A, selective examples of single channel recordings of the CFTR mutants at 508 and 1068 positions are shown. The top level of each trace is the channel closed state. The values of the equilibrium constant, K, were calculated as ratios of the areas under the peaks on the all-points histogram (left) whereas the rate constants were calculated from the dwell-time histograms as ko= 1/τc and kc= 1/τo. The REFER plots for the processes of channel openings for CFTR mutants at position 508 (B) and 1068 (C) are shown. The type of amino acid is shown in one-letter code near each experimental point. Experimental points shown as mean values ±s.e.m. Slope Φ is shown under the graphs. The exact parameters of the best fit are: for the left graph slope is 0.953 ± 0.06 (R= 0.998, P < 0.0001), for the right line slope is 0.968 ± 0.05 (R= 0.989, P < 0.0001).