Abstract 881: Ablation of Serine 2808 Protein Kinase A Phosphorylation in the Cardiac Ryanodine Receptor Defines Novel Inotropic Mechanism in vivo
To evaluate the physiologic role of PKA phosphorylation at Ser2808 in the cardiac ryanodine receptor (RyR2), we generated knockin mice with a single amino acid substitution Ser à Ala (S2808A) in RyR2. We investigated the inotropic response of S2808 mice to isoproterenol (ISO) stimulation in vivo by LV hemodynamics and echocardiography, and characterized the in vivo mechanisms at the single-channel level.
Results: RyR2-S2808A channels from mouse hearts resembled wild-type (WT) RyR2 under unstimulated conditions but could not be PKA phosphorylated during β-adrenergic stimulation in vivo. RyR2-S2808A heterozygous and homozygous knockin mice showed no difference in left ventricular dimensions or ejection fraction (EF) as compared to WT control. Hemodynamic measurements confirmed that baseline contractility, LV systolic pressure and cardiac output were normal. Incremental ISO doses (5 to 100 ng/kg/min) resulted in diminished contractile response measured as end-systolic elastance (Ees) compared to WT (see table⇓). RyR2-Ser2808 PKA phosphorylation was absent in S2808A homozygous and significantly decreased in heterozygous mice and calstabin2 dissociation was significantly decreased during ISO in S2808A mice.
Conclusion: RyR2-Ser2808 represents a functionally important PKA phosphorylation site and plays a major role in β-adrenergic adaptation to sympathetic stress in vivo.