Abstract
There are three different sodium transport systems (Ena1-4p, Nha1p, Nhx1p) in Saccharomyces cerevisiae. The effect of their absence on cell tolerance to alkali-metal cations and on membrane potential was studied.
All three sodium transporters were found to participate in the maintenance of cell Na+, Li+, K+ and Cs+ homeostasis. Measurements of the distribution of a fluorescence potentiometric probe (diS-C3(3) assay) in cell suspensions showed that the lack of all three transporters depolarises the plasma membrane.
The overexpression of the Na+,K+/H+ antiporter Nha1 resulted in the hyperpolarisation of the plasma membrane and consequently increased cell sensitivity to Cs+, Tl+ and hygromycin B. This is the first evidence that the activity of a Na+,K+/H+ antiporter could play a role in the homeostatic regulation of plasma membrane potential in yeast cells.