Figure 5. The effects of β₁-adrenoceptor stimulation on PDE activities.

Panel A: Absolute total PDE activities and the activities of PDE2, PDE3, and PDE4 obtained experimentally from the mouse and rat hearts (in pmol/min/mg protein, bars with errors [44], [49]) and corresponding simulation data (bars without errors). Panel B: Fractional activities of PDE2, PDE3, and PDE4 obtained experimentally from the mouse and rat hearts (in %, bars with errors [44], [49]) and corresponding simulation data (bars without errors). Panel C: Partial activities of PDE2, PDE3, and PDE4 obtained experimentally from the particulate fraction of the rat hearts (in %, bars with errors [48]) and corresponding simulation data (bars without errors). In the experiments and simulations, PDE activities are obtained at fixed cAMP concentrations of 1 µM. Panel D: The effects of PDE inhibitor IBMX on cAMP levels in ventricular myocytes. Experimental data for rat [147] and canine [148] ventricular myocytes are shown by bars with errors, simulation data are shown by bars without errors. In the experiments with rat ventricular myocytes measurements were performed after 3-minute stimulations (5 µM isoproterenol, or 100 µM IBMX, or both) [147]. In the experiments with canine ventricular myocytes measurements were performed after 5-minute stimulations (10 µM isoproterenol, or 10 µM IBMX, or both) [148]. Simulated cAMP level is determined at the 3^rd minute upon application of 5 µM isoproterenol, or 100 µM IBMX, or both.