THE REVERSIBLE REPLACEMENT OF POTASSIUM BY RUBIDIUM IN ULVA LACTUCA

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Abstract
A review of the litera-ture on the substitution of rubidium for potassium reveals the extent of replacement or the suitability of rubidium for potassium physiologically. Study of the kinetics of the reversible exchange was carried'' out on the marine alga Ulva lactuca, measuring the cellular electrolytes. When placed in rubidium-sea water, rubidium replaces 2/3 of the potassium within 4 hours and 87% after 96 hours. On return of the alga to running sea water potassium re-accumulation is slower than the initial exchange. After 120 hours the potassium content nearly reaches that of the control, whereas the rubidium content is reduced to only 30% of its maximum value. Although disparity in the kinetics is evident, the assumption is that rubidium is transported into the cell by the same mechanism as is potassium.