MECHANISM ON REGULATION OF EXTRACELLULAR EXCESSIVE AMOUNTS OF GLUTAMIC-ACID IN THE CULTURED BRAIN NEURONAL AND GLIAL-CELLS

In order to search for the mechanism which maintains the amounts of extracellular glutamate (Glu) in cultured glia-rich and -poor rat cerebellar granule cells under normal and acidosis conditions the alteration of extra- and intra-cellular Glu and glutamine (Gln) levels after the treatment of a large amount of Glu were quantified by means of the HPLC-ECD with a newly developed microdialysis method. Within thirty minutes after exposure to excessive amounts of Glu (50 muM) under normal conditions in a glia-rich culture, the extra-cellular Glu levels showed a rapid decrease and the extracellular levels of Gln steeply increased compared to those seen in a glia-poor culture. Under the acidosis (pH 7.2) conditions, a significant increase of extra cellular Glu levels was detected after a treatment of 0.5 hrs, although intracellular Glu levels and both extra-and intracellular Gln levels did not appear to have changed significantly. Additionally glutamine synthetase activity did not change under the acidosis condition. The more remarkable increase of Glu levels were detected after the treatment of excessive amounts of Glu. And its sustained increase was much higher than those seen under normal conditions. The magnitude of this increase was detected as larger in a glia-poor cell culture than in a glia-rich one. These results suggest that the Glu uptake system in glia cells might be important in regulating the extracellular Glu levels in the central nervous system.