Acute myocardial infarction occurs in approximately 500,000 Americans each year. With the sudden occlusion of a coronary arterial branch the myocardium supplied by that branch is in danger of infarction. Current treatment is to restore the blood flow through the vessel by removing the thrombus either with a catheter or a thrombolytic drug. Unfortunately that can seldom be accomplished before a significant amount of myocardium has died. The primary goal of this application is to devise a strategy for protecting ischemic hearts and reduce the amount of contractile tissue that dies. To that end we are attempting to determine the mechanism of ischemic preconditioning, a naturally occurring phenomenon where the heart quickly adapts itself to become resistant to infarction following a short sublethal episode of myocardial ischemia and reperfusion. In past years of this grant we have had great success in identifying signal transduction pathways responsible for these adaptive changes. Most recently we have identified a novel pathway where occupation of Gi-coupled receptors cause ATP-sensitive potassium channels on the mitochondria (mKATP) to open causing the generation of reactive oxygen species (ROS). The ROS then activate downstream kinases whose target proteins effect the actual protection. In this grant period we propose to study this pathway in detail.
Six specific aims are proposed. The first will explore the coupling to the mKATP and ROS production of all surface receptors that have been associated with preconditioning. The second will test the role of Akt in the coupling between receptors and mKATP. This will be done by transfecting cardiomyocytes with a dominant negative Akt construct. The 3rd aim will explore the ability of PKG (cGMP-dependent protein kinase) to open mKATP. We find that adenosine receptors trigger preconditioning through different pathways than the other Gi-coupled receptors in the heart. The 4th aim will explore whether these differences extend to their coupling to PKC, tyrosine kinases, and p38MAP kinase in the cardiac cells. The 5th aim will test whether neonatal rat heart lacks mKATP as suggested by previous pharmacological studies. The 6th aim will test whether ROS from high levels of xanthine oxidase in rat heart can lead to non-receptor triggering of preconditioning in that species. ? ?
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