Résumé
The translocation of eNOS from the cytosol to subsarcolemmal (SSM) and intermyofibrillar (IMF) mitochondrial subfractions has been recently reported as a key trigger of exercise training-induced cardioprotection. The cardiac response to exercise is determined by both intrinsic mechanical and extrinsic adrenergic-dependent signaling pathways. Whether eNOS translocation in response to a single bout of exercise is due to mechanical stretch of the cardiac muscle or adrenergic stress remains to be studied.
The aim of this work was to evaluate the impact of cardiac adrenergic or mechanical stress on the translocation of eNOS from the cytosol to the mitochondria.
Mechanical stress was obtained on isolated perfused hearts by adjusting the diastolic pressure at 5 (low-stretch) or 15 (high-stretch) mmHg. The β-adrenergic stress was induced in low or high-stretch isolated hearts perfused with 10nM Isoproterenol for 5min. The hearts were quick-frozen. The cytosolic, SSM, and IMF+Myofilaments subfractions were obtained by differential centrifugations. The level of eNOS was analyzed by Western blot.
High-stretch tended to increase the level of eNOS in both IMF and SSM subfractions without reaching statistical significance. In contrast, Isoproterenol stimulation increased markedly the level of eNOS both in SSM and IMF in low-stretch hearts, with no additional impact of high-stretch. These results suggest that β-adrenergic receptors stimulation rather than mechanical stress of the cardiac muscle can trigger the translocation of eNOS. These results obtained ex-vivo were confirmed in vivo by treating the rats with a single injection of Isoproterenol (1mg/kg, 30min) that increased the level of eNOS in mitochondrial subfractions.
In this preliminary work, we reported that myocardial acute adrenergic stress, rather than acute stretch, is associated with eNOS translocation from cytosol to mitochondrial subfractions. The role of the eNOS-NO pathway in the normal response of the heart to adrenergic stress remain however to be studied and will be the aim of further studies.