was longer when compared to that observed with morphine (cf. Figure 3A and Figure 3C). Figure 4E is a plot that compares the fentanyl concentration-response relationships for 118AA (●) and118GG (▲) neurons. The data points were also fitted to the Hill equation as described above (see Materials and Methods, pages 7 to 8, second paragraph). It can be seen that the curves for both group of neurons were nearly identical. The IC50 (nM), maximum current inhibition (%, ± s.e.m.) and Hill coefficient (± s.e.m.) for 118AA neurons were: 62, 52 ± 15.1 [4 to 100] and 0.55 ± 0.66 [-1.56 to 2.65] for 118AA neurons, respectively; while in 118GG neurons these values were: 102, 79 ± 89 [-204 to 363] and 0.31 ± 0.77 [-2.15 to 2.77]. The 95% confidence intervals are shown in brackets. Comparison of both curve fits did not show a significant difference (P = 0.63).
