Glutamine efflux from astrocytes is mediated by multiple pathways
Glutamine efflux from astrocytes is mediated by multiple pathways
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DOI：
10.1046/j.1471-4159.2003.01981.x
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发表时间：
2003-10-01
影响因子：
4.7
通讯作者：
Bröer, S
中科院分区：
文献类型：
--
作者：
Deitmer, JW;Bröer, A;Bröer, S
神经递质谷氨酸一旦释放到突触间隙中，就主要通过谷氨酸-谷氨酰胺循环再循环，其涉及摄取到星形胶质细胞中，转化为谷氨酰胺，随后从星形胶质细胞释放谷氨酰胺作为神经元谷氨酸合成的前体。我们分析了从培养的星形胶质细胞的谷氨酰胺流出预加载细胞标记谷氨酰胺30分钟，随后测量谷氨酰胺流出30分钟。流出预加载的谷氨酰胺是快速的，几乎完全后30分钟，一级速率为0.11 +/- 0.01/min。流出减少50%时，细胞内的Na+耗尽。增加细胞内Na+浓度对谷氨酰胺外排有小的刺激作用，表明Na+依赖性转运机制的参与。约50%的基础外排不能被细胞内Na+的耗竭抑制，表明存在额外的Na+非依赖性转运机制。谷氨酰胺外排刺激两到三倍，通过添加细胞外中性氨基酸，如丙氨酸或亮氨酸。丙氨酸和亮氨酸的刺激作用有一个Na+依赖和Na+独立的组件，这表明存在两个反向转运机制之一，涉及Na+。当与培养的星形胶质细胞中谷氨酰胺转运蛋白mRNA的表达相比时，谷氨酰胺外排似乎可能由SN 1、LAT 2、ASCT 2和另外的尚未鉴定的转运蛋白介导，该转运蛋白介导约40%的基础外排。
The neurotransmitter glutamate, once released into the synaptic cleft, is largely recycled by the glutamate - glutamine cycle, which involves uptake into astrocytes, conversion into glutamine and subsequent release of glutamine from astrocytes as a precursor for neuroneal glutamate synthesis. We analysed glutamine efflux from cultured astrocytes by pre-loading cells with labelled glutamine for 30 min and subsequently measured glutamine efflux for 30 min. Efflux of preloaded glutamine was rapid and almost complete after 30 min with a first order rate of 0.11 +/- 0.01/min. Efflux was 50% reduced when cells were depleted of intracellular Na+. Increasing intracellular Na+ concentration had a small stimulatory effect on glutamine efflux, indicating the participation of a Na+-dependent transport mechanism. About 50% of the basal efflux could not be inhibited by depletion of the intracellular Na+, suggesting the presence of an additional Na+-independent transport mechanism. Glutamine efflux was stimulated two- to threefold by addition of extracellular neutral amino acids, such as alanine or leucine. The stimulatory effects of alanine and leucine had a Na+-dependent and a Na+- independent component, suggesting the presence of two antiport mechanisms one involving Na+. When compared to the expression of glutamine transporter mRNAs in cultured astrocytes it appeared likely that glutamine efflux was mediated by SN1, LAT2, ASCT2 and an additional, yet unidentified, transporter that mediates about 40% of the basal efflux.