Effects of Zinc Protoporphyrin IX, a Heme Oxygenase Inhibitor, on Mitochondrial Membrane Potential in Rat Cultured Hepatocytes

Carbon monoxide (CO), a product of heme oxygenase, is released spontaneously from the liver and serves as an endogenous modulator of hepatobiliary function, although the whole mechanisms remain unknown. This study aimed to examine whether CO generated spontaneously might modulate hepatocellular function through its active interaction with the mitochondrial respiratory chain. Livers from male Wistar rats were used to provide isolated hepatocytes in culture using a collagenase perfusion technique. Endogenous CO production was abolished by application of 1 µM zinc protoporphyrin IX (ZnPP), a heme oxygenase inhibitor. When the hepatocytes contained in the suspension were observed by laser confocal digital microfluorography assisted by rhodamine 123, a fluorochrome sensitive to mitochondrial inner membrane potential (ΔΨ), the ZnPP application evoked a significant increase in the fluorescence, suggesting the increasing ΔΨ values. These results suggest that CO endogenously generated by heme oxygenase modulates hepatocyte function, at least in part, through changing mitochondrial membrane potential.