Kaufman E E, Driscoll B F
Laboratory of Cerebral Metabolism, National Institute of Mental Health, Bethesda 20892.
Dev Neurosci. 1993;15(3-5):299-305. doi: 10.1159/000111348.
Increases in the extracellular potassium concentration which correspond to the increased potassium concentration seen with both normal and abnormal neuronal stimulation produce marked increases in the rate of CO2 fixation in astroglial cells in primary culture. This increase in CO2 fixation is seen only in astroglial cells; the low rate of CO2 fixation seen in the neurons did not respond to the increased potassium concentration. Cultures of astroglia and mixed astroglia-neurons were labeled with NaH[14C]O3 for 20 h to obtain material for preliminary identification of the labeled products of CO2 fixation in the extracellular and intracellular compartments. While both cultures had similar intracellular levels of labeled products (mainly amino acids), astroglial cultures released 4-fold more labeled products into the extracellular fluid. While labeled glutamine is a prominent product of astroglia, the bulk of the released labeled products are nonamino acids. These are presumably the products available to be recycled back to surrounding neurons (which cannot fix CO2) to replenish intermediates of the TCA cycle lost due to release of the neurotransmitters glutamate, aspartate and GABA.
细胞外钾离子浓度的升高，这与正常和异常神经元刺激时所见到的升高的钾离子浓度相对应，会使原代培养的星形胶质细胞中二氧化碳固定速率显著增加。这种二氧化碳固定的增加仅见于星形胶质细胞；神经元中较低的二氧化碳固定速率对升高的钾离子浓度没有反应。用NaH[14C]O3标记星形胶质细胞培养物和星形胶质细胞-神经元混合培养物20小时，以获取用于初步鉴定细胞外和细胞内区室中二氧化碳固定标记产物的材料。虽然两种培养物的细胞内标记产物水平相似（主要是氨基酸），但星形胶质细胞培养物向细胞外液中释放的标记产物多4倍。虽然标记的谷氨酰胺是星形胶质细胞的主要产物，但释放的大部分标记产物是非氨基酸。这些产物大概可循环回到周围的神经元（其不能固定二氧化碳），以补充因神经递质谷氨酸、天冬氨酸和γ-氨基丁酸的释放而损失的三羧酸循环中间产物。
