3-Mercaptopropionic acid inhibits GABA release from rat brain slices in vitro

3-Mercaptopropionic acid (3MP) (1 mM) inhibited the potassium-evoked release of endogenous GABA from slices of rat hippocampus and cerebral cortex in vitro. This did not appear to be due to an inhibition of GABA biosynthesis, since 3MP failed to affect the basal rate of GABA release or to accelerate the decline in the GABA content of tissue slices during prolonged exposure to 3MP (up to 120 min). 3MP, furthermore, inhibited the potassium-evoked release of [3H]GABA from preloaded brain slices, suggesting a direct inhibitory effect on GABA release. The threshold concentration was approximately 0.1 mM. 3MP at 1 mM failed to inhibit the potassium-evoked release of [3H]5-hydroxytryptamine, [3H]noradrenaline or somatostatin under similar conditions. The ability of 3MP to inhibit GABA release may contribute to the convulsant properties of this substance in vivo.