title: Inorganic phosphate uptake in Trypanosoma cruzi is coupled to K(+) cycling and to active Na(+) extrusion.
abstract: BACKGROUND
  Orthophosphate (Pi) is a central compound in the metabolism of all organisms, including parasites. There are no reports regarding the mechanisms of Pi acquisition by Trypanosoma cruzi.
  
  
  METHODS
  (32)Pi influx was measured in T. cruzi epimastigotes. The expression of Pi transporter genes and the coupling of the uptake to Na(+), H(+) and K(+) fluxes were also investigated. The transport capacities of different evolutive forms were compared.
  
  
  RESULTS
  Epimastigotes grew significantly more slowly in 2mM than in 50mM Pi. Influx of Pi into parasites grown under low Pi conditions took place in the absence and presence of Na(+). We found that the parasites express TcPho84, a H(+):Pi-symporter, and TcPho89, a Na(+):Pi-symporter. Both Pi influx mechanisms showed Michaelis-Menten kinetics, with a one-order of magnitude higher affinity for the Na(+)-dependent system. Collapsing the membrane potential with carbonylcyanide-p-trifluoromethoxyphenylhydrazone strongly impaired the influx of Pi. Valinomycin (K(+) ionophore) or SCH28028 (inhibitor of (H(+)+K(+))ATPase) significantly inhibited Pi uptake, indicating that an inwardly-directed H(+) gradient energizes uphill Pi entry and that K(+) recycling plays a key role in Pi influx. Furosemide, an inhibitor of the ouabain-insensitive Na(+)-ATPase, decreased only the Na(+)-dependent Pi uptake, indicating that this Na(+) pump generates the Na(+) gradient utilized by the symporter. Trypomastigote forms take up Pi inefficiently.
  
  
  CONCLUSIONS
  Pi starvation stimulates membrane potential-sensitive Pi uptake through different pathways coupled to Na(+) or H(+)/K(+) fluxes.
  
  
  CONCLUSIONS
  This study unravels the mechanisms of Pi acquisition by T. cruzi, a key process in epimastigote development and differentiation to trypomastigote forms.
authors: Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
authors: C F
authors: CF
authors: Dick
authors: A L A
authors: AL
authors: Dos-Santos
authors: D
authors: D
authors: Majerowicz
authors: L S
authors: LS
authors: Paes
authors: N L
authors: NL
authors: Giarola
authors: K C
authors: KC
authors: Gondim
authors: A
authors: A
authors: Vieyra
authors: J R
authors: JR
authors: Meyer-Fernandes
mesh_terms: D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014349:Trypanosoma cruzi / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D007093:Imidazoles; D010710:Phosphates; C035235:Sch 28080; D014634:Valinomycin; D012964:Sodium; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium