Role of PDE3 and PDE4 for β-adrenergic control of cAMP and ICa,L in adult rat ventricular myocytes

Abstract

β-Adrenergic stimulation increases cAMP in cardiac cells to induce PKA-mediated phosphorylation of various proteins regulating heart function, such as the L-type Ca 2+ channels which carry I Ca,L and trigger cardiac contraction. Phosphodiesterases (PDEs) 3 and 4 are the main cAMP degrading enzymes in cardiomyocytes and modulate the β-adrenergic regulation of I Ca,L but the significance of this dual regulation remains elusive. Here, we compared the participation of PDE3 and PDE4 in the β-adrenergic regulation of intracellular cAMP and I Ca,L using the FRET-based indicator Epac2-cAMPS and the whole-cell patch-clamp technique in adult rat ventricular myocytes. Isoprenaline (Iso, 100 nM, 15 s) induced a transient increase in both [cAMP] i and I Ca,L. PDE3 inhibition with cilostamide (1 μM) neither modified [cAMP] i nor I Ca,L transients, whereas PDE4 inhibition with Ro-201724 (10 μM) prolonged both signals. When both PDE3 and PDE4 were blocked, [cAMP] i and I Ca,L signals became nearly stable. PKA inhibition with PKI prolonged the β-adrenergic cAMP transient and this effect was not additive with that of Ro201724. Thus, PDE4 is predominant to terminate β-adrenergic induced [cAMP] i increase and I Ca,L stimulation in adult rat cardiomyocytes.