Mitochondria of retinal Muller (Glial) cells: The effects of aging and of application of free radical scavengers

Age-related changes of mitochondria were studied in Muller (retinal glial) cells from guinea pigs fed with or without externally applied Ginkgo biloba extract EGb 761, an established radical scavenger. When Muller cell mitoch ondria from aged animals were compared with those from young adults, they d isplayed (1) a diminished number of well-defined cristae at the ultrastruct ural level, (2) a reduced membrane potential, as revealed by fluorimetry us ing the voltage-sensitive dye tetramethyl rhodamine methylester, and (3) a slightly reduced index of vitality assayed by tetrazolium salt cole ri metr y. Muller cell mitochondria were also studied in aged guinea pigs which had been fed daily by EGb 761 during the last 2 months before they were sacrif iced. Such mitochondria displayed (1) many well-defined cristae at the ultr astructural level, and, compared with mitochondria from untreated aged anim als, (2) a significantly enhanced membrane potential and (3) a significantl y enhanced index of vitality. No age- or drug-related changes were observed in the mitochondrial content of GABA transaminase, as revealed by immunocy tochemistry/densitometry. These results suggest that many but not all struc tural and functional parameters of aging Muller cell mitochondria are impai red by accumulating oxidative damage, and that externally applied radical s cavengers may protect the organelles from the damaging actions of free radi cals. As it has been shown earlier that EGb 761 treatment enhances the intr insic glutathione content of aged guinea pig Muller cells, the protective r adical-scavenging effect of the drug may be mediated both directly and indi rectly. Copyright (C) 2000 S. Karger AG. Basel.