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H.M. Jernigan, Y. Su, W. Hu, I. Chakrabarti; Effect of Galactosemic Cataractogenesis on Sphingomyelin Synthesis in Rat Lens . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3474.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: This study examines the effect of galactosemia on the biosynthesis of the phospholipid (P-lipid) sphingomyelin (SM) in rat lenses. Previous studies using [3H]choline have shown that the rate of synthesis of total choline P-lipids in lenses from galactosemic rats exceeds that in control lenses, and that most of the resulting radiolabeled P-lipid is phosphatidylcholine (PtdC). We measured the transfer of radiolabel from PtdC to SM to determine whether the rate of SM synthesis also increases during cataractogenesis in galactosemic rat lenses. Methods: Rats were fed either a 50% galactose diet or a control diet (50% starch) for up to 8 days. Their intact lenses (8/group) were incubated in TC-199 medium with 2 µCi/ml of [3H]choline for up to 72 hr. P-lipids were extracted and separated by thin-layer chromatography, then the PtdC and SM fractions were analyzed for radiolabel by scintillation counting. Data are expressed as mean (± SEM). Results: In 4 hr, 3000 (± 350) dpm/lens were incorporated into PtdC by control lenses and 7760 (± 2680) dpm by 6-day galactosemic lenses, but no measurable 3H was found in SM. However, [3H]SM was measurable after 24 hr, and in 72 hr reached 2060 (± 180) dpm in control lenses and 11,600 (± 3600) dpm in 6-day galactosemic lenses, compared with 157,000 (± 7600) and 449,000 (± 45,000), respectively, in PtdC. In another experiment, after 48 hr of incubation with [3H]choline, the [3H]SM in 0 (control), 2, 4, 6, and 8- day galactosemic lenses was, respectively, 1.55 (± 0.07), 2.13 (± 0.72), 1.87 (± 0.13), 2.45 (± 0.50), and 2.60 (± 0.27) percent of the total radiolabeled P-lipid. After 72 hr of incubation, [3H]SM in 0, 2, 4, 6, and 8- day galactosemic lenses was 1.75 (± 0.08), 2.97 (± 0.50), 2.77 (± 0.42), 2.46 (± 0.36), and 3.57 (± 0.60) percent of the total radiolabeled P-lipid. Conclusions: SM, like PtdC, is synthesized at an increased rate during cataractogenesis in galactosemic rat lenses. This increased rate of phospholipid biosynthesis may represent a repair response to the osmotic stress induced by galactosemic cataractogenesis.
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