Early preconditioning protection against stunning in conscious sheep. Role of KATP channels

Is there an effect of ischemic conditioning on myocardial contractile function following acute myocardial ischemia/reperfusion injury?

Ischemic conditioning induces cardioprotection; the final infarct size following a myocardial ischemic event is reduced. However, whether ischemic conditioning has long-term beneficial effects on myocardial contractile function following such an ischemic event needs further elucidation. To date, ex vivo studies have shown that ischemic conditioning improves the contractile recovery of isolated ventricular papillary muscle or atrial trabeculae following simulated ischemia. However, in vivo animal studies and studies in patients undergoing elective cardiac surgery show conflicting results. At the subcellular level, it is known that ischemic conditioning improved energy metabolism, preserved mitochondrial respiration, ATP production, and Ca²⁺ homeostasis in isolated mitochondria from the myocardium. Ischemic conditioning also presents with post-translational modifications of proteins in the contractile machinery of the myocardium. The beneficial effects on myocardial contractile function need further elucidation. This article is part of a Special Issue entitled: The power of metabolism: Linking energy supply and demand to contractile function edited by Torsten Doenst, Michael Schwarzer and Christine Des Rosiers.

Late cardiac preconditioning by exercise in dogs is mediated by mitochondrial potassium channels

We previously showed that exercise induces myocardial preconditioning in dogs and that early preconditioning is mediated through mitochondrial adenosine triphosphate-sensitive potassium channels. We decided to study if late preconditioning by exercise is also mediated through these channels. Forty-eight dogs, surgically instrumented and trained to run daily, were randomly assigned to 4 groups: (1) Nonpreconditioned dogs: under anesthesia, the coronary artery was occluded during 1 hour and then reperfused during 4.5 hours. (2) Late preconditioned dogs: similar to group 1, but the dogs run on the treadmill for 5 periods of 5 minutes each, 24 hours before the coronary occlusion. (3) Late preconditioned dogs plus 5-hydroxydecanoate (5HD): similar to group 2, but 5HD was administered before the coronary occlusion. (4) Nonpreconditioned dogs plus 5HD: similar to group 1, but 5HD was administered before the coronary occlusion. Infarct size (percent of the risk region) decreased by effect of exercise by 56% (P < 0.05), and this effect was abolished with 5HD. 5HD by itself did not modify infarct size. Exercise did not induce myocardial ischemia, and the hemodynamics during ischemia-reperfusion period did not differ among groups. These effects were independent of changes in collateral flow to the ischemic region. We concluded that late cardiac preconditioning by exercise is mediated through mitochondrial adenosine triphosphate-sensitive potassium channels.