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Title: Ca2+ Sensitivity of Synaptic Vesicle Dopamine, ?-Aminobutyric Acid, and Glutamate Transport Systems
Authors: Gonçalves, Paula P. 
Meireles, Sandra M. 
Neves, Paulo 
Vale, M. Graça P. 
Issue Date: 2001
Citation: Neurochemical Research. 26:1 (2001) 75-81
Abstract: The effect of Ca2+ on the uptake of neurotransmitters by synaptic vesicles was investigated in a synaptic vesicle enriched fraction isolated from sheep brain cortex. We observed that dopamine uptake, which is driven at expenses of the proton concentration gradient generated across the membrane by the H+-ATPase activity, is strongly inhibited (70%) by 500 µM Ca2+. Conversely, glutamate uptake, which essentially requires the electrical potential in the presence of low Cl- concentrations, is not affected by Ca2+, even when the proton concentration gradient greatly contributes for the proton electrochemical gradient. These observations were checked by adding Ca2+ to dopamine or glutamate loaded vesicles, which promoted dopamine release, whereas glutamate remained inside the vesicles. Furthermore, similar effects were obtained by adding 150 µM Zn2+ that, like Ca2+, dissipates the proton concentration gradient by exchanging with H+. With respect to ?-aminobutyric acid transport, which utilizes either the proton concentration gradient or the electrical potential as energy sources, we observed that Ca2+ or Zn2+ do not induce great alterations in the ?-aminobutyric acid accumulation by synaptic vesicles. These results clarify the nature of the energy source for accumulation of main neurotransmitters and suggest that stressing concentrations of Ca2+ or Zn2+ inhibit the proton concentration gradient-dependent neurotransmitter accumulation by inducing H+ pump uncoupling rather than by interacting with the neurotransmitter transporter molecules.
DOI: 10.1023/A:1007684716964
Rights: openAccess
Appears in Collections:FCTUC Ciências da Vida - Artigos em Revistas Internacionais

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