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Ascorbic acid uptake and metabolism by corneal endothelium
A M Bode1, S S Vanderpool, E C Carlson
1Department of Physiology, University of North Dakota, Grand Forks.
Investigative Ophthalmology & Visual Science
|July 1, 1991
Summary
Corneal endothelial cells efficiently uptake and reduce dehydro-ascorbic acid, providing a source of ascorbic acid for ocular protection against UV radiation. This process maintains the reduced state of ascorbic acid in the aqueous humor.
Area of Science:
- Ophthalmology
- Cell Biology
- Biochemistry
Background:
- Ascorbic acid (vitamin C) is crucial for protecting ocular tissues from UV radiation damage.
- Its concentration in ocular compartments suggests a protective role, but the mechanism of delivery to the cornea is not fully understood.
Purpose of the Study:
- To investigate the transport and metabolic properties of corneal endothelial cells for ascorbic acid delivery to the stroma.
- To determine if these cells can actively supply ascorbic acid to the cornea.
Main Methods:
- Cultured bovine corneal endothelial cells were incubated with 14C-labeled ascorbic acid and dehydro-L-ascorbic acid.
- Uptake rates were measured, and the effects of metabolic inhibitors (cyanide, iodoacetamide, ouabain) and energy metabolism intermediates were assessed.
Main Results:
- Corneal endothelial cells demonstrated a significantly higher uptake rate (at least seven times) for dehydro-L-ascorbic acid compared to ascorbic acid.
- Dehydro-L-ascorbic acid was rapidly reduced to ascorbic acid within the cells.
- Uptake of dehydro-L-ascorbic acid was inhibited by cyanide and iodoacetamide, suggesting an energy-dependent process.
Conclusions:
- Corneal endothelial cells possess the transport and metabolic machinery to uptake dehydro-L-ascorbic acid from the aqueous humor and reduce it to ascorbic acid.
- This mechanism provides a local source of ascorbic acid for corneal protection and helps maintain the reduced state of total ascorbic acid in the aqueous humor.