Fig. 4. MrgC agonist potentiates acute inhibition of cAMP production by morphine.

(A) Dose-response curve of morphine to inhibit forskolin-induced cAMP production in HEK293T cells coexpressing MOR, MrgCII, and cAMP biosensor construct (n = 4 experiments). (B) Dose-response curve of BAM8–22 effect on forskolin-induced cAMP production (n = 3 experiments). (C) Time course of forskolin-induced cAMP production in response to different drug treatments in HEK293T cells (n = 6 to 8 experiments). (D) Quantification of forskolin-induced cAMP production after different drug treatments (n = 7 to 12 experiments). (E) Time course of effects of different drug treatments on superactivation of the cAMP pathway in HEK293T cells after withdrawal from 14-hour chronic morphine (10⁻⁶ M) or vehicle treatment (n = 25 to 27 experiments). (F) Quantification of different drug treatments on chronic morphine- induced cAMP superactivation in cells transfected with MOR alone and in cells cotransfected with MOR and MrgC11 (n = 25 to 29 experiments). (D and F) One-way ANOVA with Bonferroni post hoc test. *P < 0.05, **P < 0.01, and ***P < 0.001 versus control (blue bar); ##P < 0.01 versus the indicated group. All values are mean ± SEM.