title: Phorbol esters augment polyamine transport by influencing Na(+)-K+ pump in murine leukemia cells.
abstract: In this report, we elucidate the role of Na(+)-K+ pump in the regulation of polyamine spermidine (Spd) transport in murine leukemia (L 1210) cells in culture. Ouabain, known to bind extracellularly to the alpha-subunit of the Na(+)-K+ pump, inhibits the pump activity. The L 1210 cells were found to possess ouabain binding sites at 7.5 fmol/10(6) cells. Ouabain significantly inhibited the Spd uptake in a dose-dependent manner. The maximum inhibition of Spd uptake by ouabain was observed beyond 200 microM. Spd transport was inversely correlated with the [3H]ouabain binding to L 1210 cells: an increase in the saturation of ouabain binding to L 1210 cells resulted in a decrease of the Spd uptake process. Treatment of L 1210 cells with protein kinase C activator phorbol esters increased the Spd transport and, also, ouabain-sensitive 86Rb+ uptake, a measure of the activity of the Na(+)-K+ pump. H-7, a protein kinase C inhibitor, significantly inhibited the ouabain-sensitive 86Rb+ uptake by L 1210 cells. Phorbol esters stimulated the level, but not the rate, of 22Na+ influx. Addition of H-7 to L 1210 cells inhibited the 22Na+ influx process. A concomitant phorbol ester-induced increase in 22Na+ influx, [14C]Spd uptake, together with the functioning of Na(+)-K+ pump, indicates the role of the "Na+ cycle" in the regulation of the polyamine transport process.
authors.affiliation: Unité Fonctionnelle de Biologie Cellulaire, Centre Hospitalier Universitaire de Rennes, Faculté de Médecine, France.
authors.forename: N A
authors.initials: NA
authors.lastname: Khan
authors.forename: V
authors.initials: V
authors.lastname: Quemener
authors.forename: J P
authors.initials: JP
authors.lastname: Moulinoux
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D007546:Isoquinolines / Q000494:pharmacology; D007939:Leukemia L1210 / Q000378:metabolism*; D051379:Mice; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011073:Polyamines / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D007546:Isoquinolines; D010879:Piperazines; D011073:Polyamines; D010042:Ouabain; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D012964:Sodium; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D013755:Tetradecanoylphorbol Acetate