title: Characterization of ecto-ATPase activity in the surface of LLC-PK1 cells and its modulation by ischemic conditions.
abstract: BACKGROUND
  The concentration of extracellular nucleotides is regulated by enzymes that have their catalytic site facing the extracellular space, the so-called ecto-enzymes.
  
  
  METHODS
  We used LLC-PK1 cells, a well-characterized porcine renal proximal tubule cell line, to biochemically characterize ecto-ATPase activity in the luminal surface. The [γ-(32)P]Pi released after reaction was measured in aliquots of the supernatant by liquid scintillation.
  
  
  RESULTS
  This activity was linear with time up to 20min of reaction and stimulated by divalent metals. The ecto-ATPase activity measured in the presence of 5mM MgCl(2) was (1) optimum at pH 8, (2) insensitive to different inhibitors of intracellular ATPases, (3) inhibited by 1mM suramin, an inhibitor of ecto-ATPases, (4) sensitive to high concentrations of sodium azide (NaN(3)) and (5) also able to hydrolyze ADP in the extracellular medium. The ATP:ADP hydrolysis ratio calculated was 4:1. The ecto-ADPase activity was also inhibited by suramin and NaN(3). The dose-response of ATP revealed a hyperbolic profile with maximal velocity of 25.2±1.2nmol Pixmg(-1)xmin(-1) and K(0.5) of 0.07±0.01mM. When cells were submitted to ischemia, the E-NTPDase activity was reduced with time, achieving 71% inhibition at 60min of ischemia.
  
  
  CONCLUSIONS
  Our results suggest that the ecto-ATPase activity of LLC-PK1 cells has the characteristics of a type 3 E-NTPDase which is inhibited by ischemia.
  
  
  CONCLUSIONS
  This could represent an important pathophysiologic mechanism that explains the increase in ATP concentration in the extracellular milieu in the proximal tubule during ischemia.
authors.affiliation: Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
authors.forename: M C
authors.initials: MC
authors.lastname: Ribeiro
authors.forename: M S
authors.initials: MS
authors.lastname: Costa-Alves
authors.forename: M
authors.initials: M
authors.lastname: Wengert
authors.forename: J R
authors.initials: JR
authors.lastname: Meyer-Fernandes
authors.forename: P
authors.initials: P
authors.lastname: Zancan
authors.forename: C
authors.initials: C
authors.lastname: Caruso-Neves
authors.forename: A A S
authors.initials: AA
authors.lastname: Pinheiro
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002478:Cells, Cultured; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007511:Ischemia / Q000503:physiopathology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D018374:LLC-PK1 Cells; D013498:Suramin / Q000494:pharmacology; D013552:Swine
chemical_list: D000970:Antineoplastic Agents; D013498:Suramin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D000251:Adenosine Triphosphatases; C027201:ectoATPase