Mutkus Lysette, Aschner Judy L, Syversen Tore, Shanker Gouri, Sonnewald Ursula, Aschner Michael
Department of Physiology, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1083, USA.
Biol Trace Elem Res. 2006 Mar;109(3):267-80. doi: 10.1385/BTER:109:3:267.
Glutamate is removed mainly by astrocytes from the extracellular fluid via high-affinity astroglial Na+ -dependent excitatory amino acid transporters, glutamate/aspartate transporter (GLAST), and glutamate transporter-1 (GLT-1). Mercuric chloride (HgCl2) is a highly toxic compound that inhibits glutamate uptake in astrocytes, resulting in excessive extracellular glutamate accumulation, leading to excitotoxicity and neuronal cell death. The mechanisms associated with the inhibitory effects of HgCl2 on glutamate uptake are unknown. This study examines the effects of HgCl2 on the transport of 3H-D-aspartate, a nonmetabolizable glutamate analog, using Chinese hamster ovary cells (CHO) transfected with two glutamate transporter subtypes, GLAST (EAAT1) and GLT-1 (EAAT2), as a model system. Additionally, studies were undertaken to determine the effects of HgCl2 on mRNA and protein levels of these transporters. The results indicate that (1) HgCl2 leads to significant (p < 0.001) inhibition of glutamate uptake via both transporters, but is a more potent inhibitor of glutamate transport via GLAST and (2) the effect of HgCl2 on inhibition of glutamate uptake in transfected CHO cells is not associated with changes in transporter protein levels despite a significant decrease in mRNA expression; thus, (3) HgCl2 inhibition is most likely related to its direct binding to the functional thiol groups of the transporters and interference with their uptake function.
谷氨酸主要通过星形胶质细胞，经高亲和力的星形胶质细胞钠依赖性兴奋性氨基酸转运体、谷氨酸/天冬氨酸转运体（GLAST）和谷氨酸转运体-1（GLT-1）从细胞外液中清除。氯化汞（HgCl2）是一种剧毒化合物，可抑制星形胶质细胞对谷氨酸的摄取，导致细胞外谷氨酸过度积累，从而引发兴奋性毒性和神经元细胞死亡。HgCl2对谷氨酸摄取的抑制作用相关机制尚不清楚。本研究以转染了两种谷氨酸转运体亚型GLAST（EAAT1）和GLT-1（EAAT2）的中国仓鼠卵巢细胞（CHO）为模型系统，研究HgCl2对3H-D-天冬氨酸（一种不可代谢的谷氨酸类似物）转运的影响。此外，还进行了研究以确定HgCl2对这些转运体的mRNA和蛋白质水平的影响。结果表明：（1）HgCl2导致两种转运体对谷氨酸摄取的显著抑制（p < 0.001），但对通过GLAST的谷氨酸转运抑制作用更强；（2）尽管mRNA表达显著下降，但HgCl2对转染CHO细胞中谷氨酸摄取的抑制作用与转运体蛋白水平的变化无关；因此，（3）HgCl2抑制作用很可能与其直接结合转运体的功能性巯基并干扰其摄取功能有关。
