Table 2.

Fentanyl‐ and DAMGO‐induced [³⁵S]‐GTPγS binding

	Parameter	MOR‐WT	MOR‐WT	MOR‐WT	MOR‐H2976.52A
		pH 7.4	pH 6.5	pH 6.0	pH 7.4
Fentanyl	EC50 (nM) [95% CI] log (EC50)	28.0 [12.9, 59.8] −7.55 ± 0.22	22.5 [4.9, 90.8] −7.65 ± 0.42	26.3 [9.1, 75.9] −7.58 ± 0.27	52.8 [8.9, 328.8] −7.28 ± 0.47
	E max (%)	178.1 ± 5.1	159.8 ± 7.2	169.6 ± 5.3	224.6 ± 19.9
DAMGO	EC50 (nM) [95% CI] log (EC50)	41.4 [20.7, 79.3] −7.38 ± 0.13	53.2 [23.2, 115.3] −7.27 ± 0.17	75.5 [27.4, 195.5] −7.12 ± 0.20	23 μM [5.7 μM, unknown] −4.63 ± 0.33*
	E max (%)	130.0 ± 1.2	116.7 ± 0.9*	116.2 ± 1.1*	114.3 ± 3.5*

Note. Data are means ± SEM or means with 95% confidence interval (95% CI); n = 6 per experiment. log (EC₅₀) values were compared by one‐way ANOVA with Dunnett's multiple comparison post hoc test, control group = MOR‐WT pH 7.4. E_max values were compared by one‐way ANOVA with Welch's correction for unequal SD, followed by Dunnett's T3 multiple comparison post hoc test. All comparisons were performed within agonist groups.

Abbreviations: E _max, maximum intrinsic activity; MOR‐WT, wild type μ‐opioid receptor; MOR‐H297^6.52A, μ‐opioid receptor mutated at H 297^6.52 to A.