title: Mitochondrial decay in hepatocytes from old rats: membrane potential declines, heterogeneity and oxidants increase.
abstract: Mitochondrial function during aging was assessed in isolated rat hepatocytes to avoid the problem of differential lysis when old, fragile mitochondria are isolated. Rhodamine 123, a fluorescent dye that accumulates in mitochondria on the basis of their membrane potential, was used as a probe to determine whether this key function is affected by aging. A marked fluorescent heterogeneity was observed in hepatocytes from old (20-28 months) but not young (3-5 months) rats, suggesting age-associated alterations in mitochondrial membrane potential, the driving force for ATP synthesis. Three distinct cell subpopulations were separated by centrifugal elutriation; each exhibited a unique rhodamine 123 fluorescence pattern, with the largest population from old rats having significantly lower fluorescence than that seen in young rats. This apparent age-associated alteration in mitochondrial membrane potential was confirmed by measurements with radioactive tetraphenylphosphonium bromide. Cells from young rats had a calculated membrane potential of -154 mV, in contrast to that of the three subpopulations from old rats of -70 mV (the largest population), -93 mV, and -154 mV. Production of oxidants was examined using 2',7'dichlorofluorescin, a dye that forms a fluorescent product upon oxidation. The largest cell subpopulation and a minor one from old animals produced significantly more oxidants than cells from young rats. To investigate the molecular cause(s) for the heterogeneity, we determined the levels of an age-associated mtDNA deletion. No significant differences were seen in the three subpopulations, indicating that the mitochondrial decay is due to other mutations, epigenetic changes, or both.
authors.affiliation: Division of Biochemistry and Molecular Biology, University of California, Berkeley 94720, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Hagen
authors.forename: D L
authors.initials: DL
authors.lastname: Yowe
authors.forename: J C
authors.initials: JC
authors.lastname: Bartholomew
authors.forename: C M
authors.initials: CM
authors.lastname: Wehr
authors.forename: K L
authors.initials: KL
authors.lastname: Do
authors.forename: J Y
authors.initials: JY
authors.lastname: Park
authors.forename: B N
authors.initials: BN
authors.lastname: Ames
mesh_terms: D000375:Aging / Q000378:metabolism; D000818:Animals; D004272:DNA, Mitochondrial; D005434:Flow Cytometry; D008297:Male; D008564:Membrane Potentials; D008930:Mitochondria, Liver / Q000378:metabolism* / Q000502:physiology; D016877:Oxidants / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D017384:Sequence Deletion
chemical_list: D004272:DNA, Mitochondrial; D016877:Oxidants; D010100:Oxygen