Effects of ion transport and channel-blocking drugs on aqueous humor formation in isolated bovine eye.
OBJECTIVE
To investigate the role of active chloride secretion by the ciliary epithelium in the formation of aqueous humor (AH), by using the in vitro perfused eye.


METHODS
Bovine eyes collected from an abattoir were cannulated through the ophthalmic artery and perfused with oxygenated Krebs' solution at 37 degrees C. Aqueous humor formation (AHF) was measured by the fluorescein-dilution technique. Drugs were added to the perfusate and/or to the anterior chamber.


RESULTS
NaK-adenosine triphosphatase (ATPase) inhibitor, ouabain (1.0 mM), produced a significant reduction in AHF by 46% and 42% when added to the stromal or aqueous side, respectively. When added to both sides (1.0 mM), it produced a reduction of 61%. Bumetanide (0.1 mM), a specific inhibitor of Na-K-2Cl cotransport, and furosemide (0.1 mM), a nonspecific anion transport inhibitor, produced 35% and 45% reductions when applied to the stromal side. DIDS (0.001-0.1 mM), which is believed to inhibit the Cl-HCO(3) exchanger, Na-HCO(3) cotransporter, and chloride channel, produced a dose-dependent reduction when added to the stromal side. The inhibition was 55% by the highest concentration used. 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB; 0.1 mM), a chloride channel blocker in the nonpigmented cells, produced a 25% reduction when applied to the aqueous side. Acetazolamide (0.1 mM), a carbonic anhydrase inhibitor, applied to the stromal side, produced 31% reduction.


CONCLUSIONS
At least 60% of the AH is formed by active secretion in bovine eyes. Transport of anions through the ciliary epithelium (CE), particularly the chloride ion, plays a crucial role in AHF.
Shahidullah
Mohammad
M
Laboratory of Experimental Optometry, Department of Optometry and Radiography, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
Wilson
William S
WS
Yap
Maurice
M
To
Chi-ho
CH
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology; D002417:Cattle; D002712:Chlorides / Q000502:physiology; D002924:Ciliary Body / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D015590:Fluorophotometry; D005665:Furosemide / Q000494:pharmacology; D007429:Intraocular Pressure / Q000187:drug effects; D007473:Ion Channels / Q000187:drug effects*; D017136:Ion Transport / Q000187:drug effects*; D009579:Nitrobenzoates / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000378:metabolism*
D002712:Chlorides; D004232:Diuretics; D007473:Ion Channels; D009579:Nitrobenzoates; D002034:Bumetanide; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D010042:Ouabain; D005665:Furosemide; D000086:Acetazolamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid