FIGURE 4.

Knockdown of PDE4D9 and PDE4D8 affects the β₂AR-induced cAMP accumulation in cardiac myocytes. β₁AR-KO myocytes overexpressing mouse GFP-PDE4D isoforms together with the control (Con) or specific shRNAs for PDE4D9 or PDE4D8 are harvested. The protein levels of GFP-PDE4D are examined by imaging (A) and Western blot (B). In β₁AR-KO myocytes, ICUE3 is co-transfected with either PDE4D9 shRNA (C), PDE4D8 shRNA (D), or the control shRNA (E); and cells are stimulated with 10 μm isoproterenol. The time courses of changes in ICUE3 FRET ratio are measured and plotted. F, maximal increases in the FRET ratio induced by stimulation with 10 μm isoproterenol from C–E or after inhibition of PDE4 activities are plotted. #, p < 0.05 when compared with the control by two-way ANOVA. *, p < 0.05 and ***, p < 0.001 when compared with the control by Student's t test. ISO, isoproterenol; ROL, rolipram.