Evidence for a Na+/H+ Antiporter in Membrane Vesicles Isolated from Roots of the Halophyte Atriplex nummularia

摘要

The ATP-dependent establishment of a positive membrane potential (measured as S¹⁴CN⁻-accumulation) in membrane vesicles isolated from the roots of Atriplex nummularia Lindl. was not inhibited by NaMes and KMes at concentrations up to 140 millimolar. On the other hand, the formation of ΔpH (measured as ¹⁴C-methylamine accumulation or quenching of quinacrine fluorescence), was depressed by NaMes concentrations as low as 30 millimolar. Supply of NaMes after the ΔpH had been established brought about partial dissipation within 30 seconds. Extent of dissipation of ΔpH increased with NaMes concentration over the range tested (up to 180 millimolar). The H⁺/Na⁺ exchange indicated by these results was not due to the creation of a Na⁺ diffusion potential. Formation of ΔpH in these vesicles was stable to NO3⁻ up to 100 millimolar; further, the dissipating effect of Na⁺ supply was apparent on a ΔpH formed in the presence of 30 millimolar NO3⁻. Additional evidence that the origin of the membrane vesicles observed in this investigation was not the tonoplast and was probably the plasmalemma included the vanadate sensitivity of the establishment of the membrane potential.