Differential modulation of ΔR-CFTR gating by cytoplasmic and pipette NO₃⁻. (A) Cytoplasmic NO₃⁻ boosts the P_o of ΔR-CFTR when the pipette is filled with NO₃⁻-containing solution. (B) Single-channel kinetic analysis reveals: First, external NO₃⁻ has slight effects on gating parameters (∼12% increase of the P_o compared with Fig. 5 B). Second, in the presence of pipette NO₃⁻, similar gating modulations as described in Fig. 5 B were observed when cytoplasmic Cl⁻ was replaced with NO₃⁻, indicating that the major binding site for the gating effect of NO₃⁻ is located on the cytoplasmic side of the membrane. P_o, τ_o, and τ_c are as follows: 0.48 ± 0.02, 403 ± 49 ms, and 404 ± 57 ms for Cl⁻; and 0.71 ± 0.02, 776 ± 94 ms, and 281 ± 29 ms for NO₃⁻ (n = 15). The error bars represent the SEM of the mean.