FIGURE 3.

Isoproterenol-dependent activation of PDE4 in MEFs. A, quiescent wild type and PDE4DKO MEFs were treated with 10 μm ISO for the times indicated on the abscissa. Cells were then lysed, and PDE activity in the resulting detergent extracts was determined in the presence or absence of rolipram. The graph depicts the rolipram-sensitive PDE4 activity. Data represent the means ± S.E. of three experiments. B, detergent extracts prepared from wild type MEFs treated for 5 min with or without 10 μm ISO were subjected to immunoprecipitation using subtype-selective PDE4 or splice form-selective PDE4D antibodies. Shown is the PDE activity recovered in immunoprecipitates corrected for the amount of protein used as IP input. All data represent means ± S.E. of the three experiments performed. The statistical significance of ISO-induced PDE activation was determined using Student's t test. ***, p < 0.001; **, p < 0.01; n.s., not significant.