Cells were incubated with BK (10 μM) for 15 min followed by further incubation with the indicated concentrations of either U50488 (A) DPDPE (B), or 6’-GNTI (C) along with PGE2 (1 μM) for 15 min. Cellular cAMP levels were measured with radioimmunoassay. Data are expressed as the percentage of PGE2-stimulated cAMP levels and are the mean ± SEM of 4 separate experiments. When not visible, error bars are contained within the symbol. Concentration-response curves were analyzed with non-linear regression to determine EC50 and Emax values that are provided in the text. As shown in panel A, U50488-mediated inhibition of PGE2-stimulated cAMP levels was not altered in cells pretreated with the MEK inhibitor, U0126 (10 μM); F(1,42) = 1.764, P = 0.19.