Sodium and Potassium Transport in the Marine Alga Chaetomorpha Darwinii

Ohaetomorpha darwinii is a marine alga with large coenocytic cells. The cell sap contains about 540 mM potassium, 25 mM sodium, and 600 mM chloride, and the vacuole is 10 mY positive to the sea water. The potassium selectivity is due to an active inward pump and an outward sodium pump at the plasmalemma. The fluxes of potassium at the plasmalemma and tonoplast were about 100 and 150 pmoles/cm2/sec, and the fluxes of sodium at these membranes were about 100 and 4 pmoles/cms/sec, respectively. The potential differences at these boundaries were -35 mY and +45 mY. The cytoplasmic phase contained about 18 p.-equiv/g of potassium and 0·5-1·0 p.-equiv /g of sodium.