[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-, NO3-, 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+ greater than Cs+ greater than Na+ greater than Li+. The H+-transport activity was inhibited by 0.3 mM ethacrynic acid, 10 microM 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 mM ouabain, 500 microM vanadate, 10 microM picrotoxin and 100 microM gamma-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.