Prevention of adenosine A2A receptor activation diminishes beat-to-beat alternation in human atrial myocytes

Abstract

Atrial fibrillation (AF) has been associated with increased spontaneous calcium release from the sarcoplasmic reticulum and linked to increased adenosine A2A receptor (A2AR) expression and activation. Here we tested whether this may favor atrial arrhythmogenesis by promoting beat-to-beat alternation and irregularity. Patch-clamp and confocal calcium imaging was used to measure the beat-to-beat response of the calcium current and transient in human atrial myocytes. Responses were classified as uniform, alternating or irregular and stimulation of Gs-protein coupled receptors decreased the frequency where a uniform response could be maintained from 1.0 ± 0.1 to 0.6 ± 0.1 Hz; p < 0.01 for beta-adrenergic receptors and from 1.4 ± 0.1 to 0.5 ± 0.1 Hz; p < 0.05 for A2ARs. The latter was linked to increased spontaneous calcium release and after-depolarizations. Moreover, A2AR activation increased the fraction of non-uniformly responding cells in HL-1 myocyte cultures from 19 ± 3 to 51 ± 9 %; p < 0.02, and electrical mapping in perfused porcine atria revealed that adenosine induced electrical alternans at longer cycle lengths, doubled the fraction of electrodes showing alternation, and increased the amplitude of alternations. Importantly, protein kinase A inhibition increased the highest frequency where uniform responses could be maintained from 0.84 ± 0.12 to 1.86 ± 0.11 Hz; p < 0.001 and prevention of A2AR-activation with exogenous adenosine deaminase selectively increased the threshold from 0.8 ± 0.1 to 1.2 ± 0.1 Hz; p = 0.001 in myocytes from patients with AF. In conclusion, A2AR-activation promotes beat-to-beat irregularities in the calcium transient in human atrial myocytes, and prevention of A2AR activation may be a novel means to maintain uniform beat-to-beat responses at higher beating frequencies in patients with atrial fibrillation.

Mechanisms of arrhythmogenesis related to calcium-driven alternans in a model of human atrial fibrillation

“…Our results suggest that similar mechanisms may be at play in human AF as well, since increased propensity to CDA driven by RyR2 dysfunction led to increased arrhythmia vulnerability, complexity, and persistence in our model. Recent evidence for this comes from experiments in human atrial myocytes of control and AF patients, which identified a link between adenosine signaling, alternans, and calcium handling instability, potentially mediated by PKA regulation of RyR235. However, the mechanisms of RyR2 dysregulation in AF are extremely complex36 and controversial37.…”

Calcium Signaling and Cardiac Arrhythmias

“…264, 265 Atrial cardiomyocytes from patients with cAF are also more prone to Ca 2+ -alternans, an effect which appears to involve an increased activation of adenosine A 2A receptors with subsequent enhancement of RyR2-mediated SR Ca 2+ leak. 266 Overall, computer modeling clearly suggests that elevated Ca 2+ -driven APD alternans leads to increased arrhythmia vulnerability, complexity, and persistence due to increased heterogeneity of repolarization in atria. 267 …”

Purinergic Signaling in the Cardiovascular System

“…Prevention of A 2A receptor activation may be a novel way to maintain uniform beat-to-beat responses at higher beating frequencies in patients with AF. 132 Adenosineguided pulmonary vein isolation has been recommended, after a randomized clinical trial, for the treatment of paroxysmal AF, 133 but this has been questioned in a more recent clinical trial. 134 The clinical significance of ATP-induced AF has been investigated.…”