Figure 2.

Agonist-mediated accumulation of cAMP in cells individually expressing epitope-tagged δ, κ, and β₂ receptors or cells coexpressing δ-β₂ or κ-β₂ receptors. Cells were treated with indicated concentrations of etorphine (Left) or isoproterenol (Right) for 5 min at 37°C, and the intracellular cAMP level was measured by RIA as described under Materials and Methods. The amount of cAMP in cells without agonist treatment is taken as 100%. The data represent means ± SEM (n = 3–5).