Figure 2.

Effect of extracellular pH on voltage activation of Kv12.1. (A) Kv12.1 current traces elicited by 4-s depolarization steps from −100 to 20 mV (in 20-mV increments from a holding potential of −100 mV) are shown for bath solutions of pH 6, 7, and 8. Tail step voltage was −40 mV. Recordings were made from a single Xenopus oocyte using TEVC. Scale bar: 2.5 µA, 1 s. (B) Normalized GV relations for Kv12.1 at pH 6 (black), 7 (red), and 8 (blue). Conductance values were taken from isochronal tail currents recorded at −40 mV after 4-s depolarization steps to the indicated voltages. Error bars show SEM (n = 3–8), and lines show single Boltzmann distribution fits. The gray line at −60 mV indicates the voltage used in Fig. 4 to examine pH-dependent changes in holding current for Kv12.1. (C) Plot of V₅₀ versus pH for Kv12.1. V₅₀ values were determined as in B, and the curve shows a three-parameter dose–response fit yielding a pK_a value of 6.5. Error bars show SEM (n = 3–8). (D) Current traces from the 20-mV voltage step in A are normalized and superimposed to highlight changes of activation time course; bath pH is encoded by color as in A. The graph shows the time necessary for Kv12.1 to reach 80% activation (t₈₀) during steps to 20 mV (from a holding potential of −100 mV) at pH 6, 7, and 8. A log₁₀ scale was applied to the t₈₀ axis to better visualize the entire range of values, and statistical significance was judged using a two-tailed nonequal variance Student’s t test. (E) Data are analyzed and presented as in D, but normalized for V₅₀ shift: the voltages selected for each pH were −30 mV for pH 8, −20 mV for pH 7, and 10 mV for pH 6 and corresponded as closely as possible to the same open probability, ∼V₉₈. Data in D and E are mean ± SEM (n = 8). (F) Comparison of Zn²⁺-dependent shifts in Kv12.1 GV relationships at pH 6 and 8; data (mean ± SEM; n = 3–5) are shown for controls (squares), 100 µM Zn²⁺, and 1 mM Zn²⁺, and curves show single Boltzmann distribution fits.