Ramaharobandro N, Borg J, Mandel P, Mark J
Brain Res. 1982 Jul 22;244(1):113-21. doi: 10.1016/0006-8993(82)90909-x.
The uptake of L-glutamine in neuronal and glial cultures derived from rat cerebral hemispheres was found to be mediated by a low affinity-high capacity mechanism which was concentrative in both cell types; the calculated Km and Vmax were twice as high in glial than in neuronal cultures. In contrast L-glutamate was taken up by a high affinity system which was particularly efficient and concentrative in the glial cells. Different transport mechanisms for L-glutamine appeared to operate in the two cell types: L-glutamine uptake in neurons was sodium-dependent, specifically inhibited by L-glutamine but not affected by high potassium concentrations in the external medium; on the other hand, glial glutamine transport was decreased when potassium concentration increased, was sodium-independent and significantly inhibited by 3 structurally related amino acids. No significant contribution of homoexchange could be detected in either cell type. After [14C]glutamine preincubation, the radioactivity released into the superfusion medium by neuronal cells was increased in the presence of a high potassium concentration; no such effect could be seen in the case of glial cultures. A regulatory mechanism is suggested where astrocyte depolarization and repolarization would channel a flux of glutamine toward the neurons, subsequent to a glutamate flux in the opposite direction.
研究发现，源自大鼠大脑半球的神经元和神经胶质细胞培养物对L-谷氨酰胺的摄取是由一种低亲和力-高容量机制介导的，这种机制在两种细胞类型中都是浓缩性的；计算得出神经胶质细胞培养物中的Km和Vmax是神经元培养物中的两倍。相比之下，L-谷氨酸是通过一种高亲和力系统摄取的，该系统在神经胶质细胞中特别有效且具有浓缩性。两种细胞类型中L-谷氨酰胺的转运机制似乎不同：神经元中L-谷氨酰胺的摄取依赖于钠， specifically inhibited by L-glutamine but not affected by high potassium concentrations in the external medium;另一方面，当钾浓度增加时，神经胶质细胞的谷氨酰胺转运减少，不依赖于钠，且受到3种结构相关氨基酸的显著抑制。在两种细胞类型中均未检测到同向交换的显著作用。用[14C]谷氨酰胺预孵育后，在高钾浓度存在的情况下，神经元细胞释放到灌流培养基中的放射性增加；在神经胶质细胞培养物中未观察到这种效应。有人提出一种调节机制，即星形胶质细胞去极化和复极化会在谷氨酸向相反方向流动之后，引导谷氨酰胺流向神经元。
