(A–C) Effect of low extracellular K⁺ on the cells:medium ³⁶Cl⁻ ratio of cells grown in low Cl⁻ medium. Cells (sul1 in BY4741 background) were grown 16 h in LCAPG, 2% glucose, and ³⁶Cl⁻ (total of 8 μM Cl⁻). The medium initially contained either 1 mM K⁺ (normal APG) or 0.3 mM K⁺. After aerobic growth at 30°C for 16 h, cells were centrifuged, washed once in cold water, and the [K⁺] (B) and [³⁶Cl⁻] (C) distribution ratios were measured. The final extracellular K⁺ concentrations were 0.45 mM and 0.06 mM, respectively, for the media that had initially contained 1 mM and 0.3 mM K⁺. The total cellular K⁺ contents were the same in the two media (A). (D) Effect of low extracellular K⁺ on the cells:medium ³⁶Cl⁻ ratio of cells following a 2-h incubation. Cells (sul1) were grown 16 h in LCAPG medium containing 2 mM K⁺ and then incubated 2 h in fresh LCAPG medium containing 8 μM ³⁶Cl⁻ and either 0.1 mM or 1 mM K⁺. The media were buffered either at initial pH 4.5 with 5 mM Na-citrate or initial pH 7.6 with K-citrate, 10 mM bistris, 20 mM tris.