title: Taurine uptake by human retinal pigment epithelium: implications for the transport of small solutes between the choroid and the outer retina.
abstract: OBJECTIVE
  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 microM taurine.
  
  
  RESULTS
  Uptake of taurine into human RPE at a taurine concentration of 1 microM 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 K(m) 50 microM and V(max) 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.
authors.affiliation: Department of Ophthalmology, The Rayne Institute, St. Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, UK. hillenka@hotmail.com
authors.forename: Jost
authors.initials: J
authors.lastname: Hillenkamp
authors.forename: Ali A
authors.initials: AA
authors.lastname: Hussain
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Jackson
authors.forename: Joanna R
authors.initials: JR
authors.lastname: Cunningham
authors.forename: John
authors.initials: J
authors.lastname: Marshall
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism; D001667:Binding, Competitive; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D016022:Case-Control Studies; D002829:Choroid / Q000378:metabolism*; D005134:Eye Neoplasms / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008545:Melanoma / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000493:pharmacokinetics*; D026901:Membrane Transport Proteins / Q000493:pharmacokinetics*; D008875:Middle Aged; D009994:Osmolar Concentration; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D013654:Taurine / Q000493:pharmacokinetics*; D013997:Time Factors; D000099247:Taurine Transporters
chemical_list: D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D013654:Taurine; D000099247:Taurine Transporters