Delayed cytoprotection (preconditioning) occurs 24h after sublethal simulated ischaemia and reperfusion (SI/R) in neonatal rat ventricular cardiomyocytes. SI/R was used to investigate the role of activation of mitogen-activated protein kinases (MAPKs), stress-activated protein kinases (SAPKs) and phosphoinositide 3-kinase-dependent protein kinase B (PKB)/Akt in cytoprotection. SI resulted in transient dual (Thr/Tyr) phosphorylation of p42/p44-MAPK and p38-MAPK, weak phosphorylation of p46/p54-SAPK, but no phosphorylation of PKB. ‘Reperfusion’ caused further transient phosphorylation of p38-MAPK, but sustained phosphorylation of p42/p44-MAPK (lasting 4h) and of Ser473 of PKB (lasting 2h). Furthermore, SI/R (24h) induced delayed protection against lethal SI, as determined by an increase in cell viability {bioreduction of MTT [3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide]} and a decrease in cell injury (release of creatine kinase). Both protection and phosphorylation of p42/p44-MAPK were blocked by the MEK-1/2 (MAPK/Erk kinase-1/2) inhibitor PD98059 (50µM) when given during SI/R, but not when given during SI alone. The p38-MAPK inhibitor SB203580 (10µM) blocked the p38-MAPK-dependent phosphorylation of activating transcription factor 2 in vitro, and the phosphoinositide 3-kinase inhibitor wortmannin (100nM) blocked PKB phosphorylation on Ser473. However, neither SB203580 nor wortmannin had any effect on delayed protection. Therefore sustained activation of p42/p44-MAPK during simulated ‘reperfusion’ following sublethal SI mediates preconditioning in cardiomyocytes independently of transient activation of p38-MAPK or sustained activation of PKB.

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