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Rabbit corneal hydration and the bicarbonate pump.
1Department of Pharmacology, University of Bristol, School of Medical Sciences, Bristol, BS8 1TD, UK. J.S.Swan@Bristol.ac.uk
The Journal of Membrane Biology
|January 8, 2005
Summary
A metabolically driven bicarbonate current actively maintains corneal hydration by transporting ions across the corneal endothelium. This process is crucial for stabilizing stromal hydration at physiological levels.
Area of Science:
- Ocular Physiology
- Transport Physiology
Background:
- The corneal endothelium stabilizes corneal stroma hydration at physiological levels.
- Understanding the transport mechanisms is key to maintaining corneal health.
Purpose of the Study:
- To investigate the role of bicarbonate transport in maintaining corneal hydration at 22°C.
- To elucidate the electrogenic mechanisms underlying corneal endothelium function.
Main Methods:
- Experiments conducted on rabbit corneal endothelium at 22°C.
- Utilized Ussing-type chambers to measure electrical resistance and short-circuit current (s.c.c.).
- Tracer flux studies with H[14C]O3- and 86Rb to determine ion transport.
Main Results:
- Corneal swelling occurred when bicarbonate was omitted, reversible upon reintroduction.
- Ouabain inhibited the s.c.c. but not electrical resistance.
- Net bicarbonate flux into the aqueous humor correlated with s.c.c., suggesting an electrogenic bicarbonate current.
Conclusions:
- A metabolically driven electrogenic bicarbonate current is solely responsible for maintaining corneal hydration at 22°C.
- A model of active bicarbonate transport involving a sodium/bicarbonate cotransporter (NBC) and an apical anion channel is proposed.
- Discrepancies in bicarbonate flux at 35°C may relate to closed eye conditions.