Potency and efficacy of potentiators for mutant CFTRs. (a) Representative traces of G551D-CFTR function assayed by halide-sensitive YFP quenching in CFBE cells treated with increasing concentrations of VX-770. The YFP quenching kinetics was determined in response to extracellular iodide addition in the presence of forskolin (10 μM), IBMX (250 μM), cpt-cAMP (250 μM), and indicated potentiator concentrations. (b) Dose-response of indicated potentiators for the R334W, R347H, S549N, S549R, G551D, G1244E potentiation measured by halide-sensitive YFP quenching assay in CFBE (n = 3−4). Values are expressed as percentage of the response to 3 μM VX-770 of the respective mutants. Data are means ± SEM of the indicated number of independent experiments.