Normalized conductance increases during exposure to I ⁻ without affecting voltage dependence. (A) Normalized conductance (G_norm) plotted as a function of voltage for spHCN^R332C-expressing oocytes before (100K) and after exposure to 50 mM KI (100K+I) and labeled with ALEXA-488 (left) or MTS-TAMRA (right). Conductance was determined from tail currents in response to 1 s voltage steps using standard activation protocol (see Fig. 1 and Materials and methods). Data for individual cells were normalized to maximum conductance for the control (100K) condition, determined from a Boltzmann fit. Data points show mean ± SEM (n = 4) for each label. Fit parameters are given in Table S2. (B) Components of ΔF for ALEXA-488 labeling before (100K) and after exposure to I⁻ (100K+I) obtained by fitting ΔF–V data to a single exponential with variable offset (see text). Each component was normalized to $∆Ftotalmax$ for each cell and pooled. Continuous lines are fits using Boltzmann function to data. Fit parameters are given in Table S3.