title: Stable intracellular acidification upon polyamine depletion induced by alpha-difluoromethylornithine or N1,N12-bis(ethyl)spermine in L1210 leukaemia cells.
abstract: Polyamines play major roles in ionic and osmotic regulation, but their exact involvement in specific ion transport processes is poorly defined. Treatment of L1210 mouse leukaemia cells with either 5 mM alpha-difluoromethylornithine (DFMO), a suicide substrate of ornithine decarboxylase, or 25 microM N1,N12-bis(ethyl)spermine (BE-3-4-3), a dysfunctional polyamine analogue, caused a stable decreased in intracellular pH (pHi) by 0.1-0.4 unit from steady-state control values between 7.4 and 7.6, as measured either by partition of a weak acid or with a fluorescent pH-sensitive probe. This effect was not related to cell growth status or differences in metabolic acid generation, and was observed in either the presence or absence of HCO3-. Exogenous spermidine (10-25 microM) or putrescine (25-50 microM) fully reversed DFMO- or BE-3-4-3-induced acidification within 2 and 8 h respectively. Recovery of pHi in L1210 cells after a nigericin- or NH4(+)-mediated acid load in HCO3(-)-free buffers was mediated by Na+/H+ antiporter activity, in addition to a minor Na(+)-independent and amiloride-insensitive pathway. Decreased steady-state pHi was maintained in polyamine-depleted L1210 cells after recovery from acid stress. Moreover, the pHi-dependence of the rate of Na(+)-dependent H+ extrusion after an acid stress was altered by DFMO and BE-3-4-3, resulting in a set-point which was lower by 0.25-0.30 pH unit in polyamine-depleted cells. On the other hand, neither the rate nor the magnitude of Na+/H(+)-exchanger-mediated alkalinization induced by hypertonic shock was decreased by polyamine depletion. Thus polyamine depletion induces a persistent defect in pHi homeostasis which is due, at least in part, to a stable decrease in the pHi set-point of the Na+/H+ exchanger.
authors.affiliation: Laboratory of Molecular Endocrinology, Laval University Medical Research Center, Ste, Foy, Que, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Poulin
authors.forename: A E
authors.initials: AE
authors.lastname: Pegg
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001639:Bicarbonates / Q000494:pharmacology; D000518:Eflornithine / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007939:Leukemia L1210 / Q000378:metabolism*; D051379:Mice; D009550:Nigericin / Q000494:pharmacology; D011073:Polyamines / Q000008:administration & dosage* / Q000494:pharmacology; D011700:Putrescine / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013095:Spermidine / Q000494:pharmacology; D013096:Spermine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D001639:Bicarbonates; D011073:Polyamines; D017923:Sodium-Hydrogen Exchangers; D013096:Spermine; C052614:N(1), N(12)-diethylspermine; D009550:Nigericin; D013095:Spermidine; D011700:Putrescine; D000518:Eflornithine