Ca 2+-H + antiport activity in synaptic vesicles isolated from sheep brain cortex

Abstract

Synaptic vesicles isolated from sheep brain cortex exhibit an ATP-dependent Ca 2+ accumulation that is inhibited by the protonophore uncoupler carbonyl cyanide m-chorophenylhydrazone (CCCP) and completely released by the Ca 2+ ionophore ionomycin. This transport activity was sensitive to the V-type ATPase inhibitor, bafilomycin, but not to the P-type ATPase inhibitor, vanadate. We also observed that the proton gradient, established across the synaptic vesicle membranes in the presence of ATP, is partially dissipated by the addition of Ca 2+ (100–860 μM) in correlation to an increase of ATP hydrolysis by the H +-pumping ATPase. In contrast, the activity of the H +-ATPase, measured under uncoupling conditions (presence of CCCP), appears to be unaltered by the calcium ion. The Ca 2+-induced H + release visualized by fluorescence quenching of acridine orange correlates well with the Ca 2+ uptake determined isotopically. These results indicate that synaptic vesicles accumulate Ca 2+, via a low affinity Ca 2+–H + antiport system energized by the protonmotive force originated from the H +-pumping ATPase activity.