Energy Coupling of L-Glutamate Transport and Vacuolar H+-ATPf in Brain Synaptic Vesicles1

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Abstract
Energy coupling of L-glutamate transport in brain synaptic vesicles has been studied. ATP-dependent acidification of the bovine brain synaptic vesicles was shown to require Cl−, to be accelerated by valinomycin and to be abolished by ammonium sulfate, nigericin or CCCP plus valinomycin, and K+. On the other hand, ATP-driven formation of a membrane potential (positive inside) was found to be stimulated by ammonium sulfate, not to be affected by nigericin and to be abolished by CCCP plus valinomycin and K+. Like formation of a membrane potential, ATP-dependent L-[3H]glutamate uptake into vesicles was stimulated by ammonium sulfate, not affected by nigericin and abolished by CCCP plus valinomycin and K+. The L- [3H]glutamate uptake differed in specificity from the transport system in synaptic plasma membranes. Both ATP-dependent H+ pump activity and L-glutamate uptake were inhibited by bafilomycin and cold treatment (common properties of vacuolar H-ATPase). ATP-dependent acidification in the presence of L-glutamate was also observed, suggesting that L-glutamate uptake lowered the membrane potential to drive further entry of H+. These results were consistent with the notion that the vacuolar H+-ATPase of synaptic vesicles formed a membrane potential to drive L-glutamate uptake. ATPase activity of the vesicles was not affected by the addition of Cl−, glutamate or nigericin, indicating that an electrochemical H+ gradient had no effect on the ATPase activity.

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