title: Cardiac ischemia causes inhibition of the Na/K ATPase by a labile cytosolic compound whose production is linked to oxidant stress.
abstract: OBJECTIVE
  Intracellular Na rises rapidly during cardiac ischemia and this has been attributed to the combination of increased influx of Na via sodium-proton exchange and decreased activity of the Na/K ATPase. The aim of these studies was to investigate the effects of ischemia on Na/K ATPase function in Langendorff-perfused rat hearts.
  
  
  METHODS
  Na/K ATPase activity was determined by measuring ouabain-sensitive phosphate generation from ATP by cardiac homogenates.
  
  
  RESULTS
  Global ischemia (15 and 30 min) caused a substantial reduction in Na/K ATPase function despite high substrate availability in the assay. When sarcolemmal membranes were purified away from the cytosol a profound activation of the Na/K ATPase was revealed following ischemia, indicating that the inhibition was due to the cytosolic accumulation of an inhibitor of Na/K ATPase. The half-life of the inhibitor in cardiac homogenates was 10+/-3 min at room temperature. Perfusion with the antioxidant MPG (1 mmol/l) reduced the accumulation of this inhibitor, however MPG was without effect on Na/K ATPase function when added directly to the Na/K ATPase activity assay. While the inhibitor reduced the activity of cardiac and brain forms of the Na/K ATPase in bioassay experiments, no effect was observed on the renal and skeletal muscle forms of the enzyme.
  
  
  CONCLUSIONS
  An unstable cardiac and brain-specific inhibitor of the Na/K ATPase whose production is linked to oxidant stress, accumulates intracellularly during ischemia. Intracellular Na is a primary determinant of electro-mechanical recovery on reperfusion, so inhibition of the Na/K ATPase by this compound may be crucial in determining recovery from ischemia.
authors.affiliation: Cardiac Physiology, Centre for Cardiovascular Biology and Medicine, King's College London, The Rayne Institute, St. Thomas' Hospital, SE1 7EH, London, UK.
authors.forename: William
authors.initials: W
authors.lastname: Fuller
authors.forename: Vina
authors.initials: V
authors.lastname: Parmar
authors.forename: Philip
authors.initials: P
authors.lastname: Eaton
authors.forename: James R
authors.initials: JR
authors.lastname: Bell
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Shattock
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001681:Biological Assay; D001685:Biological Factors / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D017202:Myocardial Ischemia / Q000201:enzymology*; D009924:Organ Culture Techniques; D010042:Ouabain / Q000494:pharmacology; D018384:Oxidative Stress; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000201:enzymology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D001685:Biological Factors; D004791:Enzyme Inhibitors; C110658:N-(2-mercaptoproprionyl)-glycine; D013438:Sulfhydryl Compounds; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D005998:Glycine