Influence of cations on the membrane potential of Chlorella fusca

The influence of the chlorides of K, Na, Ca, Zn, Cd, Pb, and Ce on the membrane potential of Chlorella fusca (Shihira et Krauss) 211-8b, Göttingen, has been studied. The potential depended on the concentration of Na und K much less than predicted by the Goldman equation. The dependence on the concentrations of Ca, Zn, and Cd was qualitatively similar to that in the case of the alkali ions. With Pb and Ce, the potential was entirely suppressed already at moderate concentrations, i.e., in the millimolar range. The contrast between the effects of the inessential elements Cd and Pb on the potential corresponds to the difference between their paths of uptake. The dependence of the membrane potential on time has also been studied. With K, Na, and Ca stationary states were reached within about 1 hour. The time course of the depression of the potential by Pb depended on the concentration. At moderate concentration, suppression could be partly reversed by subsequent treatment of the cells with diluted KCl.