McKenna Mary C
Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
J Neurosci Res. 2007 Nov 15;85(15):3347-58. doi: 10.1002/jnr.21444.
Although glutamate is usually thought of as the major excitatory neurotransmitter in brain, it is important to note that glutamate has many other fates in brain, including oxidation for energy, incorporation into proteins, and formation of glutamine, gamma-aminobutyric acid (GABA), and glutathione. The compartmentation of glutamate in brain cells is complex and modulated by the presence and concentration of glutamate per se as well as by other metabolites. Both astrocytes and neurons distinguish between exogenous glutamate and glutamate formed endogenously from glutamine via glutaminase. There is evidence of multiple subcellular compartments of glutamate within both neurons and astrocytes, and the carbon skeleton of glutamate can be derived from other amino acids and many energy substrates including glucose, lactate, and 3-hydroxybutyrate. Both astrocytes and neurons utilize glutamate, albeit for cell-specific metabolic fates. Glutamate is readily formed in neurons from glutamine synthesized in astrocytes, released into the extracellular space, and taken up by neurons. However, the glutamate-glutamine cycle is not a stoichiometric cycle but rather an open pathway that interfaces with many other metabolic pathways to varying extents depending on cellular requirements and priorities.
尽管谷氨酸通常被认为是大脑中的主要兴奋性神经递质，但需要注意的是，谷氨酸在大脑中还有许多其他去向，包括氧化供能、掺入蛋白质以及形成谷氨酰胺、γ-氨基丁酸（GABA）和谷胱甘肽。脑细胞中谷氨酸的区室化很复杂，受谷氨酸本身的存在和浓度以及其他代谢物的调节。星形胶质细胞和神经元都能区分外源性谷氨酸和通过谷氨酰胺酶由谷氨酰胺内源性形成的谷氨酸。有证据表明，神经元和星形胶质细胞内都存在多个谷氨酸亚细胞区室，谷氨酸的碳骨架可来自其他氨基酸以及许多能量底物，包括葡萄糖、乳酸和3-羟基丁酸。星形胶质细胞和神经元都利用谷氨酸，尽管其用于细胞特异性的代谢命运。谷氨酸很容易在神经元中由星形胶质细胞合成的谷氨酰胺形成，释放到细胞外空间，然后被神经元摄取。然而，谷氨酸-谷氨酰胺循环不是一个化学计量循环，而是一个开放途径，它与许多其他代谢途径在不同程度上相互作用，这取决于细胞的需求和优先级。
