The effects of ketoconazole and miconazole uptake on K+ transport and the internal pH of Saccharomyces cerevisiae were studied. The uptake of both drugs was very fast, linear with concentration and not dependent on glucose, indicating entrance by diffusion and concentrating inside. Low (5.0 mu M) to intermediate concentrations (40 mu M) of both drugs produced a glucose-dependent K+ efflux; higher ones also produced a small influx of protons, probably through a K+/H+ exchanger, resulting in a decrease of the internal pH of the cells and the efflux of material absorbing at 260 nm and phosphate. The cell membrane was not permeabilized. The K+ efflux with miconazole was dependent directly on the medium pH. This efflux results in an increased membrane potential, responsible for an increased Ca2+ uptake and other effects. These effects were not observed with two triazolic antifungals. A decrease of the Zeta (zeta) potential was observed at low concentrations of miconazole. Although the main effect of these antifungals is the inhibition of ergosterol synthesis, K+ efflux is an important additional effect to be considered in their therapeutic use. Under certain conditions, the use of single mutants of several transporters involved in the movements of K+ allowed to identify the participation of several antiporters in the efflux of the cation. (C) 2010 Elsevier B.V. All rights reserved.