title: Delayed recovery of intracellular acidosis during reperfusion prevents calpain activation and determines protection in postconditioned myocardium.
abstract: OBJECTIVE
  Indirect data suggest that delayed recovery of intracellular pH (pHi) during reperfusion is involved in postconditioning protection, and calpain activity has been shown to be pH-dependent. We sought to characterize the effect of ischaemic postconditioning on pHi recovery during reperfusion and on calpain-dependent proteolysis, an important mechanism of myocardial reperfusion injury.
  
  
  RESULTS
  Isolated Sprague-Dawley rat hearts were submitted to 40 min of ischaemia and different reperfusion protocols of postconditioning and acidosis. pHi was monitored by (31)P-NMR spectroscopy. Myocardial cell death was determined by lactate dehydrogenase (LDH) and triphenyltetrazolium staining, and calpain activity by western blot measurement of alpha-fodrin degradation. In control hearts, pHi recovered within 1.5 +/- 0.24 min of reperfusion. Postconditioning with 6 cycles of 10 s ischaemia-reperfusion delayed pHi recovery slightly to 2.5 +/- 0.2 min and failed to prevent calpain-mediated alpha-fodrin degradation or to elicit protection. Lowering perfusion flow to 50% during reperfusion cycles or shortening the cycles (12 cycles of 5 s ischemia-reperfusion) resulted in a further delay in pHi recovery (4.1 +/- 0.2 and 3.5 +/- 0.3 min, respectively), attenuated alpha-fodrin proteolysis, improved functional recovery, and reduced LDH release (47 and 38%, respectively, P < 0.001) and infarct size (36 and 32%, respectively, P < 0.001). This cardioprotection was identical to that produced by lowering the pH of the perfusion buffer to 6.4 during the first 2 min of reperfusion or by calpain inhibition with MDL-28170.
  
  
  CONCLUSIONS
  These results provide direct evidence that postconditioning protection depends on prolongation of intracellular acidosis during reperfusion and indicate that inhibited calpain activity could contribute to this protection.
authors.affiliation: Laboratorio de Cardiología Experimental, Servicio de Cardiología, Hospital Universitari Vall d'Hebron, Passeig Vall d'Hebron, 119-129, 08035 Barcelona, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Inserte
authors.forename: Ignasi
authors.initials: I
authors.lastname: Barba
authors.forename: Víctor
authors.initials: V
authors.lastname: Hernando
authors.forename: David
authors.initials: D
authors.lastname: Garcia-Dorado
mesh_terms: D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D002154:Calpain / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D006863:Hydrogen-Ion Concentration; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D008840:Microfilament Proteins / Q000378:metabolism; D015428:Myocardial Reperfusion Injury / Q000378:metabolism* / Q000473:pathology; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013049:Spectrin
chemical_list: D002154:Calpain; D002352:Carrier Proteins; D007770:L-Lactate Dehydrogenase; D008840:Microfilament Proteins; D010725:Phosphocreatine; D013049:Spectrin