title: Movement of fluorescein and its glucuronide across retinal pigment epithelium-choroid.
abstract: OBJECTIVE
  To characterize movement of fluorescein and its glucuronide across the blood-retinal barrier.
  
  
  METHODS
  Retinal pigment epithelium (RPE)-choroid preparations from New Zealand albino rabbit were sealed in an Ussing-type chamber in a stabilized condition for 3 hr, where movement of fluorescein and fluorescein glucuronide across the RPE-choroid was studied under a short circuit condition.
  
  
  RESULTS
  The outward (vitreous-choroid) permeability to fluorescein determined at a concentration of 15 mumol/l was about 4 times greater than the inward (choroid-vitreous) permeability (P < 0.01). The outward permeability was significantly decreased by 50-65% by metabolic or competitive inhibitors (1 mumol/l ouabain, 10 mumol/l 2,4-dinitrophenol, 100 mumol/l probenecid, 30 mmol/l hippurate, or 5 mmol/l iodipamide), whereas the inward permeability was not affected by any of the above competitive inhibitors. As the fluorescein concentration was increased from 15 to 150 mumol/l, the net fluorescein movement across the tissue indicated saturation, and a Lineweaver-Burk plot gave an apparent Km of 26 mumol/l and Vmax of 1.56 nmol/hr/cm2. The outward permeability to fluorescein glucuronide determined at 15 mumol/l was about double the inward permeability (P < 0.01) and about 1/3 of the outward permeability to fluorescein (P < 0.01). The outward permeability to fluorescein glucuronide was significantly decreased by about 50% by 1 mumol/l ouabain, 10 mumol/l 2,4-dinitrophenol, or 100 mumol/l probenecid, whereas the inward permeability was not affected by 100 mumol/l probenecid.
  
  
  CONCLUSIONS
  These results suggest that the majority of the outward fluorescein movement across the tissue and part of that of fluorescein glucuronide depends on an active transport mechanism, whereas the inward movement of both fluorescein and fluorescein glucuronide occurs by a passive mechanism.
authors.affiliation: Department of Ophthalmology, University of Tokyo School of Medicine, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Koyano
authors.forename: M
authors.initials: M
authors.lastname: Araie
authors.forename: S
authors.initials: S
authors.lastname: Eguchi
mesh_terms: D019297:2,4-Dinitrophenol; D000818:Animals; D001693:Biological Transport, Active; D001813:Blood-Retinal Barrier / Q000502:physiology; D002829:Choroid / Q000378:metabolism*; D004140:Dinitrophenols / Q000494:pharmacology; D005260:Female; D019793:Fluorescein; D005452:Fluoresceins / Q000493:pharmacokinetics*; D008297:Male; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D011817:Rabbits
chemical_list: D004140:Dinitrophenols; D005452:Fluoresceins; D010042:Ouabain; C041357:fluorescein glucuronide; D019297:2,4-Dinitrophenol; D019793:Fluorescein