Collapse of ATP-Induced pH Gradient by Sodium Ions in Microsomal Membrane Vesicles Prepared from Atriplex gmelini Leaves: Possibility of Na/H Antiport.

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 NO(3) (-) (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.