Abstract
Atrial fibrillation (AF)–associated remodeling includes contractile dysfunction whose reasons are only partially resolved. Serotonin (5-HT) increases contractile force and causes arrhythmias in atrial trabeculae from patients in sinus rhythm (SR). In persistent atrial fibrillation (peAF), the force responses to 5-HT are blunted and arrhythmic effects are abolished. Since force but not arrhythmic responses to 5-HT in peAF could be restored by PDE3 + PDE4 inhibition, we sought to perform real-time measurements of cAMP to understand whether peAF alters PDE3 + PDE4-mediated compartmentation of 5-HT4 receptor-cAMP responses. Isolated human atrial myocytes from patients in SR, with paroxysmal AF (paAF) or peAF, were adenovirally transduced to express the FRET-based cAMP sensor Epac1-camps. Forty-eight hours later, cAMP responses to 5-HT (100 μM) were measured in the absence or concomitant presence of the PDE3 inhibitor cilostamide (0.3 μM) and the PDE4 inhibitor rolipram (1 μM). We successfully established real-time cAMP imaging in AF myocytes. 5-HT increased cAMP in SR, paAF, and peAF, but in line with previous findings on contractility, this increase was considerably smaller in peAF than in SR or paAF. The maximal cAMP response to forskolin (10 μM) was preserved in all groups. The diminished cAMP response to 5-HT in peAF was recovered by preincubation with cilostamide + rolipram. We uncovered a significantly diminished cAMP response to 5-HT4 receptor stimulation which may explain the blunted 5-HT inotropic responses observed in peAF. Since both cAMP and force responses but not arrhythmic responses were recovered after concomitant inhibition of PDE3 + PDE4, they might be regulated in different subcellular microdomains.
Highlights
Atrial fibrillation (AF) is the most frequent arrhythmia but its treatment remains a challenge
To perform real-time cAMP measurements in human atrial myocytes (HAMs), we cultured isolated myocytes for 48 h and transduced them with an adenovirus to express the Förster resonance energy transfer (FRET)-based cAMP biosensor Epac1-camps (Fig. 1a) (Nikolaev and Lohse 2006). We previously used this protocol for sinus rhythm (SR) cells and a similar biosensor for cytosolic cAMP called Epac2-camps (Molina et al 2012), it has not been applied to AF cells so far
Basal FRET ratios were similar in all studied groups, paroxysmal AF (paAF) and specially persistent atrial fibrillation (peAF) myocytes showed a tendency towards increased basal FRET signal which might indicate a slightly higher basal cAMP levels in AF (Supplemental Fig. 1a)
Summary
Atrial fibrillation (AF) is the most frequent arrhythmia but its treatment remains a challenge. Conventional antiarrhythmic drugs have limited efficacy and increase the risk of ventricular arrhythmia (Nattel et al 1994; Dobrev and Nattel 2010). Modest progress with anti-AF drugs is mostly due to the fact that compounds were produced in the absence of specific. Naunyn-Schmiedeberg's Arch Pharmacol (2021) 394:291–298 molecular targets. Refinement of conventional ion channel blocker therapy as an atrial-selective approach has not yet led to an improvement. There is an urgent need to better understand the molecular pathophysiology of AF
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
