Inactivation of WT-CFTR by CFTRinh-172. A continuous recording of WT-CFTR channels exposed to CFTRinh-172 during the closed state. Phosphorylated channels were first exposed to 5 µM CFTRinh-172 in the absence of ATP. In the continuous presence of the inhibitor, the application of 1 mM ATP elicited a biphasic current response with an apparent inactivation phase. In the same patch, when ATP was applied after the inhibitor was removed, a different biphasic current response appeared (see supplemental text for simulated results based on Scheme 3).