CFTR recording in a giant patch demonstrating PKA activity. As a positive control for the patch-clamp experiments on α1β1FXYD1, we tested the ability of the same preparation of PKA to activate CFTR, typically a few days after the α1β1FXYD1 recordings. (A) Current recording at 0 mV from a large, inside-out patch excised from an oocyte 1 d after injection with human CFTR cRNA. Endogenous Na/K pumps were inhibited by incubating the oocyte in 10 µM ouabain before the experiment. The pipette contained the same external NMDG⁺ solution with 5 mM K⁺ as other patch clamp experiments, and the inside of the patch was perfused with 25 mM Na⁺ internal solution ([Na⁺] + [K⁺] = 140 mM). Under these experimental conditions (∼150 mM external Cl⁻ and ∼30 mM internal Cl⁻, 0 mV), CFTR currents are outward. Application of 4 mM ATP alone to the inside of the patch produced no change in the baseline current, but simultaneous application of ATP with 10 µM PKA catalytic subunit induced an outward current that returned to baseline upon their removal. The large, vertical current deflections before the initial PKA application are 25-ms I-V pulses. (B) Enlargement of the current trace enclosed by the dashed box in A. Single-channel openings are visible ∼10 s after application of ATP and PKA.