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Effect of osmotic stress on phosphorylcholine efflux and turnover in rat lenses

Desouky, M.A.; Geller, A.M.; Jernigan, H.M.

Experimental Eye Research 54(2): 269-276

1992

ISSN/ISBN: 0014-4835
PMID: 1559554
Accession: 007255339

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Summary
The concentration of the phospholipid precursor, phosphorylcholine (P-choline), is greater than 10 mM in rat lenses. Cataratogenic osmotic or oxidative stress affects lenticular choline uptake and metabolism and decreases the P-choline concentration. To study the mehcanism(s) of the decrease in P-choline concentration induced by the cataractogenic sugars, xylose, galactose or glucose, rat lenses were first incubated in TC-199 medium containing [3H]choline, and then the metabolism of the resulting lenticular P-[3H]choline was followed in culture. Lenses which were osmotically stressed by incubation in TC-199 medium with 30 mM xylose lost more than 50% of their P-[3H]choline within 48 hr. Most of the P-[3H]choline lost from the stressed lenses was recovered in the incubation medium as P-[3H]choline, indicating that leakage of P-choline from the osmotically damaged lenses was the principal factor contributing to the decrease. Leakage of P-[3H]choline from lenses in the xylose medium was about three-fold greater than in the control medium, which contained 30 mM fructose. The turnover of the P-choline pool in rat lenses was also studied, and the concentration of P-choline was found to be a balance between hydrolysis and synthesis. The hydrolysis of lenticular P-choline was similar in xylose of control medium. In contrast, P-choline synthesis is slower in osmotically stressed lenses, resulting in a net conversion of P-[3H]choline to [3H]choline in the stressed lenses. Because some of the [3H]choline derived from P-choline hydrolysis was lost to the surrounding culture medium, this mechanism also contributed to the decreased P-choline in lenses incubated with xylose. Incorporaton of P-[3H]choline into phospholipids was slow (1% day-1) and phospholipid synthesis did not appear to be a major factor in the stress-induced changes in P-choline metabolism. Of the four sugars studied, xylose had the greatest effect in reducing rat lens P-choline, followed (in decreasing order) by galactose, glucose, and fructose.

References

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