Muscimol potentiation of acidic amino acid release from cerebellar synaptosomes is chloride dependent.

In previous studies we have shown that the depolarization-induced release of preaccumulated acidic amino acids and newly synthesized glutamate from cerebellar synaptosomal preparations is potentiated by gamma-aminobutyric acid (GABA) agonists through a GABAergic presynaptic mechanism. Here we report a systematic analysis of the ionic requirements of the potentiating effect of muscimol on the high K+-evoked release of D-[3H]aspartate. Our studies show that: Ca2+, Na+, and Mg2+ are not required for muscimol to exert its effect; a depolarizing concentration of K+ is a necessary, but not sufficient, condition to observe the presynaptic effect in question; and a minimal Cl- concentration (50-70 mM) is also required. A possible model based on these findings is proposed.