Plasma‐membrane hyperpolarization diminishes the cation efflux via Nha1 antiporter and E na ATP ase under potassium‐limiting conditions

S accharomyces cerevisiae extrudes K + cations even when potassium is only present in scarce amounts in the environment. Lost potassium is taken up by the T rk1 and T rk2 uptake systems. If the T rk transporters are absent or nonfunctional, the efflux of potassium is significantly diminished. A series of experiments with strains lacking various combinations of potassium efflux and uptake systems revealed that all three potassium‐exporting systems the Nha1 antiporter, E na ATP ase and Tok1 channel contribute to potassium homeostasis and are active upon potassium limitation in wild‐type cells. In trk1 Δ trk2 Δ mutants, the potassium efflux via potassium exporters N ha1 and Ena1 is diminished and can be restored either by the expression of TRK1 or deletion of TOK1 . In both cases, the relative hyperpolarization of trk1 Δ trk2 Δ cells is decreased. Thus, it is the plasma‐membrane potential which serves as the common mechanism regulating the activity of K + exporting systems. There is a continuous uptake and efflux of potassium in yeast cells to regulate their membrane potential and thereby other physiological parameters, and the cells are able to quickly and efficiently compensate for a malfunction of potassium transport in one direction by diminishing the transport in the other direction.