Voltage-independent inhibition of WT-CFTR by CFTRinh-172. (A) Continuous WT-CFTR current traces showing reversible inhibition by 1 or 10 µM CFTRinh-172. In an inside-out patch clamp experiment, after the channels in the patch were activated with 1 mM MgATP plus PKA, we applied 1 mM MgATP, followed by 1 mM MgATP plus 1 or 10 µM CFTRinh-172. The current recovery phase upon removal of 1 µM CFTRinh-172 was fitted with a single-exponential function, yielding a rate constant of 0.031 s⁻¹ (0.024 ± 0.003 s⁻¹; n = 17). (B) The concentration dependence of CFTR inhibition fitted with the Hill equation with IC50 = 1.16 ± 0.09 µM and Hill coefficient n = 1.31 ± 0.12. Each data point represents values determined from 6–14 patches. The error bars are smaller than the symbols. (Inset) The structure of CFTRinh-172. (C) Representative I-V curves in the presence (red) or absence (blue) of 1 µM CFTRinh-172. A voltage ramp over ±100 mV was applied to a patch yielding macroscopic currents. (D) Percent inhibition at different voltages was obtained from C. Data between −10 and 10 mV were discarded because of the small size of the signal. Similar observations were made in five patches. Inh-172 is the abbreviation for CFTRinh-172 in this and subsequent figures.