Suppression of membrane permeability transition in fetal rat liver mitochondria and its role in oxidative stress *
Because neonates are exposed to various hazards, such as oxidative stress during and immediately after labor, protective mechanisms should exist. However, to date, few have been identified. The aim of this study was to clarify the role of mitochondrial membrane permeability transition (MPT) in protection of the fetus and the neonate against the hazards arising during the perinatal period. Mitochondria were isolated from livers of fetal (FM) and adult (AM) rats by the method of Hogeboom. Cytochrome content and rates of oxidative phosphorylation were measured by spectrophotometric and polarographic methods, respectively. Mitochondrial MPT was measured by large amplitude swelling monitored by absorption at 540 nm and by depolarization of membrane potential monitored by fluorescence change in a cyanine dye, diS-C3- (5). Cytochrome c (Cyt. c) release from mitochondria was measured by Western blot analysis using anti-cytochrome c antibody. Caspase-3 activity was measured in a cell free system using a fluorogenic peptide substrate. No typical absorption spectrum of reduced Cyt. c was observed in FM although Cyt. c was detected by Western blotting. The rates of oxidative phosphorylation and the respiratory control ratio were lower in FM than in AM. Similarly, both mitochondrial MPT and Cyt. c release from FM induced by Ca2+ yielded lower values than those of AM. However, triton-treated FM supernatant activates caspase-3 like protease. These low levels of oxidative phosphorylation and MPT activity gradually became high after birth. The speed with which the high levels of oxidative phosphorylation and MPT were attained very rapid after exposure to oxygen stress. These results indicate that the low levels of MPT in FM might protect the fetus the apoptotic action of oxidative stress during the process of birth. The present results suggest that low levels of mitochondrial MPT and Cyt. c release and the consequent decrease in the activation of caspase-3, which induces chromosomal DNA fragmentation and apoptosis in liver cells, might contribute to protection of the tissues of both the fetus and the neonate against the various hazards experienced during the perinatal period. (Accepted on August 1, 2001) Kawasaki Igakkaishi 27(3) : 181-191, 2001
