Opening of Mitochondrial K _ATP Channels Triggers the Preconditioned State by Generating Free Radicals

Abstract

Abstract-The critical time for opening mitochondrial (mito) K ATP channels, putative end effectors of ischemic preconditioning (PC), was examined. In isolated rabbit hearts 29Ϯ3% of risk zone infarcted after 30 minutes of regional ischemia. Ischemic PC or 5-minute exposure to 10 mol/L diazoxide, a mito K ATP channel opener, reduced infarction to 3Ϯ1% and 8Ϯ1%, respectively. The mito K ATP channel closer 5-hydroxydecanoate (200 mol/L), bracketing either 5-minute PC ischemia or diazoxide infusion, blocked protection (24Ϯ3 and 28Ϯ6% infarction, respectively). However, 5-hydroxydecanoate starting 5 minutes before long ischemia did not affect protection. Glibenclamide (5 mol/L), another K ATP channel closer, blocked the protection by PC only when administered early. These data suggest that K ATP channel opening triggers protection but is not the final step. Five minutes of diazoxide followed by a 30-minute washout still reduced infarct size (8Ϯ3%), implying memory as seen with other PC triggers. The protection by diazoxide was not blocked by 5 mol/L chelerythrine, a protein kinase C antagonist, given either to bracket diazoxide infusion or just before the index ischemia. Bracketing preischemic exposure to diazoxide with 50 mol/L genistein, a tyrosine kinase antagonist, did not affect infarction, but genistein blocked the protection by diazoxide when administered shortly before the index ischemia. Thus, although it is not protein kinase C-dependent, the protection by diazoxide involves tyrosine kinase. Bracketing diazoxide perfusion with N-(2-mercaptopropionyl) glycine (300 mol/L) or Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (7 mol/L), each of which is a free radical scavenger, blocked protection, indicating that diazoxide triggers protection through free radicals. Therefore, mito K ATP channels are not the end effectors of protection, but rather their opening before ischemia generates free radicals that trigger entrance into a preconditioned state and activation of kinases. (Circ Res. 2000;87:460-466.)

Post-ischemic early acidosis in cardiac postconditioning modifies the activity of antioxidant enzymes, reduces nitration, and favors protein S-nitrosylation

“…A pivotal cardioprotective role for NO • from enzymatic and non-enzymatic origin has been shown for both pre and postconditioning [13,15,25,26,[46][47][48][49][50]60,66,69]. In fact, NO • is a cardiovascular protective molecule via multiple effects, both in normoxia and particularly during reperfusion [15,50,66].…”

“…Both in vivo and in vitro ischemic-and pharmacologicalpreconditioning triggering require protective ROS signaling. In fact, either ROS-generators or ROS-scavengers, given before the index ischemia, trigger or abolish preconditioning [2,7,10,16,23,43,47,48,61]. Therefore, ROS are double edge swords (ROS stress vs ROS signaling).…”

Efeitos da N-acetilcisteína no precondicionamento isquêmico: estudo em corações isolados de ratos

“…The release of oxygen free radicals (OFR) is a cause of myocardial lesion during post-ischemia reperfusion. Paradoxically, Pain et al [9] and Forbes et al [10] showed that the release of reactive oxygen species (ROS) participates in the protective mechanism of the IP by opening of mitoK + ATP channels and activation of kinases. N-acetylcysteine is classified as an antioxidant, but has broad clinical utility as a mucolitic agent, as antidote for acetaminophen poisoning, prevention of renal dysfunction by use of radiocontrasts and potentiator of hemodynamic effects of nitroglycerin.…”

“…Chen et al [12] noted that N-acetylcysteine blocked the loss of glutathione and the protective effect of IP, but its protocol with four cycles of 5 minutes of ischemia and reperfusion resulted in myocardial stunning before the sustained period of ischemia. Pain et al [9] proposed that the OFR had a paradoxical role in the protection provided by IP, encouraging us to study the effects of antioxidant Nacetylcysteine on the mechanism of IP in isolated rat hearts according Langendorff model. N-acetylcysteine has wide clinical use, and is used in many patients undergoing heart surgery.…”

Effect of inhibitors of NADPH oxidase complex and mitochondrial ATP‐sensitive potassium channels on generation of dopaminergic neurons from neurospheres of mesencephalic precursors

“…Furthermore, the results obtained with 5-HD were confirmed with glibenclamide, which acts as a general inhibitor of KATP channels. It has already shown that opening of mitoKATP channels is followed by an increase in ROS generation, and that this is reduced after blocking the channels with 5-HD or glibenclamide (Pain et al, 2000;Krenz et al, 2002;Andrukhiv et al, 2006).…”