title: Ischemic preconditioning improves mitochondrial tolerance to experimental calcium overload.
abstract: BACKGROUND
  Ca(2+) overload leads to mitochondrial uncoupling, decreased ATP synthesis, and myocardial dysfunction. Pharmacologically opening of mitochondrial K(ATP) channels decreases mitochondrial Ca(2+) uptake, improving mitochondrial function during Ca(2+) overload. Ischemic preconditioning (IPC), by activating mitochondrial K(ATP) channels, may attenuate mitochondrial Ca(2+) overload and improve mitochondrial function during reperfusion. The purpose of these experiments was to study the effect of IPC (1) on mitochondrial function and (2) on mitochondrial tolerance to experimental Ca(2+) overload.
  
  
  METHODS
  Rat hearts (n = 6/group) were subjected to (a) 30 min of equilibration, 25 min of ischemia, and 30 min of reperfusion (Control) or (b) two 5-min episodes of ischemic preconditioning, 25 min of ischemia, and 30 min of reperfusion (IPC). Developed pressure (DP) was measured. Heart mitochondria were isolated at end-Equilibration (end-EQ) and at end-Reperfusion (end-RP). Mitochondrial respiratory function (state 2, oxygen consumption with substrate only; state 3, oxygen consumption stimulated by ADP; state 4, oxygen consumption after cessation of ADP phosphorylation; respiratory control index (RCI, state 3/state 4); rate of oxidative phosphorylation (ADP/Deltat), and ADP:O ratio) was measured with polarography using alpha-ketoglutarate as a substrate in the presence of different Ca(2+) concentrations (0 to 5 x 10(-7) M) to simulate Ca(2+) overload.
  
  
  RESULTS
  IPC improved DP at end-RP. IPC did not improve preischemic mitochondrial respiratory function or preischemic mitochondrial response to Ca(2+) loading. IPC improved state 3, ADP/Deltat, and RCI during RP. Low Ca(2+) levels (0.5 and 1 x 10(-7) M) stimulated mitochondrial function in both groups predominantly in IPC. The Control group showed evidence of mitochondrial uncoupling at lower Ca(2+) concentrations (1 x 10(-7) M). IPC preserved state 3 at high Ca(2+) concentrations.
  
  
  CONCLUSIONS
  The cardioprotective effect of IPC results, in part, from preserving mitochondrial function during reperfusion and increasing mitochondrial tolerance to Ca(2+) loading at end-RP. Activation of mitochondrial K(ATP) channels by IPC and their improvement in Ca(2+) homeostasis during RP may be the mechanism underlying this protection.
authors.affiliation: Division of Cardiothoracic Surgery, University of Maryland Medical System, Baltimore, Maryland 21201, USA. crestanello.juan@mayo.edu
authors.forename: Juan A
authors.initials: JA
authors.lastname: Crestanello
authors.forename: Nicolai M
authors.initials: NM
authors.lastname: Doliba
authors.forename: Andriy M
authors.initials: AM
authors.lastname: Babsky
authors.forename: Natalia M
authors.initials: NM
authors.lastname: Doliba
authors.forename: Koki
authors.initials: K
authors.lastname: Niibori
authors.forename: Glenn J R
authors.initials: GJ
authors.lastname: Whitman
authors.forename: Mary D
authors.initials: MD
authors.lastname: Osbakken
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000008:administration & dosage*; D019194:Ischemic Preconditioning; D007656:Ketoglutaric Acids / Q000378:metabolism; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000502:physiology*; D017202:Myocardial Ischemia / Q000378:metabolism; D015425:Myocardial Reperfusion; D010101:Oxygen Consumption; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007656:Ketoglutaric Acids; D000244:Adenosine Diphosphate; D002118:Calcium