The effects of PDE3 and PDE4 inhibition on cAMP dynamics upon activation of β₁-adrenergic receptors.

<p><b>Panel A:</b> Simulated time courses of cellular cAMP concentrations for control conditions (solid line), upon inhibition of PDE3 (dashed line), and upon inhibition of PDE4 (dotted line) after sustained application of 0.1 µM isoproterenol at time moment <i>t</i> = 0 s. Activities of PDE3 or PDE4 are inhibited by 90% to simulate the effects of corresponding selective inhibitors, cilostamide or milrione for PDE3, or rolipam or Ro 20–1724 for PDE4. <b>Panel B:</b> Simulated time courses of cellular cAMP concentrations for control conditions (solid line), upon inhibition of PDE3 (dashed line), and upon inhibition of PDE4 (dotted line) after pulsed application of 0.1 µM isoproterenol at time moment <i>t</i> = 200 s for 30 s (thick solid line). The degrees of inhibition of PDE3 and PDE4 are the same as in Panel A.