Voltage-independent stimulation of CFTR open probability by both 3NB and 3PP. (A and E) Macroscopic WT CFTR currents in 2 mM ATP (gray bars) at −80 (left traces) and 60 mV (right traces) and brief exposures to 32 mM 3NB (A, blue bars) or 20 mM 3PP (E, red bars). (B) Responses of macroscopic WT CFTR currents, elicited at −80 mV by repeated exposures to 2 mM ATP (gray bars), to applications of increasing concentrations of 3NB (blue bars). (F) Macroscopic WT CFTR currents elicited at −80 mV by exposures to 2 mM ATP (gray bars) either in the absence or in the presence (red bars) of various concentrations of 3PP. (C and G) Dose dependence of fractional currents on 3NB (C) and 3PP (G) concentrations at −80 mV (closed symbols) and Hill fits (solid lines; midpoints printed in the panels); open symbols and dotted lines show dose dependence of pore block, replotted from Fig. 3 (C and H). (D and H) Gating stimulation by 3NB (D) and 3PP (H) at −80 mV; P_o/P_o;control was calculated as the ratio (I/I_control)/(i/i_control). Control P_o (dotted lines), estimated for single WT channels under identical conditions (see Fig. 7 C), is ∼0.2. Mean ± SEM is shown.