Vacuolar H+-ATPase in ocular ciliary epithelium.
The mechanisms controlling the production of aqueous humor and the regulation of intraocular pressure are poorly understood. Here, we provide evidence that a vacuolar H+-ATPase (V-ATPase) in the ocular ciliary epithelium is a key component of this process. In intracellular pH (pHi) measurements of isolated ciliary epithelium performed with 2',7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF), the selective V-ATPase inhibitor bafilomycin A1 slowed the recovery of pHi in response to acute intracellular acidification, demonstrating the presence of V-ATPase in the plasma membrane. In isolated rabbit ciliary body preparations examined under voltage-clamped conditions, bafilomycin A1 produced a concentration-dependent decrease in short-circuit current, and topical application of bafilomycin A1 reduced intraocular pressure in rabbits, indicating an essential role of the V-ATPase in ciliary epithelial ion transport. Immunocytochemistry utilizing antibodies specific for the B1 isoform of the V-ATPase 56-kDa subunit revealed localization of V-ATPase in both the plasma membrane and cytoplasm of the native ciliary epithelium in both rabbit and rat eye. The regional and subcellular distribution of V-ATPase in specific regions of the ciliary process was altered profoundly by isoproterenol and phorbol esters, suggesting that change in the intracellular distribution of the enzyme is a mechanism by which drugs, hormones, and neurotransmitters modify aqueous humor production.
Wax
M B
MB
Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA.
Saito
I
I
Tenkova
T
T
Krupin
T
T
Becker
B
B
Nelson
N
N
Brown
D
D
Gluck
S L
SL
D000818:Animals; D002924:Ciliary Body / Q000201:enzymology*; D004848:Epithelium / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D006180:Proton-Translocating ATPases / Q000032:analysis* / Q000378:metabolism; D011817:Rabbits; D051381:Rats
D006180:Proton-Translocating ATPases