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Bo Gao, Andreas Wenzel, Christian Grimm, Stephan R. Vavricka, Dietmar Benke, Peter J. Meier, Charlotte E. Remè; Localization of Organic Anion Transport Protein 2 in the Apical Region of Rat Retinal Pigment Epithelium. Invest. Ophthalmol. Vis. Sci. 2002;43(2):510-514.
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purpose. The organic anion transporting protein (Oatp)-2 has been cloned from
brain and retina. It mediates transport of many endogenous and
exogenous amphiphilic compounds across the plasma membrane in a
sodium-independent manner. In the brain it resides at the luminal and
abluminal membrane of the capillary endothelium and at the basolateral
membrane of the choroid plexus epithelium. In the liver, it is
expressed at the basolateral membrane of hepatocytes. Its exact
localization and function in the retina are unknown. Therefore, the
purposes of the present study were to determine the cellular and
subcellular localization and the potential functional aspects of Oatp2
in the retina.
methods. Oatp2 was detected in rat retinal tissue by immunofluorescence confocal
microscopy and by Western blot analysis, with a specific antibody. A Xenopus laevis oocyte expression system was used for
functional transport studies.
results. Oatp2 immunoreactivity was abundantly present at the apical microvilli
of the rat retinal pigment epithelium and to a lesser degree in small
retinal vessels. In the oocyte expression system, N-retinyl-N-retinylidene ethanolamine
(A2E), an unusual cationic, amphiphilic retinoid, exhibited competitive Cis inhibition of Oatp2-mediated digoxin transport with
an estimated K i of ∼37 μM.
conclusions. In rat retina, Oatp2 is localized at the interface between the pigment
epithelium and the photoreceptor outer segments. A2E is a competitive
inhibitor of Oatp2-mediated substrate transport, suggesting that A2E or
A2E-like compounds and some retinoids may be substrates for Oatp2
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