title: L1210/B23.1 cells express equilibrative, inhibitor-sensitive nucleoside transport activity and lack two parental nucleoside transport activities.
abstract: Cultured mouse leukemia L1210 cells express the nucleoside-specific membrane transport processes designated es, ei, and cif. The es and ei processes are equilibrative, but may be distinguished by the high sensitivity of the former to 6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine (NBMPR); the cif process is mediated by a Na+/nucleoside cotransporter of low sensitivity to NBMPR. Cells of an ei-deficient clonal line, L1210/MC5-1, were mutagenized, and clones were selected in soft agar medium that contained (i) NBMPR (an inhibitor of es processes), (ii) erythro-9-(2-hydorxy-3-nonyl)adenine (an inhibitor of adenosine deaminase), and (iii) arabinofuranosyladenine (a cytotoxic substrate for the three nucleotide transporters). The selection medium did not allow es activity and selected against cells that expressed the Na(+)-linked cif process. Cells of the L1210/B23.1 clonal isolate were deficient in cif transport activity, and inward fluxes of formycin B, a poorly metabolized analog of inosine, were virtually abolished by NBMPR in these cells. In the mutant cells, nonisotopic formycin B behaved as a countertransport substrate during influx of [3H]formycin B, and inward fluxes of the latter were competitively inhibited by purine and pyrimidine nucleosides. The transport behavior of L1210/B23.1 cells indicates that (i) the mutation/selection procedure impaired or deleted the Na(+)-linked cif process and (ii) es nucleoside transport activity is expressed in the mutant cells.
authors.affiliation: Department of Pharmacology, University of Alberta, Edmonton, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Vijayalakshmi
authors.forename: L
authors.initials: L
authors.lastname: Dagnino
authors.forename: J A
authors.initials: JA
authors.lastname: Belt
authors.forename: W P
authors.initials: WP
authors.lastname: Gati
authors.forename: C E
authors.initials: CE
authors.lastname: Cass
authors.forename: A R
authors.initials: AR
authors.lastname: Paterson
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000378:metabolism; D000241:Adenosine / Q000378:metabolism; D000818:Animals; D000998:Antiviral Agents / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002999:Clone Cells; D005573:Formycins / Q000378:metabolism; D007700:Kinetics; D007939:Leukemia L1210 / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016296:Mutagenesis; D033703:Nucleoside Transport Proteins; D009705:Nucleosides / Q000378:metabolism* / Q000494:pharmacology*; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014740:Vidarabine / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D002352:Carrier Proteins; D005573:Formycins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D009705:Nucleosides; C034561:formycin B; D013868:Thioinosine; C010192:9-(2-hydroxy-3-nonyl)adenine; D014740:Vidarabine; C001789:4-nitrobenzylthioinosine; D000225:Adenine; D000241:Adenosine; D013936:Thymidine