title: Hypoxanthine enters human vascular endothelial cells (ECV 304) via the nitrobenzylthioinosine-insensitive equilibrative nucleoside transporter.
abstract: The transport properties of the nucleobase hypoxanthine were examined in the human umbilical vein endothelial cell line ECV 304. Initial rates of hypoxanthine influx were independent of extracellular cations: replacement of Na+ with Li+, Rb+, N-methyl-D-glucamine or choline had no significant effect on hypoxanthine uptake by ECV 304 cells. Kinetic analysis demonstrated the presence of a single saturable system for the transport of hypoxanthine in ECV 304 cells with an apparent K(m) of 320 +/- 10 microM and a Vmax of 5.6 +/- 0.9 pmol/10(6) cells per s. Hypoxanthine uptake was inhibited by the nucleosides adenosine, uridine and thymidine (apparent Ki 41 +/- 6, 240 +/- 27 and 59 +/- 8 microM respectively) and the nucleoside transport inhibitors nitrobenzylthioinosine (NBMPR), dilazep and dipyridamole (apparent Ki 2.5 +/- 0.3, 11 +/- 3 and 0.16 +/- 0.006 microM respectively), whereas the nucleobases adenine, guanine and thymine had little effect (50% inhibition at > 1 mM). ECV 304 cells were also shown to transport adenosine via both the NBMPR-sensitive and -insensitive nucleoside carriers. Hypoxanthine specifically inhibited adenosine transport via the NBMPR-insensitive system in a competitive manner (apparent Ki 290 +/- 14 microM). These results indicate that hypoxanthine entry into ECV 304 endothelial cells is mediated by the NBMPR-insensitive nucleoside carrier present in these cells.
authors: Departamento de Fisiología y Biofísica, Universidad de Chile, Santiago, Chile.
authors: N
authors: N
authors: Osses
authors: J D
authors: JD
authors: Pearson
authors: D L
authors: DL
authors: Yudilevich
authors: S M
authors: SM
authors: Jarvis
mesh_terms: D000241:Adenosine / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000187:drug effects* / Q000378:metabolism; D002460:Cell Line; D004730:Endothelium, Vascular / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D019271:Hypoxanthine; D007042:Hypoxanthines / Q000378:metabolism*; D008565:Membrane Proteins / Q000187:drug effects* / Q000378:metabolism; D033703:Nucleoside Transport Proteins; D013868:Thioinosine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D007042:Hypoxanthines; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D019271:Hypoxanthine; D013868:Thioinosine; C001789:4-nitrobenzylthioinosine; D000241:Adenosine