Evidence for net uptake of GABA into mouse astrocytes in primary cultures--its sodium dependence and potassium independence

Abstract

Content of GABA was measured in cultured, normal astrocytes [from the brain cortex of newborn mice] together with the effect of nonradioactive GABA on the efflux of labeled GABA from cells previously loaded with (14C)GABA. An increase of external GABA concentration from 0 to 25 micron evoked a rise of the GABA content in the cells to a level which was approximately 50 times that of the incubation medium. Neither 200 nor 2000 micron nonradioactive GABA had any effect on the rate of release of radioactivity from cells loaded with (14C)GABA. Both the high tissue/medium ratio and the lack of a GABA-induced enhancement of the release of radioactivity indicate that the previously observed high-affinity uptake of GABA in cultured astrocytes represents a net uptake and not a homoexchange with endogenous GABA. This uptake is sodium dependent but was found to be unaffected in potassium-free media; the quantitative correlation between GABA transport and sodium transport differed from that reported for synaptosomes.