Tight Junctions of the Human Ciliary Epithelium: Regional Morphology and Implications on Transepithelial Resistance

Noske, W; Stamm, Catherine; Hirsch, M.

doi:10.1006/exer.1994.1092

Cited by 12 publications

(7 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The issue was resolved with the advent of freeze-fracture electron microscopy. Although regional variations in tight junction complexity were found, the literature was consistent in stating that both the non-pigmented ciliary epithelial cells and the endothelial cells of the iris vasculature were joined by continuous tight junctions (Raviola, 1974, Freddo and Raviola, 1982b, Noske, Stamm and Hirsch, 1994, Hirsch, Montcourrier, et al 1995)(Figure #1 – bottom). These direct views of tight junction structure were consistent with the vascular tracer studies showing that neither the ciliary epithelium, nor the iris vascular endothelium leaks plasma –proteins under normal conditions.…”

Section: Early Studies Of the Blood-aqueous Barriermentioning

confidence: 65%

A contemporary concept of the blood–aqueous barrier

Freddo

2013

Progress in Retinal and Eye Research

106

View full text Add to dashboard Cite

This review traces the evolution of the concept of the blood-aqueous barrier (BAB) during the past 20 years. The classical model simply stipulated that the tight junctions of the iris vasculature and ciliary epithelium excluded plasma proteins from the aqueous humor (AH). It failed to reconcile the presence of AH protein levels equal to 1% of that found in plasma. Moreover, models of barrier kinetics assumed that the processes of AH secretion and plasma protein entry were directly linked. Thus, elevations of AH protein levels could only be explained by a pathological breakdown of the BAB. Over the last 20 years it has been shown that the plasma proteins in normal AH by-pass the posterior chamber entirely. Instead, these proteins diffuse from the capillaries of ciliary body stroma, into the iris stroma and then into the anterior chamber. This creates a reservoir of plasma-proteins in the iris stroma that is not derived from the iris vessels. This reservoir is prevented from diffusing posteriorly by tight junctions in the posterior iris epithelium. The one-way valve created by the pupil resting on the anterior lens capsule, combined with the continuous, forward flow of AH through the pupil, prevents protein reflux into the posterior chamber. Importantly, in the new paradigm, secretion of AH and the entry of plasma proteins into AH, are semi-independent events. This opens the possibility that AH protein levels could increase in the absence of breakdown of the BAB. Clinical consequences of this new paradigm of the BAB are discussed.

show abstract

Section: Early Studies Of the Blood-aqueous Barriermentioning

confidence: 65%

A contemporary concept of the blood–aqueous barrier

Freddo

2013

Progress in Retinal and Eye Research

106

View full text Add to dashboard Cite

show abstract

“…There are two blood-retina barriers: tight junctions between the inner intraretinal capillary endothelial cells at the retinal ganglion cell layer protect the inner 2/3 of the retina, and tight junctions between the retinal pigment epithelial (RPE) cells form the barrier to the outer, fenestrated choroidal blood supply [17-19]. A third barrier in the eye, the blood-aqueous barrier, is formed by the tight junctions in the non-pigmented epithelium (NPE) of the ciliary body [20], where the Na,K-ATPase contributes to sodium and aqueous humor secretion [21]. …”

Section: Introductionmentioning

confidence: 99%

Na,K-ATPase alpha isoforms at the blood-cerebrospinal fluid-trigeminal nerve and blood-retina interfaces in the rat

Arakaki

McCleary

Techy

et al. 2013

Fluids Barriers CNS

View full text Add to dashboard Cite

BackgroundCerebrospinal fluid (CSF) sodium concentration increases during migraine attacks, and both CSF and vitreous humor sodium increase in the rat migraine model. The Na,K-ATPase is a probable source of these sodium fluxes. Since Na,K-ATPase isoforms have different locations and physiological roles, our objective was to establish which alpha isoforms are present at sites where sodium homeostasis is disrupted.MethodsSpecific Na,K-ATPase alpha isoforms were identified in rat tissues by immunohistochemistry at the blood-CSF barrier at the choroid plexus, at the blood-CSF-trigeminal barrier at the meninges, at the blood-retina barrier, and at the blood-aqueous barrier at the ciliary body. Calcitonin gene-related peptide (CGRP), occludin, or von Willibrand factor (vWF) were co-localized with Na,K-ATPase to identify trigeminal nociceptor fibers, tight junctions, and capillary endothelial cells respectively.ResultsThe Na,K-ATPase alpha-2 isoform is located on capillaries and intensely at nociceptive trigeminal nerve fibers at the meningeal blood-CSF-trigeminal barrier. Alpha-1 and −3 are lightly expressed on the trigeminal nerve fibers but not at capillaries. Alpha-2 is expressed at the blood-retina barriers and, with alpha-1, at the ciliary body blood aqueous barrier. Intense apical membrane alpha-1 was associated with moderate cytoplasmic alpha-2 expression at the choroid plexus blood-CSF barrier.ConclusionNa,K-ATPase alpha isoforms are present at the meningeal, choroid plexus, and retinal barriers. Alpha-2 predominates at the capillary endothelial cells in the meninges and retinal ganglion cell layer.

show abstract

“…Transepithelial resistance values in 25 preparations were 45 ohms.cm2 ± 2.0 (s.e.m. ), as previously published (9,11,12,13).…”

Section: Bilayer Flux Experimentsmentioning

confidence: 89%

Transepithelial Transport of Ascorbic Acid by the Isolated Intact Ciliary Epithelial Bilayer of the Rabbit Eye

Mead¹,

Sears²,

Sears³

1996

Journal of Ocular Pharmacology and Therapeutics

View full text Add to dashboard Cite

The purpose of these experiments was to test whether the isolated intact epithelial bilayer derived from rabbit ciliary processes transports ascorbic acid and to what degree the transport rate in vitro corresponds to the in vivo process. The intact ciliary epithelial bilayer of the rabbit eye isolated by perfusion was mounted in a particularly constructed Ussing type chamber. Fluxes were measured by additions of 14C ascorbate to the hemichamber on either the pigmented epithelium (PE) or the nonpigmented epithelium (NPE) side where equal concentrations of ascorbate from .02 to 2.0 mM were present. Samples were taken at intervals thereafter and counted in a liquid scintillation counter. The experiments were done under short circuit conditions to avoid the possible influence of fluctuating currents upon the movement of ascorbate. Like the earlier iris ciliary body preparations, separation of ascorbate fluxes is also done by the isolated intact ciliary epithelial bilayer, and the transport of ascorbic acid proceeds by saturation kinetics. The uptake process is accomplished entirely by the pigmented epithelium (PE). The Km of the process is 0.97 mM, and Vmax was valued at 130 nM/L/hr. Thus, assuming an aqueous flow rate of 2 microliters/min, the transfer of ascorbic acid across the bilayer occurs at a rate required to maintain the ordinary millimolar concentration of ascorbic acid in the aqueous humor found in vivo.

show abstract

Tight Junctions of the Human Ciliary Epithelium: Regional Morphology and Implications on Transepithelial Resistance

Cited by 12 publications

References 0 publications

A contemporary concept of the blood–aqueous barrier

A contemporary concept of the blood–aqueous barrier

Na,K-ATPase alpha isoforms at the blood-cerebrospinal fluid-trigeminal nerve and blood-retina interfaces in the rat

Transepithelial Transport of Ascorbic Acid by the Isolated Intact Ciliary Epithelial Bilayer of the Rabbit Eye

Contact Info

Product

Resources

About