Simultaneous determination of potassium and rubidium content in yeast

Rubidium is widely used as a potassium analogue in transport studies in yeast and other organisms. As rubidium (potassium) uptake is modulated by the internal potassium concentration, it is often necessary to determine both Rb(+) and K(+) concentrations in the same cell extract. Current methods based on atomic absorption/emission spectroscopy require separate analysis for each cation. Alternatively, unsafe radioactive isotopes can be used. Here we report a convenient, non-radioactive, HPLC/conductivity-based method that allows a complete analysis of both cations with a single injection from a cell extract. The increase in Rb(+) uptake during K(+) starvation in yeast is easily demonstrated with this method.