Abstract 11917: Muscarinic Stimulation Facilitates SR Ca+2 Release by Increasing PKG Phosphorylation of RyR2 at Ser-2808 and Decreasing CaMKII Phosphorylation at Ser-2814
Autonomic regulation of SR Ca+2 release is critical for modulating cardiac performance to match physiologic demand. During heart failure (HF), autonomic balanced shifts to a dominant sympathetic state to increase fractional SR Ca+2 release. Although intended to be compensatory, this increase in sympathetic input causes increases in the frequency of proarrhythmic spontaneous SR Ca+2 release events. Interestingly, parasympathetic augmentation was recently shown to alleviate HF phenotypes by shifting autonomic balance away from sympathetic dominance. While the effects of sympathetic stimulation and mechanism behind their action on cardiomyocyte Ca+2 handling are relatively well established in health and disease, the modes of action and mechanisms of parasympathetic modulation of SR Ca+2 release are poorly defined. To address this question, we investigated the effects of the cholinergic agonist, carbachol (CCH), on Ca+2 handling (Fluo-4 FF AM) and protein phosphorylation levels in cardiomyocytes using a combination of pharmacological approaches and genetic mouse models. In settings of reduced SR Ca+2 load, exposure to the parasympathetic agonist CCH increased fractional Ca+2 release without affecting Ca+2 spark frequency in cardiomyocytes. Immunoblot measurements showed that this “efficient” mode of excitation-contraction (EC) coupling involves reciprocal changes in the phosphorylation state of RyR2. Specifically, CCH treatment of cardiomyocytes increased Ser-2808 phosphorylation, mediated by muscarinic receptor subtype 2 and activation of PKG. Conversely, CCH treatment was associated with dephosphorylation at Ser-2814 through activation of muscarinic receptor subtype 3 and decreased ROS-dependent activation of CaMKII. We further demonstrate that parasympathetic stimulation improved Ca+2 cycling efficiency in cardiomyocytes isolated from failing hearts by restoring altered RyR2 phosphorylation balance. These results suggest that parasympathetic stimulation initiates a novel mode of EC coupling in cardiomyocytes that enhances the efficiency of cardiac SR Ca+2 store mobilization during systolic Ca+2 release, while inhibiting pathologic diastolic Ca+2 leak.
Author Disclosures: H. Ho: None. A.E. Belevych: None. B. Liu: None. I.M. Bonilla: None. P.B. Radwanski: None. H.H. Valdivia: None. K. Schober: None. C.A. Carnes: None. S. Györke: None.
- © 2016 by American Heart Association, Inc.