P2869Role of PDE8 in cAMP dynamics in human atrial fibrillation

Abstract

Abstract Background Cardiac arrhythmias, such as atrial fibrillation (AF), are often related to remodeling of membrane receptors and alterations in cAMP-dependent regulation of Ca2+ handling mechanisms. For instance, decreased L-type calcium current (ICa,L) density but upregulated RyR2 are major hallmarks of AF. These inhomogeneous AF-associated changes of protein phosphorylation point to a local regulation of PKA activity within these intracellular compartments. Local cAMP compartmentation and the role of phosphodiesterase (PDEs) have ben extensively studied in ventricular myocytes from animals. However, only a few studies have evaluated the contribution of PDEs to the pathophysiology of AF and the reason for the persistent AF-associated hypophosphorylation of the L-type calcium channel (LTCC) is currently unknown. The aim of this study was to investigate whether a change in the expression level of PDE8 in human atrium may affects cAMP nearby LTCC promoting the reduction of the ICa,L observed in persistent AF. Methods Atrial myocytes were isolated from tissue of 47 patients in sinus rhythm (SR) and with AF. Cells were then transfect with an adenovirus (Epac1-camps or pm-Epac1-camps) in order to express the (cytosolic or membrane, respectively) FRET-based cAMP sensor and cultured during 48 hours. Föster-resonance energy transfer (FRET) was used to measure cAMP in 232 isolated human atrial myocytes. Ro-20-1724 (10 μM), Cilostamide (1 μM) and PF-04957325 (30 nM) and IBMX (100 μM) were used as PDE4, PDE3, PDE8 and non-selective phosphodiesterases (PDEs) inhibitor respectively. Results Effects of PDE4 and especially PDE3 inhibition on cytosolic [cAMP] are reduced in AF. Pharmacological PDE8 inhibition induces only a small increase in basal intracellular [cAMP] in AF but it showed a big synergic effect when PDE4 was inhibit at the same time. By contrast, PDE8 inhibition dramatically increased basal [cAMP] in the subsarcolemmal compartment in AF while PDE3 or PDE4 inhibition had a smaller effect that didn't change between SR and AF. Conclusions PDE8 controls basal cytosolic cAMP levels in human atrial myocytes from patients with persistent AF while PDE3 effects tends to be reduced in these patients. Furthermore, PDE8 is the main PDE in controlling cAMP levels at the membrane in persistent AF. Thus, our study may provide a clue for the reported reduction of the ICa,L in persistent AF.