We measured temporal oscillations of intracellular K+ concentration in yeast cells exhibiting glycolytic oscillations using fluorescence spectroscopy and microscopy methods. These oscillations showed the same period as those of glycolytic metabolites (NADH, ATP), indicating a strong coupling between them. We experimentally ruled out that oscillations originate in extra- or intracellular K+ fluxes and conclude that these oscillations arise from fluctuations in free and adsorbed states of K+ in the cell interior. Oscillations in K+ showed a strong dependence on ATP and the organization of the cell cytoskeleton. Our results challenge the widely held view that intracellular K+ predominantly exists in a free state. They can, however, be productively understood in terms of Gilbert Ling's Association-Induction hypothesis.