ERK/β-arrestin interaction signals in response to activation of endogenous GPCRs in U2OS cells. (A) Dose-response curves generated using the ERK/β-arrestin interaction assay in response to varying doses of GPCR agonists adrenaline, isoproterenol, dopamine, and S1P. Cells were stimulated with varying doses of GPCR agonists in serum-free DMEM for 90 min at 37°C. (B) Antagonists inhibit GPCR agonist-induced ERK/β-arrestin interaction signals. Cells were treated with varying doses of GPCR antagonists BD-1047, ICI118551, and Clozapine in serum-free DMEM for 15 min and then treated with 1 μM adrenaline, isoproterenol, and dopamine respectively for 90 min.