Evidence for cooperativity between neurons and astroglia in the regulation of CO2 fixation in vitro

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.