Abstract 3863: Does Hyperphosphorylation of the Cardiac Ryanodine Receptor at Serine 2808 Play a Role in the Progression of Cardiac Dysfunction After Myocardial Infarction?
Cardiac ryanodine receptor (RyR2) has been linked to cardiac arrhythmias and heart failure. It has been proposed that protein kinase A (PKA) hyperphosphorylation of the RyR2 at a single residue, Ser-2808 is a critical mediator of progressive cardiac dysfunction after myocardial infarction (MI). In present study, genetically modified mice in which Ser2808 was replaced by alanine (S2808A) to prevent phosphorylation were used to determine whether loss of functional PKA phosphorylation at Ser2808 can protect against cardiac dysfunction progression after MI.
Methods: MI was produced by permanent ligation of the left anterior descending coronary artery. In-vivo cardiac function was measured with the Visual Sonics Velvo 770 system. Myocytes were isolated and the effects of Isoproterenol (ISO) on LTCC Current (ICa-L), fractional shortening (FS) and Ca2+ transients were measured in wild-type (WT) and S2808A hearts 4 weeks after MI.
Results: Baseline cardiac function was similar in WT and RyR-S2808A mice. Ejection fraction (EF) and fractional shortening (FS) in WT mice are 58.1% and 29.1%, and 61.6% and 32.9% in RyR-S2808A mice. One week after MI, EF and FS were dramatically decreased in all animals (WT: 32.9% and 15.7%; RyR-S2808A: 26.9% and 12.1%), but there was no significant alterations in RyR-S2808A mice. 4 weeks after MI, there was still no significant difference between WT and RyR-S2808A mice in EF and FS (WT: 25.7% and 11.9%; RyR-S2808A: 27.1% and 12.8%). ICa-L after 4 weeks MI in WT and RyR-S2808A myocytes was not significantly different (−9.00±1.0 pA/pF, n=13; and −11.8±2.11 pA/pF, n=11). There were significant ISO responses in all myocytes, and no appreciable differences in responsiveness were found (WT vs. RyR-S2808A: −15.4±2.9pA/pF, n=13 vs. −16.3±2.7pA/pF, n=7). Contractions and Ca2+ transients were not significantly different in WT (FS: 9.4%±1.3; F/F0: 2.7±0.4) and RyR-S2808A myocytes (FS: 10.8±1.2%; F/F0: 2.7±0.1) after MI. Again, no difference was found in ISO responsiveness of RyR-S2808A myocytes.
Conclusions: Preventing PKA phosphorylation of RyR at Ser2808 has no effect on regulation of cardiac function under basal conditions and after MI. Preventing hyperphosphorylation of RyR at Ser2808 does not protect the heart or its myocytes.
This research has received full or partial funding support from the American Heart Association, Great Rivers Affiliate (Delaware, Kentucky, Ohio, Pennsylvania & West Virginia).