Abstract 18233: Ca2+/Calmodulin-Dependent Protein Kinases II Phosphorylation of Ryanodine Receptor 2 Contributes to the Development of Chronic Atrial Fibrillation
Introduction: Cardiac ryanodine receptor (RyR2) mediated abnormal Ca2+ release has been implicated in the initiation and maintenance of atrial fibrillation (AF). We previously demonstrated that Ca2+/calmodulin-dependent protein kinases II (CaMKII) phosphorylation of RyR2 at S2814 is increased in patients with chronic AF and enhances sarcoplasmic reticulum (SR) Ca2+ leak associated with AF.
Hypothesis: CaMKII-mediated phosphorylation of S2814 on RyR2 contributes to the development of chronic AF.
Methods: CREM-IbΔC-X transgenic mice (CREM) were used as a mouse model for chronic AF. Ambulatory ECG recordings were performed to confirm the presence of chronic AF in CREM mice. Ca2+ spark frequency (CaSF), SR Ca2+ leak and SR Ca2+ load were measured in Fluo4-loaded atrial myocytes from WT and CREM mice. Expression of auto-phosphorylated CaMKII (CaMKII-pT287) and phosphorylated RyR2 (RyR2-pS2814) was detected in atrial tissue from WT and CREM mice.
Results: Telemetry ECG recordings confirmed that CREM transgenic mice exhibited chronic AF at 7-month of age. Atrial myocytes from CREM mice showed increased CaSF, which was decreased by CaMKII-inhibitor KN-93 (CREM: 43 mm−1s−1 vs. WT: 19 mm−1s−1 P <0.05, CREM+KN-93: 14 mm−1s−1 P <0.05, n=8 each group). Augmented SR Ca2+ leak in CREM (CREM: 12.1±2.7%, n=9 vs. WT: 5.5±0.71%, n=15; P <0.01) resulted in a reduction of SR Ca2+ load (CREM: 1.67±0.17 a.u. vs. WT: 2.26±0.14 a.u; P <0.05). KN-93 normalized the SR Ca2+ leak (5.0±0.84%, n=11; P <0.05) and SR Ca2+ load (2.41±0.42 a.u.; P <0.01) in CREM mice . The levels of CaMKII-pT287 and RyR2-pS2814 phosphorylation were 70% and 120% higher in atrial tissue from CREM mice compared with WT mice (P <0.05, n=6, 8, respectively). Expression levels of phosphotase 2A were decreased by 26% (P <0.05, n=4) whereas phosphatase 1 expression was not altered in CREM mice compared with WT mice. There are no changes in expression of SERCA, calsequestrin and Na+/Ca2+ exchanger in CREM mice.
Conclusions: These data suggests that overactivation of CaMKII increases phosphorylation of RyR2 and enhances SR Ca2+ leak, which may contribute to the maintenance of chronic AF in CREM transgenic mice. Inhibition of CaMKII phosphorylation of S2814 on RyR2 might be a potential target for AF treatment.
- © 2010 by American Heart Association, Inc.