Changes of the V_1/2 of the P_o^c-V curves of various mutants in response to 3 mM ATP at pH_i 6.8. The P_o^c-V curves of each mutant in the absence and in the presence of 3 mM ATP were constructed from the same patch, and the V_1/2 of the P_o^c-V curves were obtained by fitting the data points to a Boltzmann equation. The difference in V_1/2 between control and 3 mM ATP (ΔV_1/2) was first determined from each patch and then averaged (n = 14 for WT CLC-1 and n = 4–7 for various mutants). The label n.c. indicates that the mutant did not show functional current in at least two runs of expression in Xenopus oocytes. Error bars represent SEM.