Fig. 2. Characterization of CFTR-dependent GSH flux in the presence of MgAMP-PNP. (A) Time dependence of [³⁵S]GSH uptake by phosphorylated membrane vesicles either expressing wild-type CFTR protein (filled circles) or not expressing CFTR (open circles). All uptake reactions contained 65 µg of total protein and were carried out for 1, 5, 10, 30 or 60 min. GSH flux was normalized according to the amount of total protein in each treatment group. Flux values are expressed as the mean ± SEM (n = 2–4). (B) The osmotic sensitivity of [³⁵S]GSH uptake in the presence of MgAMP-PNP was determined by incubating CFTR-expressing vesicles in transport buffer containing various sucrose concentrations, ranging from zero to 750 mM. Values are expressed as the mean ± SEM (n = 2–4). Uptake values were normalized according to the amount of CFTR protein.