Ischemic preconditioning preserves mitochondrial membrane potential and limits reactive oxygen species production

Background: Mitochondrial superoxide radical (O-2(center dot)) production increases after cardiac ischemia/reperfusion (IR). Ischemic preconditioning (IPC) preserves mitochondrial function and attenuates O-2(center dot) production, but the mechanism is unknown. Mitochondrial membrane potential (m Delta psi) is known to affect O-2(center dot) production; mitochondrial depolarization decreases O-2(center dot) formation. We examined the relationship between O-2(center dot) production and m Delta psi during IR and IPC. Materials/methods: Rat hearts were subjected to Control or IPC. Mitochondria were isolated at end equilibration (End EQ), end ischemia (End I), and end reperfusion (End RP). m Delta psi was measured using a tetraphenylphosphonium electrode. Mitochondrial O-2(center dot) production was measured by electron paramagnetic resonance using DMPO spin trap. Cytochrome c levels were measured using high- pressure liquid chromatography. Results: IPC preserved m Delta psi at End I (-156 +/- 5 versus -131 +/- 6 mV, P < 0.001) and End RP (-168 +/- 2 versus -155 +/- 2 mV, P < 0.05). At End RP, IPC attenuated O-2(center dot) production (2527 +/- 221 versus 3523 +/- 250 AU/mg protein, P < 0.05). IPC preserved cytochrome c levels (351 +/- 14 versus 269 +/- 16 picomoles/mg protein, P < 0.05) at End RP, and decreased mitochondrial cristae disruption (10% +/- 4% versus 33% +/- 7%, P < 0.05) and amorphous density formation (18% +/- 4% versus 28% +/- 1%, P < 0.05). Conclusion: We conclude that IPC preserves m Delta psi, possibly by limiting disruption of mitochondrial inner membrane. IPC also decreases mitochondrial O-2(center dot) production and preserves mitochondrial ultrastructure after IR. While it was previously held that slight decreases in m Delta psi decrease O-2(center dot) production, our results indicate that preservation of m Delta psi is associated with decreased O-2(center dot) and preservation of cardiac function in IPC. These findings indicate that the mechanism of IPC may not involve m Delta psi depolarization, but rather preservation of mitochondrial electrochemical potential. (C) 2012 Elsevier Inc. All rights reserved.