Exercise Training Stabilizes Ryr2-Dependent Ca2+ Release In Post-Infarction Heart Failure

Aim: Dysfunction of the cardiac ryanodine receptor (RyR2) is an almost ubiquitous finding in animal models of heart failure (HF) and results in abnormal Ca2+ release in cardiomyocytes that contributes to contractile impairment and arrhythmias. We tested whether exercise training (ET), as recommended by current guidelines, had the potential to stabilize RyR2-dependent Ca2+ release in rats with post-myocardial infarction HF.Materials and Methods: We subjected male Wistar rats to left coronary artery ligation or sham operations. After 1 week, animals were characterized by echocardiography and randomized to high-intensity interval ET on treadmills or to sedentary behavior (SED). Running speed was adjusted based on a weekly VO2max test. We repeated echocardiography after 5 weeks of ET and harvested left ventricular cardiomyocytes for analysis of RyR2-dependent systolic and spontaneous Ca2+ release. Phosphoproteins were analyzed by Western blotting, and beta-adrenoceptor density was quantified by radioligand binding.Results: ET increased VO2max in HF-ET rats to 127% of HF-SED (P < 0.05). This coincided with attenuated spontaneous SR Ca2+ release in left ventricular cardiomyocytes from HF-ET but also reduced Ca2+ transient amplitude and slowed Ca2+ reuptake during adrenoceptor activation. However, ventricular diameter and fractional shortening were unaffected by ET. Analysis of Ca2+ homeostasis and major proteins involved in the regulation of SR Ca2+ release and reuptake could not explain the attenuated spontaneous SR Ca2+ release or reduced Ca2+ transient amplitude. Importantly, measurements of beta-adrenoceptors showed a normalization of beta(1)-adrenoceptor density and beta(1):beta(2)-adrenoceptor ratio in HF-ET.Conclusion: ET increased aerobic capacity in post-myocardial infarction HF rats and stabilized RyR2-dependent Ca2+ release. Our data show that these effects of ET can be gained without major alterations in SR Ca2+ regulatory proteins and indicate that future studies should include upstream parts of the sympathetic signaling pathway.