Role of Activation of Protein Kinase C in the Infarct SizeLimiting Effect of Ischemic Preconditioning Through Activation of Ecto-5′-nucleotidase

Abstract

BackgroundWe have reported previously that ischemic preconditioning limits infarct size by increasing ecto-5′-nucleotidase activity. Since we have also reported that protein kinase C activation increases ecto-5′-nucleotidase activity in rat cardiomyocytes, we tested whether activation of protein kinase C during ischemic preconditioning contributes to the infarct size–limiting effect through augmentation of ecto-5′-nucleotidase activity in the canine heart.Methods and ResultsThe coronary artery was occluded four times for 5 minutes with alternating 5-minute periods of reperfusion (ischemic preconditioning). Then the coronary artery was occluded for 90 minutes followed by 6 hours of reperfusion. Infarct size, normalized by the risk area, in the ischemic preconditioning group was smaller than in the control group (42.6±3.6% in the control group versus 7.9±1.8% in the ischemic preconditioning group,P<.001). Myocardial ecto-5′-nucleotidase activity was increased after the ischemic preconditioning procedure but the increase in ecto-5′-nucleotidase was attenuated by inhibitors of protein kinase C (polymyxin B and GF109203X). Both polymyxin B and GF109203X blunted the infarct size–limiting effect of ischemic preconditioning (infarct size 33.1±6.9% and 35.1±6.4%, respectively). The infarct size–limiting effect was also blunted by an inhibitor of ecto-5′-nucleotidase. Transient administration of methoxamine mimicked the increase in ecto-5′-nucleotidase activity and the infarct size–limiting effect, both of which were abolished by inhibitors of protein kinase C.ConclusionsWe conclude that activation of ecto-5′-nucleotidase and protein kinase C contributes to the infarct size–limiting effect of ischemic preconditioning.