FIGURE 8.

Effect of PKA on β₂-adrenergic cAMP signals is blunted in PDE4DKO MEFs. A and C, wild type (A) and PDE4DKO (C) MEFs were pretreated with the PKA inhibitor H89 (10 μm) or vehicle (DMSO) for 15 min. Cells were then stimulated with 10 μm ISO for the indicated times. Incubations were terminated by the addition of 0.1% trichloroacetic acid in 95% ethanol and intracellular cAMP was measured by RIA. Data shown represent means ± S.E. of three experiments. PKA inhibition with H89 has a greater effect on cAMP accumulation in wild type MEFs (**, p < 0.001; two-way ANOVA) compared with PDE4DKO cells (*, p < 0.05). B and D, wild type (B) and PDE4DKO (D) MEFs infected with an adenovirus encoding the protein kinase A inhibitor peptide (+PKI) or with green fluorescent protein as a control (–PKI) were stimulated for 3 min with 10 μm ISO. Incubations were then terminated, and intracellular cAMP was measured by RIA. Data shown represent means ± S.E. of three experiments. Statistical significance was determined using Student's t test. ***, p < 0.001; n.s., not significant.