The patch containing three phosphorylated WT-CFTR channels was deprived of ATP for 10 seconds or 180 seconds. Notice that after 10 seconds of ATP washout, the activity was restored almost immediately upon re-application of ATP (sweep II). In the following 5 minutes (from II to III), all three channel opening steps could be readily discerned. In contrast, after a 180-second long washout, only one opening step was seen upon addition of ATP (sweep IV), followed by an incremental recovery of activity to eventual all three opening steps (sweep V). The five expanded sweeps were extracted from the top trace at the marked time points. Each sweep is 20-second long. Dashed lines mark the zero-current level where all channels are closed. Similar observations were made in 3 patches.