Copyright © 2007, European Society of Cardiology
Intermittent activation of bradykinin B2 receptors and mitochondrial KATP channels trigger cardiac postconditioning through redox signaling
aDipartimento di Scienze Cliniche e Biologiche, dell'Università di Torino, Italy
bDipartimento di Neuroscienze (sez. Fisiologia) dell'Università di Torino, Italy
* Corresponding author. Dipartimento di Scienze Cliniche e Biologiche, Università di Torino, Regione Gonzole 10, 10043 ORBASSANO (TO), Italy. Tel.: +39 11 6705430/7710; fax: +39 11 9038639. pasquale.pagliaro{at}unito.it
Objective Postconditioning (PostC) maneuvers allow post-ischemic accumulation of autacoids, which trigger protection. We tested if PostC-triggering includes bradykinin (BK) B2 receptor activation and its downstream pathway.
Methods and results Isolated rat hearts underwent 30 min ischemia and 120 min reperfusion. Infarct size was evaluated using nitro-blue tetrazolium staining. In Control hearts infarct size was 61±5% of risk area. PostC (5 cycles of 10 s reperfusion/ischemia) reduced infarct size to 22±4% (p<0.01). PostC protection was abolished by B2 BK receptor-antagonists (HOE140 or WIN64338), nitric oxide synthase-inhibitor (L-nitro-arginine-methylester), protein kinase G (PKG)-blocker (8-bromoguanosine-3',5'-cyclic-monophosphorothioate), and mitochondrial KATP (mKATP)-blocker (5-hydroxydecanoate) each given for 3 min only. Since 3 min of BK-infusion (100 nM) did not reproduce PostC protection, protocols with Intermittent-BK infusion were used to mimic PostC: a) 5 cycles of 10 s oxygenated-no-BK/oxygenated+BK buffer; b) 5 cycles of 10 s oxygenated-no-BK/hypoxic+BK buffer. Both protocols with Intermittent-BK attenuated infarct size (36±5% and 38±4%, respectively; p<0.05 vs Control and NS vs PostC for both; NS vs each other). Intermittent-BK protection was abolished by the same antagonists used to prevent PostC protection. Intermittence of re-oxygenation only (5 cycles of 10 s oxygenated/hypoxic buffer) did not reproduce PostC. Yet, cardioprotection was triggered by intermittent mKATP activation with diazoxide, but not by intermittent reactive oxygen species (ROS) generation with purine/xanthine oxidase. ROS scavengers (N-acetyl-L-cysteine or 2-mercaptopropionylglycine), given for 3 min only, abolished PostC-, Intermittent BK-and diazoxide-induced protection.
Conclusions Intermittent targeting of specific cellular sites (i.e. BK B2 receptors and mKATP channels) during early reperfusion triggers PostC protection via ROS signaling. Since neither intermittent oxygenation nor exogenous ROS generators can trigger protection, it is likely that intermittent autacoid accumulation and ROS compartmentalization may play a pivotal role in PostC-triggering.
KEYWORDS Ischemia-reperfusion injury; Nitric oxide; KATP channel; Postconditioning; Redox signaling
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