(A) The GTP turnover assay shows that GCGR activation of Gs is largely independent of GDP concentration, but upon pre-coupling of GCGR with RAMP2, Gs activation is potently inhibited in a [GDP] dependent manner and appears to inhibit even intrinsic Gs activity. (B) The rate of 3H-GDP release from Gs is significantly reduced when GCGR is pre-incubated with RAMP2. (C) Increasing the cell-surface expression of the glucagon receptor, but not β2AR, results in an increase in surface expression of RAMP2. (D) Cells transfected with GCGR display increases in cAMP levels upon stimulation with glucagon with an observed EC50 of 0.28 nM (pEC50=9.6 [95% confidence limits 9.8–9.3]); cells expressing the same levels of GCGR in the presence of excess transfected RAMP2 display an EC50 of 1.10 nM (pEC50=9.0 [95% confidence limits 9.1–8.8]), a 4-fold right-shift in potency.