title: Ischemic preconditioning results in an ATP-dependent inhibition of cytochrome C oxidase.
abstract: OBJECTIVE
  This study addresses the effect of short myocardial ischemia on inhibitory effect of ATP for mitochondrial cytochrome c oxidase (CytOx) activity in myocardium and subsequent hemodynamic alterations. The activity of CytOx is inhibited by ATP (primary substrate control). This additional mechanism was proposed to be switched off at higher mitochondrial membrane potential values in case of stress. The ATP-dependent allosteric enzyme inhibition (second respiratory control) is suggested to reduce the formation of reactive oxygen species and thus is pivotal for cytoprotection. This report addresses the possible involvement of this mechanism in case of myocardial preconditioning.
  
  
  METHODS
  Rat hearts were perfused in a Langendorff system (n = 5 each group). The first two groups underwent short recurrent ischemic periods (three times 5 min) and subsequent high or low reperfusion for 40 min. Besides four control groups, hearts were exposed to an ischemia of 15 min and high flow reperfused for 30 min, in addition. Hemodynamic data were evaluated in parallel. Mitochondria were separated for the polarographic respiration measurements in the presence of ADP or ATP, respectively. Phosphorylation patterns of the CytOx subunits were studied by immunoblotting with P-Ser, P-Thr, and P-Tyr antibodies.
  
  
  RESULTS
  Short recurrent episodes of ischemia result in an ATP-dependent inhibition of CytOx. Electrophoretic analysis and blotting techniques reveal different phosphorylation patterns of the enzyme. Frequent short-lasting ischemic impacts and subsequent increased coronary flow seem to be essential for this effect.
  
  
  CONCLUSIONS
  The procedure of preconditioning is likely to be dependent on the mechanism of ATP-dependent inhibition of CytOx activity.
authors.affiliation: Cardiovascular Research Lab, Biomedical Research Center of the Philipps-University Marburg, Marburg, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Vogt
authors.forename: Rabia
authors.initials: R
authors.lastname: Ramzan
authors.forename: Petra
authors.initials: P
authors.lastname: Weber
authors.forename: Dirk
authors.initials: D
authors.lastname: Troitzsch
authors.forename: Annika
authors.initials: A
authors.lastname: Rhiel
authors.forename: Alexander
authors.initials: A
authors.lastname: Sattler
authors.forename: Marc
authors.initials: M
authors.lastname: Irqsusi
authors.forename: Volker
authors.initials: V
authors.lastname: Ruppert
authors.forename: Rainer
authors.initials: R
authors.lastname: Moosdorf
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D003326:Coronary Circulation / Q000502:physiology; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D006439:Hemodynamics / Q000502:physiology; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D008929:Mitochondria, Heart / Q000201:enzymology; D017202:Myocardial Ischemia / Q000201:enzymology / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D009924:Organ Culture Techniques; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV