| Autor: |
Gonçalves PP; Centro de Biologia Celular, Departamento de Biologia, Universidade de Aveiro, 3810, Aveiro, Portugal. pgoncalves@biio.ua.pt, Meireles SM, Neves P, Vale MG |
| Jazyk: |
angličtina |
| Zdroj: |
Brain research. Molecular brain research [Brain Res Mol Brain Res] 1999 Aug 25; Vol. 71 (2), pp. 178-84. |
| DOI: |
10.1016/s0169-328x(99)00183-7 |
| Abstrakt: |
Synaptic vesicles isolated from sheep brain cortex accumulate Ca2+ by a mechanism of secondary active transport associated to the H(+)-pump activity. The process can be visualized either by measuring Ca(2+)-induced H+ release or DeltapH-dependent Ca2+ accumulation. We observed that the amount of Ca2+ taken up by the vesicles increases with the magnitude of the DeltapH across the membrane, particularly at Ca2+ concentrations (approximately 500 microM) found optimal for the antiporter activity. Similarly, H+ release induced by Ca2+ increased with the magnitude of DeltapH. However, above 60% DeltapH (high H(+)-pump activity), the net H+ release from the vesicles decreased as the pump-mediated H+ influx exceeded the Ca(2+)-induced H+ efflux. We also observed that the Ca2+/H+ antiport activity depends, essentially, on the DeltapH component of the electrochemical gradient (approximately 3 nmol Ca2+ taken up/mg protein), although the Deltaphi component may also support some Ca2+ accumulation by the vesicles (approximately 1 nmol/mg protein) in the absence of DeltapH. Both Ca(2+)-induced H+ release and DeltapH-dependent Ca2+ uptake could be driven by an artificially imposed proton motive force. Under normal conditions (H+ pump-induced DeltapH), the electrochemical gradient dependence of Ca2+ uptake by the vesicles was checked by inhibition of the process with specific inhibitors (bafilomycin A(1), ergocryptin, folymicin, DCCD) of the H(+)-pump activity. These results indicate that synaptic vesicles Ca2+/H+ antiport is indirectly linked to ATP hydrolysis and it is essentially dependent on the chemical component (DeltapH) of the electrochemical gradient generated by the H(+)-pump activity. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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