Figure 4. Effect of EP₁ receptor activation on β₂ AR agonist–stimulated cAMP production, receptor sequestration and receptor phosphorylation.

(A) Pretreatment of ASM cells with 17-PTP (1 μM) for 15 minutes reduced isoproterenol-stimulated cAMP production. Data are mean ± SEM of 4 experiments. ^##P = 0.02 versus vehicle-treated cells. (B) Isoproterenol caused a time-dependent internalization of β₂AR in murine ASM cells over 30 minutes as assessed by whole-cell binding using the hydrophilic antagonist [³H]-CGP-12177; pretreatment with 17-PTP (1 μM for 15 min) had no effect on internalization. Data are mean ± SEM of 4 experiments. (C) EP₁ receptor activation failed to phosphorylate β₂AR or to alter isoproterenol-mediated β₂AR phosphorylation in HEK 293 cells transfected to express β₂AR and EP₁ receptors. Shown is a representative autoradiogram of 4 experiments. PMA, phorbol-12-myristate-13-acetate. NTF, nontransfected.