Ocular Surface And Tear Film

The conjunctiva is a thin, mucus-secreting, vascular tissue that covers most of the inner surface of the eyelids, and is part of the anterior sclera where the cornea begins. The conjunctiva is thought to function as a passive physical protective barrier and to participate in the maintenance of tear-film stability due to the mucus secreted by the resident goblet cells (64). Our laboratory as well as others have provided ample evidence for additional functional features of the conjunctiva, viz....

Breakdown Of The Bloodretinal Barrier And Ion Channel Function

Although diabetes is the most common cause of breakdown in the endothelial barrier of the retinal vasculature, many other conditions are also associated with this sight-threatening phenomenon. In the case of diabetes, it appears that the upregulation of vascular endothelial growth factor (VEGF) results in the disruption of the endothelial tight junctions (41, 42) that limit the access of serum-derived molecules to the extracellular space of the retina. Because pericytes are positioned on the...

Ca2 Channels In The Retinal Pigment Epithelium

So far, voltage-dependent Ca2+ channels, a member of the TRP family of channels and ligand-gated Ca2+ channels have been identified in RPE cells (Fig. 1B). Of these channels, the voltage-dependent channels have been most extensively investigated. Early patch-clamp experiments with either freshly isolated or cultured RPE cells from rat and human indicated the functional presence of voltage-dependent Ca2+ channels in the RPE (64-72). These were identified as Ba2+ currents in whole-cell...

References

The Symposia on Calcium Binding Proteins and Calcium Function in Health and Disease an historical account, and an appraisal of their role in spreading the calcium message. Cell Calcium 2005 37 279-81. 2. Carafoli E. Calcium-a universal carrier of biological signals. Delivered on 3 July 2003 at the Special FEBS Meeting in Brussels. FEBS J 2005 272 1073-89. 3. Williams RJ. Calcium ions their ligands and their functions. Biochem Soc Symp 1974 133-8. 4. Williams RJ. Calcium-binding...

Effects Of Diabetes On Microvascular Kir Channels

The recent development of a technique to isolate viable pericyte-containing microvessels from the retinas of normal and diabetic rats has facilitated the quest to elucidate the mechanisms by which diabetes alters microvascular function. With freshly isolated microvessels, it is feasible to monitor pericyte currents via patch-pipettes, measure pericyte calcium levels with fura-2, and visualize pericyte contractions and lumen constrictions using time-lapse photography. Thus, retinal microvessels...

Vitamin C Transporters In The Retina

The blood-retinal barrier consists of retinal capillary endothelial cells (inner blood-retinal barrier) and the retinal pigment epithelium (outer blood-retinal barrier). The inner two-thirds of the neural retina gets its nutrient supply via transfer across the inner blood-retinal barrier. The remainder of the retina is nourished via transfer across the outer blood-retinal barrier. The endothelial cells, which constitute the inner blood-retinal barrier, form tight junctions and thus are...

Localization Of Gat1 In The Retina

Following the cloning of GAT-1 from the rat brain (58), its expression in the rat retina, together with GAT-2 and GAT-3 expression, was first demonstrated with polymerase chain reaction analysis in 1992 (49). Subsequently, the presence of GAT-1 in retinas of other vertebrates has been investigated. For instance, a skate GABA transporter displaying high homology with the mouse GAT-1 has been detected by Northern blot in the skate retina (59), and GAT-1 immunoreactivity has been observed by...

Adnan Dibas and Thomas Yorio

Transport of Nutrients and Ions from the Subretinal Space to the Choriocapillaris Mechanism of Transport of Ions in Retinal Pigment Epithelium The Na+,K+-ATPase pump K+ and Na+ Channels Cl Channels Agonists Enhancing Function of Calcium-activated Cl Channels Na+ Ca2+ Exchanger Functions in RPE to Reduce Ca2+ i and Antagonizes Calcium-Activated K+ and Cl Channels Electroneutral Cation-C1 Cotransporters (SLC12) Regulation of Cl and the Relationship with Bicarbonate Transporters Bicarbonate...

Nanosystems And Fundamentals Of Nanotechnology

Nanosystems include (i) soluble macromolecules, (ii) dendrimers, (iii) micelles, (iv) nanoplexes, (v) nanoparticles (nanospheres and nanocapsules), (vi) liposomes, and (vii) nanorods, tubes, and libers, among others. Some of these systems are shown in Fig. 1. From Ophthalmology Research Ocular Transporters in Ophthalmic Diseases and Drug Delivery Edited by J. Tombran-Tink and C. J. Barnstable Humana Press, Totowa, NJ Table 1 Biomedical nanosystems marketed for human use Product name Company...

Molecular Identity And Functional Features Of Vitamin C Transporters

The reduced form of vitamin C, ascorbate, is a monovalent anion at physiologic pH hence, it cannot diffuse across the hydrophobic lipid bilayer of the plasma membrane. Furthermore, the inside-negative membrane potential, which exists across the plasma membrane of cells, acts as a barrier for diffusion of ascorbate. This necessitates involvement of specific transport systems for the entry of ascorbate. Two different transporters have been identified at the molecular level for the transport of...

Regulation Of Retinal Pigment Epithelium Transport By Hormones And Agonists

RPE is unique in its regulation of ion transport by autocrine and exocrine factors. For example, growth factors, pyrimidines and changes in tonicity could trigger ATP release into the subretinal space. Apical ATP (or UTP) increases Ca2+ , and basolateral membrane Cl-conductance, while decreased apical membrane K+ conductance, a response that is blocked by the P2-purinoceptor blockers suramin and DIDS (138). Activation of P2Y(2) receptors in vivo directly stimulates rabbit RPE active transport...

Physicochemical Properties Of Drugs Affecting Permeability Across Ocular Barriers

Drug permeability prediction across the ocular tissues is important in the development of new drugs and drug-delivery strategies. To develop models that broadly predict permeability, it is necessary to understand the effects of various physicochemical properties of a drug, such as lipophilicity, charge, molecular radius and size, on its transport across ocular barriers. The cornea is composed of five or six layers of columnar epithelium with tight junction proteins. On the other hand, passive...