Fig. 1.

Twenty-four-hour pretreatment with PGE₂ induces desensitization of cAMP responses to PGE₂ but not isoproterenol. HFL-1 cells were treated with vehicle or 100 nM PGE₂ for 24 h and washed, then acute responses to PGE₂ were measured using the cADDis cAMP sensor. Fluorescent decay curves are shown for three concentrations of PGE₂ in vehicle-pretreated (a) or PGE₂-pretreated (b) cells. The plateau from each decay curve was normalized to the maximal response to 200 mM IBMX plus 1 μM forskolin and plotted as a concentration-response curve. Concentration-response curves to PGE₂ (c) or isoproterenol (d) are shown in both vehicle and 100 nM PGE₂-pretreated cells. Data are mean ± SEM of n = 3–10. c Significant (p < 0.0001) and d not significant (p = 0.070) by 2-way ANOVA