Spontaneous diastolic contractions and phosphorylation of the cardiac ryanodine receptor at serine-2808 in congestive heart failure in rat

Objective: The role of phosphorylation of the ryanodine receptor at serine-2808 (RyR(S2808)) in congestive heart failure (CHF) is controversial, and effects of RyRS2808 phosphorylation on contraction are unclear. It has been reported that diastolic sarcomere length (S,L) fluctuations accompany propagating contractile waves due to propagating SR Ca2+ release in trabeculae from rats with CHF. Here, we studied the influence of RyR destabilization by FK506 and isoproterenol on twitch force (F-tw) and SL fluctuations in right ventricular (RV) trabeculae. We measured phosphorylation of RyRS2808 in rats with myocardial infarction (MI) with or without beta-blockade and in rats during isoproterenol stimulation in order to assess the role of RyRS2808 phosphorylation in SL fluctuations in failing hearts. Methods: Five groups of male Lewis Brown-Norway rats were studied 3 months after M1: i) Sham; ii) MI with CHF (cMI); iii) MI without CHF; iv) metoprolol-treated MI, with and without CHF. The root mean square (RMSSL) of SL fluctuations in RV trabeculae was calculated. Results: RMSSL increased strongly both following a short train of stimuli at 2.5 Hz and following catecholamine activation in trabeculae from MI with CHF, resulting in a decrease in F-tw in proportion to RMSSL. RyR(S2808) phosphorylation was increased significantly in the left ventricle (LV; similar to 58%, P < 0.05) but not in the RV (n.s.) in M1 rats with CHF. FK506 tripled high frequency stimulation-induced RMSSL in nonfailing trabecula but did not further enhance RMSSL in failing trabecula. Isoproterenol increased RMSSL in nonfailing trabeculae only modestly despite a substantial increase in RyR(S2808) phosphorylation in the RV (similar to 60%, P < 0.05). Isoproterenol induced SL fluctuation without an increase in RV-RyR(S2808) phosphorylation in failing trabeculae. Chronic beta-blockade decreased high frequency and catecholamine stimulation-induced RMSSL while RyR(S2808) phosphorylation in the RV was indistinguishable from that in cMI. Conclusions: Acute RyR(S2808) phosphorylation by itself does not cause spontaneous contractile waves owing to RyR2 destabilization. Spontaneous contractile waves in CHF are not caused by RyRS2808 phosphorylation alone, suggesting that factors other than RyRS2808 phosphorylation affect RyR function. (c) 2005 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.