Figure 1.

H⁺ enhances Slo1 currents in the absence of divalent cations in a His365- and His394-dependent manner. A. Representative macroscopic currents recorded at pH_i = 7.5 (left) and pH_i = 6.2 (right) without Ca²⁺. B. Voltage dependence of the fractional increase in the peak outward current size by pH_i = 6.2. Current sizes recorded at pH_i = 6.2 without Ca²⁺ were divided by those at pH_i = 7.5 without Ca²⁺. C. Macroscopic GV curves at pH_i = 7.5 (open circles) and pH_i = 6.2 (filled circles) without Ca²⁺. The V_0.5 values for the two conditions were 161.1 ± 2.6 mV (8) and 102.6 ± 3.8 mV (8). The Q_app values were 1.22 ± 0.041 e₀ (8) and 1.33 ± 0.055 e₀ (8). D. The double mutants H365R:H394R and H365A:H394A are largely insensitive to changes in pH_i. GV curves with pH_i = 7.5 (open circles) and 6.2 (filled circles) in H365R:H394R (left) and in H365A:H394A (right). n=6 and 9 for the H365R:H394R and H365A:H394A, respectively. The V_0.5 values for the pH_i =7.5 and 6.2 data for the H365R:H394R channel were 109.6 ± 4.9 mV and 102.1 ± 3.3 mV and the Q_app values were 1.31 ± 0.07 e₀ and 1.30 ± 0.05 e₀. The respective values for the H365A:H394A channel were 177.7 ± 1.4 mV and 171.3 ± 1.7 mV, and 1.31 ± 0.03 e₀ and 1.30 ± 0.04 e₀. n = 6 and 9 for H365R:H394R and H365A:H394A, respectively.