Aqueous humour formation

Cole, David

doi:10.1007/bf00184135

Cited by 55 publications

(19 citation statements)

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“…Aqueous humor production requires active ion transport. The ciliary epithelium is a double layer with two cell types: the outer nonpigmented epithelial (NPE) layer and the inner pigmented epithelial (PE) layer, both of which exhibit properties of transporting epithelia (1)(2)(3)(4)(5)(6)(7)(8). The two cell layers have juxtaposed apical membranes (Fig.…”

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confidence: 99%

Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Wax

Saito

Tenkova

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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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 (pH i ) measurements of isolated ciliary epithelium performed with 2 ,7-biscarboxyethyl-5(6)-carboxyf luorescein (BCECF), the selective V-ATPase inhibitor bafilomycin A 1 slowed the recovery of pH i 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 A 1 produced a concentration-dependent decrease in short-circuit current, and topical application of bafilomycin A 1 reduced intraocular pressure in rabbits, indicating an essential role of the VATPase 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.

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confidence: 99%

Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Wax

Saito

Tenkova

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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“…Aqueous humour secretion is one of the most important functions of the ciliary epithelium (5,8,9). Generally, Ca++-ions has been recognized as one of the key ions in regulating cellular secretion in most of the secretory epithelium (7,18,34).…”

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Ultracytochemical localization of Ca++-ATPase activity in the epithelial cells of guinea pig ciliary body.

Yasubuchi

Ueno

Tsukahara

et al. 1985

Acta Histochem. Cytochem

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“…However, the value of the factor for the bovine ciliary body is unknown. The surface area of the ciliary processes in the rabbit has been estimated by Cole (1966) who reported that the degree of convolution was muchgreater at the tips than at the pars plana. Heestimated the average conversion factor to be about 6.5.…”

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confidence: 99%

“…An abnormally high intraocular pressure is frequently associated with the sight threatening eye disease, glaucoma (6). It is widely believed that a component of the aqueous humour is actively secreted by the ciliary epithelium of the ciliary body (4). The bilayer ciliary epithelium is composed of non-pigmented (NPE) and pigmented (PE) ciliary epithelial cells which form a functional syncytium which produces the aqueous humour.…”

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In vitro Bovine Ciliary Body/Epithelium in a Small Continuously Perfused Ussing Type Chamber.

Mok

Tse

et al. 1998

Cell Struct. Funct.

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ABSTRACT. Our goal is to assess the viability of an in vitro preparation of bovine ciliary body/epithelium (CBE) in a small volume Ussing-type chamber. A new small volume Ussing-type chamber with continuous perfusion was developed for bovine CBE. The trans-CBE electrical parameters were monitored and the electrical responses of the CBE to ouabain (1 and 0.01 mM) were recorded. The trans-CBE fluxes of [14C]-L-ascorbate and [3H]-L-glucose were also studied. The bovine CBEpreparation was stable inside the chamber in terms of its potential difference (PD), short circuit current (SCC) and trans-CBE resistance.They were -0.51 ±0.05 mV (aqueous side negative), -5.43±0.04 //Acm~2 and 94±2 Q.cm2 (mean±s.e.m., n=35), respectively.The preparation hyperpolarised when 0.01 mMouabain was administered to the aqueous side, depolarised when ouabain was applied to the stromal side.[3H]-L-glucose diffusion was about 74 nEq h~1cm~2 in either direction (n=12). Taking the area magnification factor of the CBEinto consideration, the diffusional L-glucose flux across the bovine CBEwas comparable to other tight epithelia. A significant net ascorbate flux (0.26 ± 0.05 nEq h~1cm~2, n=4, p<0.01) was found in the stroma to aqueous direction. Wehave developed a viable in vitro bovine CBE preparation which was (1) electrically stable, (2) responsive to ouabain, (3) tight to L-glucose diffusion, and (4) capable of actively secreting ascorbate. A net trans-CBE chloride transport (0.81 ±0.30 /*Eq h~1cm~2, n=12, p=0.01) from stromal to aqueous side was found in the present in vitro model under short-circuited conditions. The aqueous humour is important for the normal functioning of the eye. It not only supplies nutrients to the avascular crystalline lens and cornea but also maintains the intraocular pressure of the eye which is crucial for the optical system to function. An abnormally high intraocular pressure is frequently associated with the sight threatening eye disease, glaucoma (6). It is widely believed that a component of the aqueous humour is actively secreted by the ciliary epithelium of the ciliary body (4). The bilayer ciliary epithelium is composed of non-pigmented (NPE) and pigmented (PE) ciliary epithelial cells which form a functional syncytium which produces the aqueous humour. However, the ionic mechanism behind the production of aqueous humour is not fully understood. It is generally accepted that fluid secretion is driven by active transport of ions. The active ion flow creates an osmotic gradient by which bulk flow of water follows. Therefore in order to understand how aqueous humour is produced, it is important to identify any active ion transport across the ciliary epithelium. Electrophysiological techniques with Ussing-Zerahn type chambersaim to understand mechanisms of ion or substrate transport across cells and epithelia. Isolated mammalian iris ciliary body/epithelium preparations have been mountedin Ussing-type chambers previously (3, 8). Based on the positive polarity of the bovine ciliary epithelium on the aqueous side...

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Aqueous humour formation

Cited by 55 publications

References 202 publications

Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Ultracytochemical localization of Ca++-ATPase activity in the epithelial cells of guinea pig ciliary body.

In vitro Bovine Ciliary Body/Epithelium in a Small Continuously Perfused Ussing Type Chamber.

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Aqueous humour formation

Cited by 55 publications

References 202 publications

Vacuolar H + -ATPase in ocular ciliary epithelium

Vacuolar H + -ATPase in ocular ciliary epithelium

Ultracytochemical localization of Ca++-ATPase activity in the epithelial cells of guinea pig ciliary body.

In vitro Bovine Ciliary Body/Epithelium in a Small Continuously Perfused Ussing Type Chamber.

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Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Vacuolar H ⁺ -ATPase in ocular ciliary epithelium