Potassium and Rubidium Effluxes in Saccharomyces cerevisiae

M aría D . O rtega and A lonso Rodrí guez-N avarro Departamento de Microbiologfa, Escuela Tecnica Superior de Ingenieros Agrönomos, 14071 Cordoba, Spain Z. Naturforsch. 40c, 721 — 725 (1985); received May 22, 1985 Saccharomyces cerevisiae, Potassium Efflux, Rubidium Efflux, Potassium Transport, K+/K+ Exchange In growing cells, K+ and Rb+ effluxes followed first order kinetics, took place with slight differences between K+ and Rb+ and were stimulated at acidic pH values. In uncoupled cells and ATP-depleted cells, K+ efflux was higher than Rb+ efflux. In ATP-depleted cells, the effluxes were not stimulated at acidic pH values. Two different K+ effluxes are proposed: (i) the normal efflux, which may be a K+/H + antiport and does not function in ATP-depleted cells, and (ii) the backward reaction of the uptake system, which can be high in depolarized cells. The role of the normal efflux system in K+ content and pH regulation is discussed.