Comparison of the Properties of γ‐Aminobutyric Acid and L‐Glutamate Uptake into Synaptic Vesicles Isolated from Rat Brain

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Abstract
Rat brain synaptic vesicles exhibit ATP-dependent uptake of .gamma.-[3H]amino-n-butyric acid ([3H]GABA) and L-[3H]glutamate. After hypotonic shock, the highest specific activities of uptake of both L-glutamate and GABA were recovered in the 0.4 M fraction of a sucrose gradient. The uptakes of L-glutamate and GABA were inhibited by similar, but not identical, concentrations of the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone and the ionophores nigericin and gramicidin, but they were not inhibited by the K+ carrier valinomycin. N, N''-Dicyclohexylcarbodiimide and N-ethylmaleimide, Mg2+-ATPase inhibitors, inhibited the GABA and L-glutamate uptakes similarly. Low concentrations of Cl- stimulated the vesicular uptake of L-glutamate but not that of GABA. The uptakes or both L-glutamatate and GABA were inhibited by high concentration of Cl-. These results indicate that the vesicular GABA and L-glutamate uptakes are driven by an electrochemical protongradient generated by a similar Mg2+-ATPase. The vesicular uptake mechanisms are discussed in relation to other vesicle uptake systems.