Reverse electron flow-mediated ROS generation in ischemia-damaged mitochondria: Role of complex I inhibition vs. depolarization of inner mitochondrial membrane

Background: The reverse electron flow-induced ROS generation (RFIR) is decreased in ischemia-damaged mitochondria. Cardiac ischemia leads to decreased complex I activity and depolarized inner mitochondrial membrane potential (Delta Psi) that are two key factors to affect the RFIR in isolated mitochondria. We asked if a partial inhibition of complex I activity without alteration of the Delta Psi is able to decrease the RFIR. Methods: Cardiac mitochondria were isolated from mouse heart (C57BL/6) with and without ischemia. The rate of H2O2 production from mitochondria was determined using amplex red coupled with horseradish peroxidase. Mitochondria were isolated from the mitochondrial-targeted STAT3 overexpressing mouse (MLS-STAT3E) to clarify the role of partial complex I inhibition in RFIR production. Results: The RFIR was decreased in ischemia-damaged mouse heart mitochondria with decreased complex I activity and depolarized Delta psi. However, the RFIR was not altered in the MLS-STAT3E heart mitochondria with complex I defect but without depolarization of the Delta psi. A slight depolarization of the Delta Psi in wild type mitochondria completely eliminated the RFIR. Conclusions: The mild uncoupling but not the partially decreased complex I activity contributes to the observed decrease in RFIR in ischemia-damaged mitochondria. General significance: The RFIR is less likely to be a key source of cardiac injury during reperfusion. (c) 2013 Elsevier B.V. All rights reserved.