Fig. 8. Voltage dependence of fentanyl block of inactivation-deficient hERG channels. S631A, S620T, and WT with ICA currents recorded using the voltage protocol shown above in the absence (CTL) or presence of 3, 30, or 2 µM fentanyl, respectively. The normalized current-voltage relationships in CTL and with fentanyl are shown in the middle. The currents measured after 100 milliseconds of the test voltages between −50 and 70 mV in CTL and with fentanyl were normalized to the maximal currents in CTL for each cell, and were plotted against the test voltages. Summarized ratios of currents with fentanyl vs. currents in CTL plotted against test voltages are shown at the bottom. S631A, n = 5; S620T, n = 8; WT with ICA, n = 5. Error bars represent the S.D. FENT, fentanyl; IS631A-Rel, relative hERG S631A current; IS620T-Rel, relative hERG S620T current; IWT-ICA-Rel, relative WT hERG current in the presence of ICA; IFENT/ICTL, ratio of current with fentanyl versus current in control.