Myo-inositol transport in the lens of galactose-maintained rats.
Lens myo-inositol (MI) content is regulated by a pump-leak system consisting of an active Na-dependent MI transport and its passive permeability through the membrane. We measured the active MI uptake and membrane permeability in lenses of rats maintained on a 50% galactose diet for 1, 3 and 7 days. After only 1 day of galactose feeding, active MI uptake in the lens was reduced dramatically by 74% compared to age-matched control lenses; by day 3, active MI transport was decreased by 89% and it was undetectable by day 7. The passive membrane permeability was determined by measuring (a) the passive MI influx and (b) the 3H-sorbitol flux. After 1 day of galactose feeding, the membrane permeability increased such that within 3 days it increased to 5-6 fold. Galactose feeding also led to a rapid increase in lens polyol content. After 1 day, lens polyol increased to 53 mumol/g wet wt compared to a control value of 0.35 mumol/g wet wt and increased further to 65 and 72 mumol/g wet wt after 3 and 7 days of galactose feeding respectively. Lens galactose accumulation was low (3 mumol/g wet wt) up to 7 days; however, it was rapidly increased after 7 days. Our results indicate that galactose feeding rapidly interfered with MI homeostasis by a severe depression of active MI transport and a rapid increase in membrane permeability. These interferences of MI homeostasis correlate with the appearance of high polyol levels.
Beyer-Mears
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Department of Physiology, UMDNJ-New Jersey Medical School, Newark 07103-2714.
Diecke
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FP
Cruz
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Mistry
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K
D000818:Animals; D001693:Biological Transport, Active; D050260:Carbohydrate Metabolism; D002386:Cataract / Q000378:metabolism; D002463:Cell Membrane Permeability; D002849:Chromatography, Gas; D005690:Galactose / Q000494:pharmacology; D007294:Inositol / Q000493:pharmacokinetics*; D007908:Lens, Crystalline / Q000378:metabolism*; D008297:Male; D011108:Polymers / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013012:Sorbitol / Q000378:metabolism
D011108:Polymers; C024617:polyol; D007294:Inositol; D013012:Sorbitol; D005690:Galactose