FIGURE 1.

pH_i modulates CFTR Cl⁻ current. A, time courses of wild-type CFTR Cl⁻ current in excised inside-out membrane patches. In this and subsequent figures, unless otherwise indicated, ATP (0.3 mm) and PKA (75 nm) were continuously present in intracellular solutions, which were adjusted to the indicated pH_i; voltage was −50 mV, and there was a large Cl⁻ concentration gradient across the membrane ([Cl⁻]_int, 147 mm; [Cl⁻]_ext, 10 mm). For the purpose of illustration, time courses have been inverted, and upward deflections represent inward currents. B, effects of pH_i on CFTR Cl⁻ currents. Data are means ± S.E. (n = 6) expressed as a percentage of the control current at pH_i 7.3. The asterisks indicate values that are significantly different from the control (p < 0.05). C, relationship between intracellular proton concentration ([H_i⁺]) and CFTR activity. Data from B are plotted versus [H_i⁺]. The continuous line is the fit of a hyperbolic function to the mean data (y = y₀ + ax/(b + x), where y₀ = 70.9, a = 84.7, and b = 8.8 × 10⁻⁸; r = 0.99). Error bars are smaller than symbol size except where shown.