FIGURE 4.

cAMP levels in PDE4B- and PDE4D-null MEFs stimulated with 100 nm PGE₂. A, cells were incubated for the indicated times with 100 nm PGE₂, and cAMP concentration in the cell extracts was measured by RIA. The graph reports the mean ± S.E. of three separate experiments. B and C, MEFs transduced with cytEpac2 (B) or pmEpac2 (C) were incubated for the indicated times with 100 nm PGE₂, and the percent change in FRET (%ΔF) was calculated. In each case, the cell number (n) is given. D, the cAMP response to 100 nm PGE₂ treatment for MEFs expressing either cytEpac2 or pmEpac2 expressed as the area under the curve (AUC). Data were analyzed using the unpaired t test; ***, p < 0.0001 (WT versus PDE4B^−/− and PDE4D^−/−; pmEpac2); *, p = 0.0113 (WT versus PDE4D^−/−; cytEpac2) and p = 0.604 (WT versus PDE4B^−/−; cytEpac2). Data represent mean ± S.E. Error bars, S.E.