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Opening mitoK_ATP increases superoxide generation from complex I of the electron transport chain

Department of Biology, Portland State University, Portland, Oregon

Submitted 15 March 2006 ; accepted in final form 12 June 2006

Opening the mitochondrial ATP-sensitive K⁺ channel (mitoK_ATP) increases levels of reactive oxygen species (ROS) in cardiomyocytes. This increase in ROS is necessary for cardioprotection against ischemia-reperfusion injury; however, the mechanism of mitoK_ATP-dependent stimulation of ROS production is unknown. We examined ROS production in suspensions of isolated rat heart and liver mitochondria, using fluorescent probes that are sensitive to hydrogen peroxide. When mitochondria were treated with the K_ATP channel openers diazoxide or cromakalim, their ROS production increased by 40–50%, and this effect was blocked by 5-hydroxydecanoate. ROS production exhibited a biphasic dependence on valinomycin concentration, with peak production occurring at valinomycin concentrations that catalyze about the same K⁺ influx as K_ATP channel openers. ROS production decreased with higher concentrations of valinomycin and with all concentrations of a classical protonophoretic uncoupler. Our studies show that the increase in ROS is due specifically to K⁺ influx into the matrix and is mediated by the attendant matrix alkalinization. Myxothiazol stimulated mitoK_ATP-dependent ROS production, whereas rotenone had no effect. This indicates that the superoxide originates in complex I (NADH:ubiquinone oxidoreductase) of the electron transport chain.

reactive oxygen species; mitochondrial ATP-sensitive potassium channel; signaling; protein kinase C

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