的神经元EAAT，也可能调节γ-氨基丁酸介导的抑制性神经传递。已证明EAAT3功能障碍会诱发大鼠癫痫发作。我们假设常用的抗癫痫药物卡马西平可增强EAAT3活性。我们使用人工表达EAAT3的卵母细胞和表达内源性EAAT3的C6大鼠胶质瘤细胞来验证这一假设。在卵母细胞中，卡马西平剂量依赖性地增强了EAAT3活性。这种卡马西平效应的半数有效浓度（EC50）为12.2μM。显著增强EAAT3活性的卡马西平浓度处于卡马西平抗癫痫作用的治疗血清水平（17 - 51μM）范围内。卡马西平降低了EAAT3对谷氨酸的米氏常数（Km），但未改变其对谷氨酸的最大反应。wortmannin或LY - 294002（磷脂酰肌醇3激酶（PI3K）抑制剂）可抑制卡马西平增加的EAAT3活性，但不受蛋白激酶C抑制剂星形孢菌素、白屈菜红碱或钙泊三醇的影响。在C6细胞中，卡马西平也增强了内源性EAAT3活性。然而，卡马西平不影响在Cos7细胞中表达的EAAT4的活性。这些结果表明，临床相关浓度的卡马西平通过PI3K依赖性途径特异性增强EAAT3对谷氨酸的亲和力，从而增加EAAT3活性。EAAT3可能是卡马西平在中枢神经系统中的治疗靶点。
