A putative K(+)-selective channel in the plasma membrane of yeast that is blocked by micromolar concentrations of external divalent cations and is insensitive to tetraethylammonium.

At pH 7, addition of glucose to an anaerobic suspension of non-metabolizing yeast cells causes a transient net efflux of K+ from the cells and a concomitant transient hyperpolarization of the plasma membrane (Van de Mortel, J.B.J., et al. (1988) Biochem. Biophys. Acta 936, 421-428). Both phenomena are effectively suppressed in the presence of low concentrations of polyvalent cations. The concentrations of Mn2+, Ca2+, Ba2+, Mg2+, Sr2+ and La3+ required for half-maximal suppression of the transient hyperpolarization are 10, 17, 20, 38, 47 and 5 microM, respectively. Subsequent addition of EDTA 90 s after that of Ca2+ immediately restores both K+ efflux and cellular uptake of the fluorescent membrane potential probe 2-(dimethylaminostyryl)-1-ethylpyridinium (DMP). This suggests that an interaction of polyvalent cations with an external binding site blocks the putative K(+)-selective channel. Opening of this channel is not blocked by 20 mM tetraethylammonium nor by 100 microM 3,4-diaminopyridine. It is argued that this glucose-induced K(+)-conductive pathway is not identical to the voltage-gated K+ channels identified until now in patch-clamp studies of the yeast plasma membrane.