Author(s):
Gonçalves, Paula P. 
; Meireles, Sandra M. ; Neves, Paulo ; Vale, M. Graça P.
Date: 2001
Persistent ID: http://hdl.handle.net/10316/7857
Origin: Estudo Geral - Universidade de Coimbra
Document details
Ca2+ Sensitivity of Synaptic Vesicle Dopamine, ?-Aminobutyric Acid, and Glutama...
Description
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. http://dx.doi.org/10.1023/A:1007684716964
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. http://dx.doi.org/10.1023/A:1007684716964
Document Type
Article
Language English
Language English
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