Abstract
We have investigated the ability of Ca 2+ to induce the formation of high molecular weight (HMW) proteins in the intact lens. Ca 2+ cataracts were produced in rabbit lenses by culturing the lenses for either four days in medium containing 20 m m Ca 2+ or for three days in medium containing 100 m m Ca 2+. Lenses cultured in 20 and 100 m m Ca 2+ medium became opaque after 20 hr and contained 30 and 200 times higher levels of Ca 2+, respectively, than transparent lenses cultured in medium containing 1 m m Ca 2+. Lenses exposed to 100 m m Mg 2+ did not lose transparency. The opacification of the lenses extended to a depth of 1 mm into the cortical layer and did not involve the nucleus. No significant differences were found in the concentrations of either soluble or insoluble proteins present in freshly excised lenses and Ca 2+ cataracts. Soluble HMW proteins, > 1·5 × 10 6 daltons, were in two- and five-fold greater amounts in the 20 and 100 m m Ca 2+ cataraets, respectively, compared to controls. HMW protein present in the 100 m m Ca 2+ cataract amounted to approximately 3% of the total soluble protein in the lens. The amount of Ca 2+ present in the HMW fraction was 1 Ca 2+ per 5 × 10 5 daltons, no higher than that present in the unaggregated crystallins. No evidence was found for covalent bonding in the aggregate. Results of polyacrylamide gel electrophoresis and double immunodiffusion indicated the presence of α- and β- but not γ-crystallin in the HMW protein. This study indicates that an accumulation of Ca 2+ in the intact lens induces formation of HMW proteins which may be associated with the loss of lens transparency.
Published Version
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