title: Comparison of nucleoside transport binding sites in rabbit iris-ciliary body and cultured rabbit nonpigmented ciliary epithelial cells.
abstract: The iris-ciliary body (ICB) is a site of action for topically applied antiglaucoma drugs. Moreover, adenosine has been implicated as a modulator of aqueous humor dynamics. The present study compares the binding of the nucleoside transporter probe, [3H]nitrobenzylthioinosine ([3H]NBMPR), to homogenates prepared from rabbit ICB and a cultured rabbit nonpigmented ciliary epithelial cell line (NPE) to determine whether NPE can be used as an experimental model to study the nucleoside transporter. Linear transformation of the saturation binding data revealed that [3H]NBMPR binds to a homogeneous population of binding sites with similar binding affinities (Kd = 0.3 +/- 0.1 and 0.6 +/- 0.1 nM in NPE and ICB, respectively). However, the maximal binding capacity in NPE (Bmax = 288 +/- 54 fmol/mg protein) was significantly higher than that in ICB (Bmax = 154 +/- 17 fmol/mg protein). Selected inhibitors of the nucleoside transport system and structural analogs of adenosine inhibited the binding in both homogenate preparations with a similar rank order of potency: NBMPR > DPY > CV-1808 > CHA > R-PIA > S-PIA > 2-CADO > NECA. The results suggest that NPE is a useful model which could be used for characterizing the nucleoside transporter in ICB and for the screening of nucleoside transport inhibitors as potential antiglaucoma drugs.
authors.affiliation: Department of Pharmacology and Toxicology, Morehouse School of Medicine, Atlanta, Georgia, USA.
authors.forename: E F
authors.initials: EF
authors.lastname: Williams
authors.forename: T C
authors.initials: TC
authors.lastname: Chu
authors.forename: R R
authors.initials: RR
authors.lastname: Socci
authors.forename: L G
authors.initials: LG
authors.lastname: Brown
authors.forename: C E
authors.initials: CE
authors.lastname: Walker
authors.forename: E L
authors.initials: EL
authors.lastname: Manor
mesh_terms: D000241:Adenosine / Q000819:agonists / Q000378:metabolism; D000345:Affinity Labels / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001798:Blood Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D002924:Ciliary Body / Q000166:cytology / Q000378:metabolism*; D004176:Dipyridamole / Q000378:metabolism / Q000494:pharmacology; D004848:Epithelium / Q000378:metabolism; D005260:Female; D007498:Iris / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D033703:Nucleoside Transport Proteins; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits; D013868:Thioinosine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000345:Affinity Labels; D001798:Blood Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D013868:Thioinosine; D004176:Dipyridamole; C001789:4-nitrobenzylthioinosine; D000241:Adenosine