title: Uptake of 3H-cAMP by retinal pigment epithelium isolated from bluegill sunfish (Lepomis macrochirus).
abstract: BACKGROUND
  In bluegill sunfish, the melanin-containing pigment granules of the retinal pigment epithelium undergo cyclic movements in response both to ambient lighting and circadian cues. Pigment granules aggregate into the cell body at night (in the dark), and disperse into apical processes during the day (in the light). Regulation of pigment granule aggregation in a number of fishes depends on modulating the intracellular levels of cyclic adenosine monophosphate.
  
  
  RESULTS
  Here we show isolated RPE takes up cyclic adenosine monophosphate (cAMP) in a saturable manner, exogenously applied cAMP induces pigment granule aggregation in retinal pigment epithelium isolated from bluegill, and aggregation induced in this manner is inhibited by treatment with probenecid, an organic anion transport inhibitor.
  
  
  CONCLUSIONS
  Our results raise the possibility that cAMP functions as a messenger secreted from the neural retina to signal darkness to the RPE, which takes it up. It further suggests that organic anion transport systems are the route by which cAMP crosses RPE cell membranes since probenecid inhibits extracellular cAMP from causing pigment granule aggregation.
authors.affiliation: Department of Biology, Texas State University-San Marcos, San Marcos, Texas 78666, USA. takeith2003@yahoo.com <takeith2003@yahoo.com>
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Keith
authors.forename: Varsha
authors.initials: V
authors.lastname: Radhakrishnan
authors.forename: Steve
authors.initials: S
authors.lastname: Moredock
authors.forename: Dana M
authors.initials: DM
authors.lastname: García
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000008:administration & dosage / Q000493:pharmacokinetics*; D003903:Deuterium / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D010473:Perciformes; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012168:Retinal Pigments / Q000378:metabolism*
chemical_list: D012168:Retinal Pigments; D003903:Deuterium; D000242:Cyclic AMP