Die Rolle der PDE4 für Inotropie und elektrische Stabilität im menschlichen Vorhof

Abstract

Atrial fibrillation (AF) is a complex and multifactorial disease and the most common sustained cardiac arrhythmia in humans. Although the disease has been studied for many years, yet exhaustive treatments ensuring eradication of AF does not exist. According with the present literature, AF may be caused by two events: automaticity and/or re-entry. While re-entry is a macro phenomenon happening at the level of tissues connections, automaticity refers to the cellular mechanisms behind ectopic firing. In this thesis we focused indeed on the PKA/cAMP activation pathway and how it changes in cells and tissues isolated from patients in persistent AF (peAF) and paroxysmal AF (paAF). All the experiments were performed in human atrial trabeculae and myocytes isolated from patients in sinus rhythm (SR), paAF and peAF. L-type Ca2+ current (ICa,L) was measured in human atrial myocytes by patch clamp in whole-cell configuration; contractile force and arrhythmias were measured in human atrial trabeculae at 1 Hz each at 37°C; cAMP was recorded in human atrial cells by application of FRET (Fluorescence resonance energy transfer), after previous transfection of the cells with adenovirus encoding for Epac1-camps. In every experimental approach we apply G-proteins coupled receptors agonists norepinephrine (NE), epinephrine (Epi) and serotonin (5-HT) in the presence and in the absence of inhibitors of phosphodiesterases 3 and 4 (PDE3 and PDE4). PDE4B was higher expressed in peAF. However, selective inhibition of PDE4 by 10 M rolipram did not increase ICa,L neither in the absence nor in the presence of submaximum concentrations of NE or Epi in both SR and peAF. Furthermore, PDE4 inhibition did not shift the concentration response curve (CRC) for the positive inotropic effect of catecholamines to the left in SR as well as paAF and peaF. However, inhibition of PDE4 increased arrhythmias in SR and paAF but not in peAF. In peAF, increases in cAMP by β1- and by β2-AR stimulation are as high as in SR while increases after application of 5-HT are significantly smaller in peAF. Pre-treatment with PDE3 and PDE4 inhibitors succeeded to increase further cAMP levels in the presence of NE and Epi and restore the diminished response to 5-HT to same levels of catecholamines in peAF. In contrast, cAMP increases by inhibition of PDE3 and PDE4 alone were not different between SR and AF. The arrhythmia induction by rolipram in SR and paAF was not accompanied by an increase in ICa and force. The rescue of 5-HT inotropy in peAF by inhibition of PDE3 and PDE4 was not accompanied by an increase in ICa and arrhythmias. These findings suggest that cAMP is differently regulated in hypothetical compartments relevant for ICa, inotropy and arrhythmias.