Abstract 185: Levels of Mitochondria ROS Production and Cardioprotection are Dependent on the Electron Transfer Chain Complex Stimulated in Ischemic Heart
Introduction: Mitochondrial ROS generation has been implicated in many pathologies including ischemia/reperfusion (I/R). Paradoxically, cardiac protection by preconditioning interventions can also lead to ROS production. We hypothesized that the increase in ROS -in injury as well as in protection-could be explained by differences in the production of ROS by stimulating mitochondrial electron transfer chain (ETC) activity with substrates of complexes I and II.
Methods and Results: Mitochondrial ROS generation was measured using amplex red and the mitochondria permeability transition pore opening measured by the calcium retention capacity (CRC) using calcium green. Specific substrates for complex I (glutamate/malate) and complex II (succinate), and the ETC inhibitors (rotenone and antimycin-A) were used. As expected when complex I substrate was used, mitochondria from I/R hearts and non-ischemic mitochondria treated with both inhibitors produced more ROS than control and preconditioned groups. Surprisingly, the substrate of complex II produced less ROS from I/R heart and in non-ischemic mitochondria treated with both inhibitors than control and preconditioned groups. Fresh mitochondria CRC was significantly higher in mitochondria treated with succinate compared to glutamate/malate (270±12 vs. 205±17nmol/mg of mitochondria prot, p<0.05).
Conclusions: The data demonstrates a dual production of ROS by the respiratory chain complexes depending on the type of complex being stimulated; being cardio-deleterious when complex I is stimulated because of the higher production of ROS in I/R mitochondria and cardio-protective after complex II stimulation associated with a lower production of ROS during injury. The higher ROS production when stimulating complex II may involve the inhibition of the opening of the mPTP, a key event of cell death by ischemia/reperfusion injury.
- © 2010 by American Heart Association, Inc.