FIGURE 6.

Intrinsic cAMP signaling capacity is not affected in PDE4DKO MEFs. A, the basal intracellular cAMP concentration in wild type and PDE4DKO MEFs in all experiments performed is reported. The horizontal lines represent the average of at least 14 separate experiments. cAMP levels in wild type and PDE4DKO cells are not significantly different (p > 0.05; Student's t test). B, PDE4DKO and matched wild type MEFs were pretreated for 5 min with 10 μm rolipram. Cells were then stimulated with 10 μm ISO for the indicated times, after which the incubations were terminated and cAMP concentrations were determined by RIA. Treatment with rolipram elevates cAMP accumulation in both wild type and PDE4DKO MEFs (compare panel B with Fig. 4A). In the presence of rolipram, the genetic inactivation of PDE4D has no effect on ISO-induced cAMP accumulation compared with wild type controls (p > 0.05, two-way ANOVA).