Uptake of glutamate, GABA, and glutamine into a predominantly GABA-ergic and a predominantly glutamatergic nerve cell population in culture.

Uptake kinetics for glutamate, GABA, and glutamine were determined in primary cultures of cerebral neurons, a predominantly GABA-ergic cell population, and of cerebellar granule cells, a predominantly glutamatergic cell population. A specially high Vmax for GABA uptake into the former and for glutamate uptake into the latter cells suggests that considerable amounts of released transmitters may be reaccumulated into appropriate nerve terminals. Nevertheless, the glutamate uptake into the cerebellar granule cells was less intense than that previously observed into corresponding cultures of astrocytes, whereas GABA was accumulated more intensely into neurons than into astrocytes. This suggests that especially glutamatergic neurons may be depleted for their transmitter by accumulation into adjacent astrocytes. If a glutamine flow astrocytes back to neurons served the purpose of balancing this transfer, it should be expected that glutamine accumulation was more intense in the glutamatergic than in the GABA-ergic cell population. This was not the case, suggesting that such a glutamate-glutamine cycle may not be operating to a major extent.