FIG 3.

Response of E. coli to valinomycin in various KCl concentrations. Fluorescence intensities of cells treated with valinomycin were normalized to fluorescence of valinomycin-treated cells in 0 KCl buffer (A) and to the corresponding buffers without valinomycin (1% DMSO only) (B). Error bars represent SEM. Three biological replicates were performed. (C) Assay dynamic range was determined by calculating the change in membrane potential upon valinomycin addition for each extracellular K⁺ concentration relative to 1 mM K⁺ (see Materials and Methods).