Collapse of ATP-Induced pH Gradient by Sodium Ions in Microsomal Membrane Vesicles Prepared from Atriplex gmelini Leaves

Abstract
Sealed microsomal membrane vesicles were prepared from leaves of a 250 millimolar NaCl-grown halophyte (Atriplex gmelini C.A. Mey). The vesicles exhibited ATP-dependent proton-transporting activity which was inhibited 60% by NO3- (50 millimolar) but not by vanadate (100 micromolar) and 23% by oligomycin (10 micrograms per milliliter), suggesting that tonoplast-derived vesicles were the major constituents of the preparation. The pH gradient established by the vesicles by ATP in the presence of oligomycin collapsed upon the addition of Na+ salts. The vesicles took up Na+ ions in the presence of ATP and this activity was canceled by gramicidin. These results suggest that Na+ ions were taken up by the vesicles via a Na+-specific uptake system, possibly a Na+/H+ antiport.