Ischemic preconditioning requires increases in reactive oxygen release independent of mitochondrial K+ channel activity

Mitochondrial ATP-sensitive K+ channels (mitoK(ATP)) mediate ischemic preconditioning, a cardioprotective procedure. MitoK(ATP) activity has been proposed to either enhance or prevent the release of reactive oxygen species. This study tested the redox effects of mitoK(ATP) in order to clarify the role of these channels during preconditioning. We found no evidence that mitoK(ATP) channels increase mitochondrial reactive oxygen species release directly. In addition, neither ischemic preconditioning nor the mitoK(ATP) agonist diazoxide increased antioxidant defenses. Furthermore, increases in reactive oxygen species observed during ischemic preconditioning were not inhibited by mitoK(ATP) antagonists, suggesting that they occur upstream of channel activity. Antioxidants were tested to verify if diazoxide-promoted ischemic protection was dependent on reactive oxygen species. N-Acetylcysteine proved to be an inadequate antioxidant for these tests since it directly interfered with the ability of diazoxide to activate mitoK(ATP). Catalase reversed the beneficial effect of preconditioning, but not of diazoxide, indicating that reactive oxygen species mediating preconditioning occur upstream of mitoK(ATP), Taken together, these results demonstrate that ischemic preconditioning increases reactive oxygen release independently of rnitoK(ATP) and suggest that the activity of this channel prevents oxidative reperfusion damage by decreasing reactive oxygen species production. (c) 2005 Elsevier Inc. All rights reserved.