Abstract 2899: CaMKII Phosphorylation of RyR2 is Required for Atrial Fibrillation Induction in Mice
Background: Atrial fibrillation (AF), the most common human cardiac arrhythmia, is associated with abnormal intracellular calcium handling. Recently, we demonstrated increased Ca2+/calmodulin-dependent kinase (CaMKII) activity and CaMKII phosphorylation of S2814 on RyR2 in patients with chronic AF. Here, we tested the hypothesis that CaMKII phosphorylation of RyR2 is a critical downstream target of CaMKII involved in the induction of AF.
Methods and results: We generated knock-in mice in which serine 2814 on RyR2 was substituted by alanine (S2814A). RyR2-S2814A knock-in mice were born at rates consistent with a Mendelian inheritance pattern. In WT mouse heart, CaMKII was able to phosphorylate RyR2, and CaMKII inhibitor KN-93 prevented this phosphorylation event. CaMKII phosphorylation of RyR2 was inhibited in RyR2-S2814A homozygous knock-in mice, suggesting that S2814 is the major CaMKII phosphorylation site on RyR2. During baseline ECG recordings, none of RyR2-S2814A knock-in or WT mice developed spontaneous AF, and baseline heart rates were similar in both genotypes (WT: 564±12 bpm, RyR2-S2814A: 551±12 bpm). Because our previous studies suggested that AF can only be induced and maintained in the presence of a suitable substrate, we used a vagotonic AF model to determine the specific role of RyR2-S2814 phosphorylation for AF induction. In the presence of cholinergic stimulation with carbachol, rapid atrial pacing could induce AF in 44% of WT mice (7 of 16). In contrast, RyR2-S2814A knock-in mice were more resistant to pacing-induced AF in the presence of cholinergic stimulation with carbachol (7.7%, 1 of 13; P<0.05).
Conclusion: These findings suggest that in the presence of an arrhythmogenic substrate (i.e., cholinergic stimulation), rapid atrial pacing induced CaMKII phosphorylation of S2814 on RyR2 is the critical event supporting AF induction in mice.
This research has received full or partial funding support from the American Heart Association, National Center.