Fig. 1.

G_i/o-coupled receptors endogenously expressed in SH-SY5Y cells share a common pool of AC. A, short-term inhibition of 5 μM forskolin-stimulated AC by 1 μM concentration of the indicated agonist alone. Agonist (receptor): DAMGO (MOR), SNC80 (DOR), OFQ (NOPr), UK14,304 (α₂AR), clonidine (α₂AR), CP 55,940 (CB₁), and 8-OH-DPAT (5-HT_1A). ***, p < 0.001 compared with DAMGO by one-way ANOVA with Bonferroni's post-test. B, coincubation with 1 μM DAMGO occludes inhibition by 1 μM concentration of all indicated agonists. All bars are not statistically different from 1 μM DAMGO alone (p > 0.05 by one-way ANOVA with Bonferroni's post-test). C, lower efficacy agonists (1 μM) were also not additive when coadministered in the indicated pairs (p > 0.05 for all pairs compared with the most efficacious agonist of the pair by one-way ANOVA with Bonferroni's post test). Data are presented as mean ± S.E.M. (n = 4, in duplicate) of the percentage of cAMP inhibition, where stimulation by 5 μM forskolin alone is represented as 0%.