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(Investigative Ophthalmology and Visual Science. 2004;45:4529-4534.)
© 2004 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.04-0919
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Taurine Uptake by Human Retinal Pigment Epithelium: Implications for the Transport of Small Solutes between the Choroid and the Outer Retina

Jost Hillenkamp,1 Ali A. Hussain,1 Timothy L. Jackson,1 Joanna R. Cunningham,2 and John Marshall1

1From the Departments of Ophthalmology and 2Pharmacology, The Rayne Institute, St. Thomas’ Hospital, London, United Kingdom.

PURPOSE. To characterize the Michaelis-Menten kinetics of the taurine transporter (TT) in retinal pigment epithelium (RPE) freshly isolated from human donor eyes. To identify the rate limiting compartment in the pathway of taurine delivery from the choroidal blood supply to the outer retina composed by Bruch’s-choroid (BC) and the RPE in the human older age group.

METHODS. In human donor samples (4 melanoma-affected eyes, and 14 control eyes; age range, 62–93 years), radiochemical techniques were used to determine the RPE taurine accumulation at various exogenous concentrations. The transport capability of human RPE was obtained from a kinetic analysis of the high-affinity carrier over a substrate concentration of 1 to 60 µM taurine.

RESULTS. Uptake of taurine into human RPE at a taurine concentration of 1 µM was independent of donor age (P > 0.05) and averaged at 2.83 ± 0.27 (SEM) pmol/10 minutes per 6-mm trephine. Taurine transport by human RPE was mediated by a high-affinity carrier of Km 50 µM and Vmax of 267 pmol/10 minutes per 5-mm disc.

CONCLUSIONS. In human donor RPE, uptake of taurine remained viable in the age range 62 to 93 years. Taurine transport rates in the RPE were lower than across the isolated BC complex, and thus the data suggest that the former compartment houses the rate-limiting step in the delivery of taurine to the outer retina.




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