TABLE 2.

E_max and EC₅₀ values of fixed-proportion agonist/antagonist mixtures in ligand-modulated [³⁵S]GTPγS binding

E_max, EC₅₀, and Hill coefficient values are derived from the concentration-effect curves shown in Fig. 3. Fixed-proportion concentration ratios are expressed as X:1 agonist/antagonist, which are fentanyl/naltrexone (F/N) in MOR-expressing cells and CP55,940/rimonabant (C/R) in CB₁R-expressing cells. E_max values are expressed as a percentage of the stimulation produced by a maximally effective concentration (%Max) of a full agonist at each receptor type (DAMGO for MOR and WIN55,212-2 for CB₁R). EC₅₀ values for agonist alone and all mixtures are expressed as log M agonist concentration along with conversion to [nanomolar] concentration, whereas EC₅₀ values listed for each antagonist alone represent the log M EC₅₀ [nanomolar] concentration of the antagonist. For mixtures, the antagonist concentration at the EC₅₀ value can be calculated as EC₅₀ ÷ fixed-proportion dose ratio of agonist to antagonist. All values are means ± S.E.M. (MOR n = 4; CB₁ n = 3–6). E_max or log EC₅₀ values without any overlapping letter designations (within each receptor type) are P < 0.05 different from each other by ANOVA with Tukey’s post hoc test.

Receptor	Mixture	Emax (%Max)	EC50 (log M)	Hill Coefficient
			nM
MOR	Fentanyl	100.1 ± 3.3a	−7.35 ± 0.01a [44.6]	1.00 ± 0.03
MOR	965 F:1 N	91.3 ± 0.8ab	−7.42 ± 0.05ab [39.4]	0.98 ± 0.03
MOR	322 F:1 N	85.5 ± 2.8b	−7.45 ± 0.02ab [35.5]	1.01 ± 0.03
MOR	107 F:1 N	71.7 ± 1.6c	−7.46 ± 0.03ab [35.4]	0.96 ± 0.06
MOR	35.8 F:1 N	38.7 ± 4.2d	−7.61 ± 0.07ab [25.6]	0.82 ± 0.06
MOR	11.9 F:1 N	25.8 ± 2.5de	−7.57 ± 0.04ab [27.6]	0.77 ± 0.11
MOR	3.97 F:1 N	15.0 ± 1.2ef	−7.72 ± 0.11b [21.9]	0.72 ± 0.05a
MOR	Naltrexone	5.2 ± 0.3f	−9.56 ± 0.10c [0.29]	0.83 ± 0.11
CB1R	CP55,940	93.3 ± 5.1a	−8.48 ± 0.05a [3.44]	0.99 ± 0.10
CB1R	128 C:1 R	97.0 ± 1.0a	−8.73 ± 0.11a [2.24]	1.00 ± 0.09
CB1R	42.7 C:1 R	90.9 ± 5.9a	−8.61 ± 0.17a [3.76]	0.88 ± 0.04
CB1R	14.2 C:1 R	62.6 ± 3.1b	−8.72 ± 0.11a [2.23]	0.96 ± 0.09
CB1R	4.75 C:1 R	33.2 ± 2.5c	−8.85 ± 0.17a [2.16]	1.11 ± 0.22
CB1R	1.59 C:1 R	8.1 ± 1.0d	−9.20 ± 0.36a [1.76]	0.69 ± 0.15
CB1R	0.526 C:1 R	−16.1 ± 3.4e	−10.3 ± 0.22b [0.09]	2.29 ± 0.49
CB1R	Rimonabant	−31.5 ± 2.2e	−9.20 ± 0.10a [0.72]	0.89 ± 0.11

^aa-e E_max or log EC₅₀ values without any overlapping letter designations (within each receptor type) are P < 0.05 different from each other by ANOVA with Tukey’s post hoc test. ^aHill coefficient is P < 0.05 different from one by Student’s t test.