Ion specificity of Na+-transporting systems in the plasma membrane of the halotolerant alga Tetraselmis (Platymonas) viridis

Vesicular preparations of plasma membranes (PM) from the microalga Tetrasel mis (Platymonas) viridis Pouch were used to investigate the ion specificity of the Na+/H+ antiporter and Na+-translocating ATPase, two Na+-transportin g systems previously identified functionally by our studies of T. viridis P M. The Na+/H+ antiporter and Na+-ATPase were shown to translocate, with sim ilar efficiencies, Nai. and Li+ across the membrane, whereas other cations, such as K+, Rb+, and Cs+, were not transported by these systems. Transport of the latter cations across PM of T. viridis occurred through the ion cha nnels of PM, which were apparently selective for K+.