Properties of ATP-dependent H+-transport in rat brain synaptosomes

Properties of the ATP-dependent H+-transport system in rat brain synaptosomes were examined using the acridine orange fluorescence quenching method. ATP-dependent H+-accumulation assessed by the quenching of acridine orange fluorescence was observed with the synaptosomes treated with hypotonic solution (hypotonic shock-synaptosomes), but not with the intact synaptosomes. With hypotonic shock-synaptosomes, H+-transport was activated in the presence of Cl- or Br-. However, this transport activity was markedly reduced in the presence of Mes-, N03-, I- or SCN-. On the other hand, H+-transport activity was less effective with cations other than K+ in the following decreasing order of potency: K+>Cs+>Na+>Li+. The H+-transport activity was inhibited by 0.3 mM ethacrynic acid, 10 μM 4-acetamide-4′-isothiocyanostilbene-2, 2′-disulfonic acid or 1 mM 4-aminopyridine to 39.2%, 36.3%, or 33.1%, of the control, respectively, but was not inhibited by 1 mMouabain, 500 μM vanadate, 10 μM picrotoxin and 100 μM γ-aminobutyric acid. These results suggest that the ATP binding site of the synaptosomal ATP-dependent H+-transport system exists on the internal surface of synaptosomal plasma membranes and that the H+-transport system is stimulated by the presence of Cl- or Br- and by K+ movement through the K+ channel.