Retinal pigment epithelium transport

Bailey, KR, Ishida, BY, Duncan, KG, Kane, JP, and Schwartz, DM, 2004. Basal reverse cholesterol transport of retinal pigment epithelium cell digested photoreceptor outer segment lipids. Invest Ophthalmol Vis Sci 45, U721. 

Wang, N and Anderson, RE, 1993. Transport of 22 6n-3 in the plasma and uptake into retinal pigment epithelium and retina. Exp Eye Res 57, 225-233. 

A variety of automatic voltage clamp devices with special modifications have been extensively utilized in electrophysiological studies of /sc in several ocular tissues including the amphibian corneal epithelium [42] and human fetal retinal pigment epithelium [43, 44], as well as non-ocular tissues like the rat tracheal epithelium [45], A strong temperature dependency and inhibitory effect of serosally instilled ouabain on the rabbit conjunctival /sc are characteristic of active ion transport driven by Na+/K+-ATPases in the conjunctiva [6, 7],... 

R. H. Quinn and S. S. Miller. Ion transport mechanisms in native human retinal pigment epithelium. Invest Ophthalmol Vis Sci 33 3513-3527 (1992)... 

The retinal pigmented epithelium (RPE) is in intimate, anatomic, and functional contact with the retina. Separated from the retina by Bruch s membrane, the RPE serves to regulate nutrients to the retina, phagocytize retinal debris, remove metabolic end products, and control the visual cycle. From a mass transport perspective, the RPE represents the outer BRB. 

Philp, N.J., et al. 2003. Polarized expression of monocarboxylate transporters in human retinal pigment epithelium and ARPE-19 cells. Invest Ophthalmol Vis Sci 44 1716. 

Under conditions of low light intensity, the all-trans-retinaldehyde released from rhodopsin is reduced to aU-fra s-retinol, which is then transported to the retinal pigment epithelium bound to the interphotoreceptor RBP. This protein also binds fatty acids, including palmitate and docosa-hexaenoic acid (C22 6 co3), which is known to be essential for vision and which comprises some 50% of the phospholipid of photoreceptor cells. 

In the retinal pigment epithelium, palmitate is bound to the fatty acid binding site of the interphotoreceptor RBP, and the retinoid binding site has a high affinity for 11 -ds-retinaldehyde, which is to be transported to the photoreceptor cells. In the photoreceptor cells, the palmitate is displaced by docosahex-aenoic acid, which causes a conformational change in the protein, so that it no longer binds 11 -ds-retinaldehyde, which is delivered to the photoreceptor cells and binds all-fraws-retinol for transport back to the pigment epithelium. Here, the docosahexaenoic acid is displaced by palmitate, and the affinity of the protein for 11-ds-retinaldehyde is restored (Palczewski and Saari, 1997 Tschanz and Noy, 1997). 

All-trans retinol then diffuses out of the outer segments (rod or cone) and into the retinal pigmented epithelium (RPE). The diffusion of all-trans-retinol out of the outer segments and into RPE cells is facilitated by interstitial retinoid binding protein (IRBP), which is localized in the extracellular matrix of the retina (22). IRBP binds all-trans-retinol as it diffuses out of the outer segment cells and is believed to facilitate transport of aM-trans-retinol to the RPE cell. Additionally, RPE cells directly acquire retinol from serum as described earlier. In both cases, retinol in the RPE cell is rapidly esterified by LRAT in a lecithin-dependent mechanism (22). Retinyl esters provide both a mechanism of storage for the RPE cell and/or provide a substrate for the isomerization reaction (22). 

S. R., Benke, D., Meier, P.J., and Reme, C.E. (2002) Localization of organic anion transport protein 2 in the apical region of rat retinal pigment epithelium. Investigative Ophthalmology eJ Visual Science, 43, 510-514. 

Yoon, H., Fanelli, A., GroUman, E.F., and Philp, N.J. (1997) Identification of a unique monocarboxylate transporter (MCT3) in retinal pigment epithelium. Biochemical and Biophysical Research Communications, 234, 90—94. 

Hughes BA, Gallemore RP, Miller SS. Transport mechanisms in the retinal pigment epithelium. In Marmor MF, Wolfensberger TJ, eds. The Retinal Pigment Epithelium. New York Oxford University Press, 1998 103-134. 

Peterson WM, Meggyesy C, Yu K, Miller SS. Extracellular ATP activates calcium signaling, ion, and fluid transport in retinal pigment epithelium. J Neurosci 1997 17 2324-2337. 

DiMattio, J., and Streitman, J., 1991, Active transport of ascorbic acid across the retinal pigment epithelium of the bullfrog, Curr. Eye Res. 10 959-965. 

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