Effect of osmotic stress on phosphorylcholine efflux and turnover in rat lenses.
The concentration of the phospholipid precursor, phosphorylcholine (P-choline), is greater than 10 mM in rat lenses. Cataractogenic osmotic or oxidative stress affects lenticular choline uptake and metabolism and decreases the P-choline concentration. To study the mechanism(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 or 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Desouky
M A
MA
Department of Ophthalmology, University of Tennessee, Memphis 38163.
Geller
A M
AM
Jernigan
H M
HM
D000818:Animals; D002794:Choline / Q000378:metabolism; D005449:Fluorenes / Q000494:pharmacology; D005690:Galactose / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006827:Hydantoins / Q000494:pharmacology; D007908:Lens, Crystalline / Q000378:metabolism*; D009924:Organ Culture Techniques; D009997:Osmotic Pressure; D010743:Phospholipids / Q000096:biosynthesis; D010767:Phosphorylcholine / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014994:Xylose / Q000494:pharmacology
D005449:Fluorenes; D006827:Hydantoins; D010743:Phospholipids; C052241:imirestat; D010767:Phosphorylcholine; D014994:Xylose; D005947:Glucose; D002794:Choline; D005690:Galactose