R352C shorten the locked-open time of hydrolytic-deficient CFTR mutant. Macroscopic current traces of E1371S-CFTR (A), R352C/E1371S-CFTR (B), T1246N/E1371S-CFTR (C), and R352C/T1246N/E1371S-CFTR (D). In each panel, the current was activated by PKA + ATP to a steady state, and then PKA and ATP were removed to allow the current to decay. The current relaxation was fitted with a single-exponential function resulting in the relaxation time constant for each mutant: 65.6 ± 10.1 s (n = 8) for E1371S-CFTR, 4.9 ± 0.8 s (n = 12) for R352C/E1371S-CFTR, 7.8 ± 1.6 s (n = 7) for T1246N/E1371S-CFTR, and 2.27 ± 0.27 s (n = 6) for R352C/T1246N/E1371S-CFTR. (E) Bar chart summarizing the results in A–D. *, P < 0.05 compared with E1371S; #, P < 0.05 between two designated data.