Is the Mg(2+)-ATP-dependent proton pumping activity of the synaptic vesicles a factor involved in the cerebral hypoxia?
The changes in the Mg(2+)-dependent V-type ATPase activity and the Mg(2+)-ATP-dependent H+ pumping activity of the synaptic vesicles from the cerebral cortex of rats submitted to intermittent chronic (4 weeks) mild or severe hypoxia were evaluated. The adaptation to the chronic severe hypoxia increases both the ATPase and the H+ pumping activities which are inhibited by NEM with an exponential relationship between the IC(50) values and the in vivo O2 concentration. The Mg(2+)-dependent increase in H+ pumping activity of synaptic vesicles from the rats subjected to in vivo chronic hypoxia may be antagonized by nigericin (dissipating delta pH) and by FCCP (dissipating delta pH and delta psi SV). In contrast, valinomycin (dissipating the delta psi SV) and facilitating an enhancement in delta pH) increases in vitro the H+ pumping activity that is inhibited by the addition of high concentration of K gluconate (reducing the rate of K+ efflux). The preincubation of vesicles from hypoxic rats with FCCP, but not with nigericin, inhibits the valinomycin-increased H+ pumping activity. L-glutamate increases the H+ pumping activity in synaptic vesicles from the cerebral cortex of chronic hypoxic rats, whereas other amino acids (i.e., L-aspartate and L-homocysteate) and glutamate analogs (i.e., quisqualate and ibotenate) are ineffective. The adaptation to both chronic intermittent severe hypoxia and in vivo treatment with posatireline causes a decrease in the Mg(2+)-ATPase activity consistent with the decrease in the H+ pumping one of the synaptic vesicles. The addition of nigericin into incubation medium magnifies the decrease in the H+ pumping activity, while the addition of FCCP is ineffective, suggesting that the treatment with posatireline interferes with the delta psi SV component in the delta mu H+ of the synaptic vesicles from rats submitted to chronic hypoxia. The results of the in vivo and in vitro experiments suggest that in the synaptic vesicles from hypoxic rats the delta psi SV component in delta mu H+ may be most effective in increasing the Mg(2+)-ATP-dependent H+ pumping activity.