Glutamate uptake by rat brain astroglia incubated in human cerebrospinal fluid

Abstract

Background: The glial compartment is critical for the regulation of glutamate concentration within the extracellular space. Reportedly, several factors influence glutamate uptake and metabolism in rat astroglia, which also appears to be affected by regional variables. In vitro, glutamate uptake by astroglia grown and tested in artificial media is affected by extracellular potassium. This report analyzes glutamate uptake by astroglia tested in a physiological extracelullar medium, cerebrospinal fluid (CSF), instead of artificial media.

Material/methods: Astroglial enriched subcultures of fronto-parietal cerebral cortex and striatum from 5-day-old rat pups were used to study glutamate uptake, using human CSF as the extracellular medium.

Result: Cultured astrocytes display significant glutamate uptake. This uptake is increased if the potassium concentration is elevated from 3.45 to 12.0 mM in culture medium, but not in the presence of CSE Differential effects of the glial inhibitor L-alpha-aminoadipic acid (L-alpha-AA) were observed at high concentrations in the presence of CSF, compared with standard incubation conditions. This was not observed when D-aspartate was used as a specific uptake competitor, suggesting that changes mediated by the presence of CSF components may not be directly linked to the primary transport mechanism, but could interfere at a more non-specific level.

Conclusions: These results confirm data from previous work on regional astroglial differences in glutamatergic management. Yet increased glutamate uptake following changes in extracellular potassium concentration depended on the nature of the culture medium used, since replacement of artificial culture medium by CSF resulted in no such increase.