Abstract 18551: Genetic Inhibition of Camkii-Phosphorylation of Ryr2 Prevents Atrial Fibrillation Induction
Introduction: Atrial fibrillation (AF), the most prevalent sustained cardiac arrhythmia, is associated with abnormal sarcoplasmic reticulum (SR) Ca2+ cycling. We have previously shown that mice lacking FKBP12.6 are more susceptible to pacing-induced AF due to abnormal SR Ca2+ leak. The purpose of this study was to determine whether pacing-induced activation of CaMKII increases the susceptibility to AF in FKBP12.6-/- mice.
Methods: RyR2-S2814A knockin mice, in which the CaMKII phosphorylation site on RyR2 was genetically inactivated, were intercrossed with FKBP12.6-/- mice. Programmed electrical stimulation was performed using an intracardiac catheter in FKBP12.6-/-, S2814A, and FKBP12.6-/-:S2814A crossed mice. AF was defined as the occurrence of rapid and fragmented atrial electrograms with irregular AV-nodal conduction and ventricular rhythm for at least 1 second. Calcium imaging was performed in single atrial myocytes loaded with Fluo-4/AM. RyR2 phosphorylation levels were also measured in all groups using Western blot.
Results: FKBP12.6-/-:S2814A mice exhibit a significantly lower incidence of pacing-induced AF (16%, 3 of 19) compared to FKBP12.6-/- mice (53%, 10 of 19; P<0.05). Atrial myocytes isolated from FKBP12.6-/-:S2814A mice exhibited fewer spontaneous calcium release events compared to FKBP12.6-/- mice (11% vs. 65% P<0.05). Moreover, FKBP12.6-/-:S2814A myocytes shows less SR Ca2+ leak (leak/SR Ca2+ load; 7.96±0.62% n=25) compared to FKBP12.6-/- (11.35±0.62% n=60; P<0.05). Finally, pacing induced an increased RyR2 phosphorylation at S2814 in FKBP12.6-/- mice but not FKBP12.6-/-:S2814A mice, as expected.
Conclusions: FKBP12.6 deficient mice were susceptible to AF only after rapid atrial pacing, which was associated with increased CaMKII phosphorylation of RyR2 at S2814. Genetic inhibition of RyR2 prevented the induction of pacing-induced AF in FKBP12.6-/- mice. Moreover, FKBP12.6:S2814A exhibited significantly fewer abnormal SR Ca2+ release events and reduced SR Ca2+ leak. Thus, CaMKII-mediated SR Ca2+ leak via RyR2 may play a critical role in the initiation of AF in mice.
- © 2010 by American Heart Association, Inc.