Postconditioning via stuttering reperfusion limits myocardial infarct size in rabbit hearts: role of ERK1/2

Abstract

Emerging evidence suggests that restoration of blood flow in a stuttering manner may limit lethal myocardial ischemia-reperfusion injury. However, the mechanisms contributing to this phenomenon, termed postconditioning (post-C), remain poorly defined. Our aim was to test the hypothesis that activation of classic “survival kinases,” phosphatidylinositol 3-kinase (PI3-kinase) and/or extracellular signal-regulated kinase (ERK)1/2, may play a role in post-C-induced cardioprotection. In protocol 1 , isolated buffer-perfused rabbit hearts underwent 30 min of sustained coronary artery occlusion and were randomized to receive abrupt reperfusion (controls) or four cycles of 30 s of reperfusion and 30 s of reocclusion before full restoration of flow (post-C). Protocol 2 was identical except control and postconditioned hearts received the PI3-kinase inhibitor LY-294002 ( protocol 2A ) or the ERK1/2 antagonist PD-98059 ( protocol 2B ) throughout the first 25 min of reperfusion, whereas in protocol 3 , myocardial samples were obtained during the early minutes of reflow from additional control, postconditioned, and nonischemic sham hearts for the assessment, by standard immunoblotting, of phospho-Akt (downstream target of PI3-kinase) and phospho-ERK. Protocols 1 and 2 corroborated that infarct size (delineated by tetrazolium staining and expressed as a percent of risk region) was reduced in postconditioned hearts vs. control hearts and also revealed that post-C-induced cardioprotection was maintained despite LY-294002 treatment but was abrogated by PD-98059. These pharmacological data were supported by protocol 3 , which showed increased immunoreactivity of phospho-ERK but not phospho-Akt with post-C. Thus our results implicate the involvement of ERK1/2 rather than PI3-kinase/Akt in the reduction of infarct size achieved with post-C.