Transport and binding of GABA and related amino acids by peripheral glial cells of dorsal root ganglia

Abstract

The isolated, de-sheathed dorsal root ganglion of the rat provides a useful model for the study of a number of aspects of glial cell function. GABA and glutamate are both actively accumulated with K m's of 9.7 and 20.6 μM and V max's of 2.6 and 5.9 nmol/min −1g −1, respectively. Uptake of these amino acids is temperature and energy dependent, and requires the presence of sodium ions in the medium. The uptake of GABA is potently inhibited by beta-alanine, a compound showing little activity on the neuronal uptake of GABA. Ganglia which have been pre-loaded with labelled GABA or glutamate exhibit an enhanced release when exposed to elevated K + but not veratridine; the release process is partially calcium-dependent. Studies on the release of endogenous amino acids from DRG's have consistently failed to demonstrate any increased release of either GABA or glutamate upon depolarization. Under release conditions where re-uptake is minimized, accumulated GABA readily exchanges with beta-alanine, 3-hydroxyGABA, nipecotic acid and, L-2,4-diaminobutyric acid. Isolated, extensively-washed whole DRG membranes will bind GABA in a specific Na +-dependent manner, and it is likely that this site is identical with the GABA transport recognition site.