RELEASE OF [³H]GAMMA‐AMINOBUTYRIC ACID FROM GLIAL CELLS IN RAT DORSAL ROOT GANGLIA.

Abstract

Abstract— Desheathed rat dorsal root ganglia were incubated in a medium containing amino‐oxyacetic acid and [ 3 H]GABA. Under these conditions, [ 3 H]GABA is taken up exclusively by the satellite glial cells in the ganglia. Efflux of [ 3 H]GABA from the tissue was measured after passing the ganglia through a series of wash solutions. The spontaneous efflux of radioactivity, mostly [ 3 H]GABA, was more rapid in the absence of amino‐oxyacetic acid in the incubation and wash media. Raising the potassium concentration in the wash media caused an increase in the efflux of [ 3 H]GABA. This increase was sigmoidally related to the potassium concentration in the wash media, reaching a maximum at 64 m m ‐K + . The releasing effect of K + was inhibited by removing calcium from the media. Reducing the calcium and raising the magnesium concentration in the wash solutions inhibited the increased efflux of [ 3 H]GABA due to 64 m m ‐K + by 48 per cent, while 5 mM‐La 3+ and diphenylhydantoin (0·005 and 0·5 m m ) had no effect on this increase. Only a small increase in the efflux of [ 14 C]glutamate was produced by 64 m m ‐K + and it had no effect upon the effluxes of [ 3 H]glycine, [ 3 H]alanine or [ 3 H]leucine. The efflux of lactate dehydrogenase was similarly unaffected by 64 mM‐K + . The results suggest that glial cells in spinal ganglia can respond to depolarizing concentrations of potassium by releasing GABA in a calcium‐dependent process.