Plasma membrane vesicles isolated from the halotolerant alga Dunaliella salina catalyze Na+/H+ antiport in a manner that is highly specific for Na+ (apparent K m ≅ 16 mM). Li+ and amiloride inhibit the process competitively with apparent K i values of 38 and 37 μM, respectively. It is suggested that Na+/H+ antiport in this organism plays a major role in maintaining low intracellular Na+ concentrations and may also function to drive Na+/HCO3 − symport, an important step in photosynthetic carbon fixation.
