Rapid mitochondrial repolarization upon reperfusion after cardiac ischemia

Abstract

The mitochondrial membrane potential (ΔΨm) drives oxidative phosphorylation and alterations contribute to cardiac pathologies, but real-time assessment of ΔΨm has not been possible. Here we describe noninvasive measurements using mitochondrial heme bL and bH absorbances, which rapidly respond to ΔΨm. 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 bL relative to total reduced heme b (fbL = bL/(bL + bH)) exhibits a sigmoidal relationship with ΔΨm. Extrapolating this relationship to the heart enabled estimation of ΔΨm as 166 ± 18 mV (n = 25, mean ± s.d.). We used this approach to assess how ΔΨm changes during ischemia–reperfusion injury, an unknown limiting the understanding of ischemia–reperfusion injury. In perfused hearts, ΔΨm 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.