Studies on the eye lens in poikilothermal animals. I. Comparative studies on cation maintenance systems in rainbow trout and rat lenses

Biochemical analysis of young rats homozygous for the cataract mutation cat

Cataractogenesis was studied in young rats homozygous for the radiation-induced recessive cataract mutation cat. Homozygous cat/cat rats have reduced body weight (about two-thirds of the wild type) when 3 weeks old. The litter size is also diminished to about two-thirds of the wild type. For lens-specific parameters, as compared with homozygous wild type, the wet weight of the cataractous lenses is reduced, although the concentration of water-soluble lens proteins per wet weight is the same. No major alterations could be detected in the pattern of the water-soluble lens proteins separated by isoelectric focusing or gel electrophoresis run with or without mercaptoethanol. Additionally, no statistically significant alterations could be detected in the biochemical parameters of the lens used as indicators for osmotic stress (water content of the lens and the Na+-K+-dependent ATPase), for the energy state (ATP) and for the redox state (oxidized glutathione and superoxide dismutase). In contrast, the activity of transglutaminase is significantly enhanced in lenses as well as in the liver of young cat-rats, which might be understood as a biochemical marker for alterations in the developmental program. Cataractogenesis in the cat-rat is, therefore, suggested to be part of a syndrome including dwarfism and reduced litter size.

Effects of tannins on the oxidative damage of mouse ocular lens. I. Using the oxidative damage model induced by the xanthine-xanthine oxidase system

The protective effects of various tannins on ocular lens against the induced oxidative damage were examined. Oxidative damage on mouse lenses was induced by incubating them with xanthine-xanthine oxidase, ADP and Fe3+ (X.XOD system). X.XOD system caused an increase in lipid peroxide of lens membrane and decreases in Na,K-ATPase and GSH reductase activities in the lenses. After pretreatment of lenses with X.XOD system, the lenses were incubated with tannins in the medium containing no X.XOD system and the effects of tannins on biochemical parameters in the lenses were determined. Higher molecular tannins (penta-O-galloyl-beta-D-glucopyranose and geraniin) decreased the lipid peroxide in the lens and restored GSH content, Na,K-ATPase and GSH reductase activities in the lens to the level comparable to control. However, all of tannins tested restored much insufficiently the cation level (ratio of Na+/K+) in the lens regardless of extents of restoration of Na,K-ATPase level by them. Because it was supposed that tannins might act primarily on the plasma membrane, the effect of tannins on lens plasma membrane was examined using cell free system. Lens was homogenated and separated into membrane pellet and supernatant. When the pellet was treated with X.XOD system, the lipid peroxide in the pellet increased and its Na,K-ATPase activity decreased. In addition, the treated pellet decreased the GSH level and GSH reductase activity in the supernatant, when the pellet was combined with the supernatant. Higher molecular tannins reduced lipid peroxide content in the X.XOD-treated pellet to control level and the pellet in which lipid peroxide content was reduced by tannins caused much less decreases of GSH level and GSH reductase activity in the supernatant. These results suggest that, in intact lens, higher molecular tannins act on plasma membrane to eliminate lipid peroxide produced by the X.XOD system and consequently suppress the decreases in both Na,K-ATPase and GSH reductase activities without their entering inside the cell.

Studies on the eye lens in poikilothermal animals. II. Stimulation of anaerobic glycolysis in rainbow trout lenses incubated with Ca2+-free medium

The effects of Ca2+-free medium on cation levels and lactic acid production of rainbow trout lens incubated at various temperatures were examined in order to study passive cation transport system. Na+-K+ ratio (Na+/K+) increased when the lens was treated with Ca2+-free medium, but the effect of Ca2+-free medium was lowest between 15 and 20 degrees C which was the optimum water temperature for rainbow trout. Lactic acid production was stimulated between 15 and 20 degrees C in Ca2+-free medium. It was also stimulated at 37 degrees C in rat lenses incubated with Ca2+-free medium. However, the production was suppressed in ouabain-treated rainbow trout lenses. The suppression of Na+/K+ increase between 15 and 20 degrees C disappeared when the lens was treated with both Ca2+-free medium and ouabain. These results suggest that Na,K-ATPase activity and glycolysis were stimulated to prevent the increase of Na+/K+ in Ca2+-free medium. In addition, these results indicate that the optimum temperature was between 10 and 20 degrees C for the rainbow trout lens incubation in vitro, which is also the optimum water temperature in vivo.