An Inwardly Rectifying Cation Current across the Plasma Membrane of the Green Alga Eremosphaera viridis

Ion currents across the plasma membrane of the unicellular greenalga Eremosphaera viridis were characterized with electrophysiologicalmethods, especially the two electrode voltage-clamp-technique.Under different conditions, at increased external Cl^–concentrations or after perfusion of different anion channelblockers (A9C (anthracen-9-carboxylic acid), NPPB ((5-nitro-2-3-phenylpropylamino)benzoic acid) and ZnCl₂), increased instantaneous negative currentswere observed. The negative currents were carried by cationfluxes into the cell. The transporter responsible had low selectivityamong potassium and sodium. Additionally also divalent cationswere transported. The cation influx was not affected by thepotassium channel inhibitors TEA (tetraethylammoniumsulfate),Ba²⁺ or Cs⁺ at concentrations of 1 mM, but was strongly reducedby 100 µM AlCl₃. Our results with E. viridis demonstrate,for the first time for an unicellular alga, the existence ofan inwardly rectifying cation current across the plasma membrane.Parallels and differences to inwardly rectifying cation currentsand channels described in plasma membranes of other plant cellsare discussed. (Received May 10, 1993; Accepted September 13, 1993)