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M Shahidullah, C Butt, WS Wilson, M Yap, C-H To; Effects of Ion Transport and Channel-blocking Drugs on Aqueous Humor Formation in Bovine Isolated Eye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):901.
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Purpose: The purpose of the research was to investigate the role of active chloride secretion by the ciliary body in the formation of aqueous humor using the in vitro perfused eye which mimics the in vivo situation. Methods: Bovine eyes collected from the abattoir were cannulated through the ophthalmic artery and perfused with oxygenated Krebs’ solution at 37º C. Aqueous humor formation was measured by fluorescein dilution technique. Drugs were added to the perfusate and/or to the anterior chamber. Results: Na,K-ATPase inhibitor, ouabain (0.1mM), produced a significant reduction in aqueous humor formation (33%) when added to stromal or aqueous side. A ten fold increase in concentration (1.0mM) produced a reduction of 46% and 42 % when added to stromal or aqueous side respectively. When added to both sides (1.0mM), it produced a reduction of 61%. This results suggest that most of the aqueous humor in the in vitro eye is formed by active transport dependent on Na,K-ATPase. Bumetanide (0.1mM), a specific inhibitor of Na-K-2Cl cotransport, and furosemide (0.1mM), a non-specific anion transport inhibitor, produced 34% and 45% reduction when applied to the stromal side. DIDS (0.001 to 0.1mM) which is believed to inhibit the Cl-HCO3 exchanger, Na-HCO3 cotransporter and chloride channel, produced a dose-dependent reduction when added to the stromal side. The inhibition was 55% by the highest concentration used. Acetazolamide (0.1mM), a carbonic anhydrase inhibitor, applied to the blood side, produced 31% reduction. NPPB (0.1mM), the chloride channel blocker at the non-pigmented cells, produced 25% reduction when applied to the aqueous side. Conclusion: In the bovine eye the aqueous humour is formed mostly by processes involving active secretion. Transport of anions through the ciliary epithelium, particularly the chloride ion, plays a crucial role in aqueous humor formation.
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