FIGURE 9.

β₂AR desensitization is altered in the absence of PDE4D. A and B, wild type and PDE4DKO MEFs were stimulated with 10 μm ISO for the indicated times. A separate group of cells were incubated with ISO for 15 min and were then quickly washed four times with PBS and restimulated for the indicated times with 10 μm ISO. All incubations were terminated by the addition of 0.1% trichloroacetic acid in 95% ethanol, and cAMP concentrations were measured by RIA. Data reported are the means ± S.E. of three to six experiments. B, maximal cAMP accumulation during the second ISO stimulation is compared with that during the initial ISO stimulation. Statistical significance between cAMP accumulation in wild type and PDE4DKO MEFs was determined using Student's t test. *, p < 0.05.