Rapid mitochondrial repolarization upon reperfusion after cardiac ischemia

Abstract The mitochondrial membrane potential (ΔΨ m ) drives oxidative phosphorylation and alterations contribute to cardiac pathologies, but real-time assessment of ΔΨ m has not been possible. Here we describe noninvasive measurements using mitochondrial heme b L and b H absorbances, which rapidly respond to ΔΨ m . Multi-wavelength absorbance spectroscopy enabled their continuous monitoring in isolated mitochondria and the perfused heart. Calibration of heme b absorbance in isolated mitochondria revealed that reduced heme b L relative to total reduced heme b (f b L = b L /( b L + b H )) exhibits a sigmoidal relationship with ΔΨ m . Extrapolating this relationship to the heart enabled estimation of ΔΨ m as 166 ± 18 mV ( n = 25, mean ± s.d.). We used this approach to assess how ΔΨ m changes during ischemia–reperfusion injury, an unknown limiting the understanding of ischemia–reperfusion injury. In perfused hearts, ΔΨ m declined during ischemia and rapidly reestablished upon reperfusion, supported by oxidation of the succinate accumulated during ischemia. These findings expand our understanding of ischemia–reperfusion injury.