Late exercise training improves non-uniformity of transmural myocardial function in rats with ischaemic heart failure

Aims: The exercise-induced beneficial mechanisms after long-term myocardial infarction (MI) are incompletely understood. The present study evaluated the effect of treadmill exercise training (5 weeks), started at a late stage of heart failure (HF) (13 weeks post-MI), on rat left ventricle remodelling and dysfunction of the regional global and cellular contractile functions. Methods and results: In vivo echocardiography confirmed that sub-endocardial (ENDO) layers contract more (+86%) and faster (+50%) than the sub-epicardial (EPI) layers. This gradient was lost in MI rats due to a predominant reduction in the ENDO layer contractility. Exercise partially restored the amplitude and velocity of ENDO contraction, resulting in a partial recovery of the pump function indexed by the aortic blood-flow velocity time integral. At the cellular level, MI impaired ENDO contractile properties by reducing cell shortening (10-7%), calcium transient, and myofilament Ca²⁺ sensitivity. These alterations were normalized by exercise. Sarcoplasmic reticulum Ca ²⁺-ATPase (SERCA)2a expression and myosin light chain (MLC)-2 phosphorylation in ENDO cells were significantly reduced after MI and were restored by exercise. The EPI layer was only slightly reduced in vivo without cellular alterations. Conclusion: This study shows that exercise performed at a late stage after MI restored a transmural non-uniformity of myocardium lost during HF. Recoveries of Ca²⁺ homeostasis and myofilament function of cardiomyocytes contribute to this beneficial effect.