Fillenz M
University Laboratory of Physiology, Oxford, UK.
Behav Brain Res. 1995 Nov;71(1-2):51-67. doi: 10.1016/0166-4328(95)00045-3.
The contribution of in vivo monitoring to the study of glutamate release is reviewed. Physiological stimulation increases both glutamate and aspartate in the extracellular compartment of the brain and both amino acids show Ca(2+)-dependent K(+)-evoked release. However, the finding that only glutamate is stored in synaptic vesicles implies that glutamate is the excitatory transmitter. Released glutamate is taken up into both neurones and glia by glutamate transporters. Uptake of glutamate, in addition to clearing the synapse, has a number of additional functions. Uptake into glia leads to the release of glutamine, which is involved in the recycling of transmitter glutamate; uptake into both neurones and glia leads to the release of ascorbate; uptake into glia leads to an increase glycolysis and export of lactate, an energy substrate for neuronal metabolism. Reversal of the glutamate transporter accounts for the parallel release of glutamate and aspartate from the cytoplasmic compartment. The basal concentration of extracellular glutamate is in the micromolar range. Such levels could lead to desensitisation of both NMDA and non-NMDA receptors. The functional implications of the level of basal glutamate are difficult to assess at present in view of the existence of multiple glutamate receptor subunits with different functional properties and distributions.
本文综述了体内监测对谷氨酸释放研究的贡献。生理刺激会增加大脑细胞外区室中的谷氨酸和天冬氨酸，且这两种氨基酸都表现出钙（2+）依赖性钾离子诱发释放。然而，只有谷氨酸储存在突触小泡中的这一发现表明谷氨酸是兴奋性神经递质。释放的谷氨酸通过谷氨酸转运体被神经元和神经胶质细胞摄取。谷氨酸的摄取除了清除突触外，还有许多其他功能。摄取到神经胶质细胞会导致谷氨酰胺的释放，谷氨酰胺参与神经递质谷氨酸的再循环；摄取到神经元和神经胶质细胞都会导致抗坏血酸的释放；摄取到神经胶质细胞会导致糖酵解增加和乳酸的输出，乳酸是神经元代谢的能量底物。谷氨酸转运体的反向转运导致谷氨酸和天冬氨酸从细胞质区室平行释放。细胞外谷氨酸的基础浓度在微摩尔范围内。这样的水平可能导致NMDA和非NMDA受体脱敏。鉴于存在具有不同功能特性和分布的多个谷氨酸受体亚基，目前很难评估基础谷氨酸水平的功能意义。
