Effect of the coexpression of K _V 7.3 on the deactivation kinetics at different pH _EXT . (A) K⁺ current recordings from oocytes expressing the WT K_V7.2 channel coexpressed with K_V7.3. The recordings were performed at pH_EXT 6.0 (left) and 8.0 (right). The holding potential was set to −90 mV, and the amplitude of the activating test pulses (V_ACT) ranged from −120 to +60 mV. Deactivation was driven at −105 mV. (B) Average I_ACT–V_ACT plots at pH_EXT ranging from 6.0 to 8.0. (C) K⁺-currents from oocytes coexpressing the mutant R198H with K_V7.3. In this case, the holding potential was set at −50 mV, which was close to the nominal Nernst potential of K⁺ in the experimental conditions. The test pulses ranged from −140 to +40 mV. Before the test pulses, the membrane potential was set to −120 mV. (D) Average I_TAIL–V_ACT for the mutant R198H coexpressed with K_V7.3. (E) K⁺ current recording from oocytes coexpressing the R198Q mutant along with K_V7.3 using the same protocol in C. (F) Average I_TAIL–V_ACT plots for the mutant R198Q coexpressed with K_V7.3. Solid lines in B, D, and F are the Fermi–Dirac function fitted to each average I_TAIL–V_ACT plot. (G) Average weighted V_1/2 for each of the WT and the mutants R198H and R198Q each coexpressed with the K_V7.3. The weighted V_1/2 was calculated from the parameters yielded from fitting a double Fermi–Dirac function to the I_TAIL–V_ACT from individual experiments. The solid lines correspond to a linear regression of the V_1/2 as a function of pH_EXT. We used a linear function to merely characterize the changes in V_1/2 not assuming any type of mechanism. (H) Average total apparent charge associated with gating. Statistical test performed using the WT as reference. T test confidence intervals are color coded. For WT: n = 5–9; for R198H: n = 8–12; for R198Q: n = 6–14.