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To examine whether cardioprotection initiated by reactive oxygen species (ROS) is dependent on protein kinase C[epsilon] (PKC[epsilon]), isolated buffer-perfused mouse hearts were randomized to four groups: 1) antimycin A (AA) (0.1 [micro]g/ml) for 3 min followed by 10 min washout and then 30 rain global ischemia (I) and 2 h reperfusion (R); 2) controls of I/R alone; 3) AA bracketed with 13 min of N-2-mercaptopropionylglycine (MPG) followed by I/R; and 4) MPG (200 [micro]M) alone, followed by I/R. Isolated adult rat ventricular myocytes (ARVM) were exposed to AA (0.1 [micro]g/ml), and lucigenin was used to measure ROS production. Murine hearts and ARVM were exposed to AA (0.1 [micro]g/ml) with or without MPG, and PKC[epsilon] translocation was measured by cell fractionation and subsequent Western blot analysis. Finally, the dependence of AA protection on PKC[epsilon] was determined by the use of knockout mice (-/-) lacking PKC[epsilon]. AA exposure caused ROS production, which was abolished by the mitochondrial uncoupler mesoxalonitrile 4-trifluoromethoxyphenylhydrazone. In addition, AA significantly reduced the percent infarction-left ventricular volume compared with control I/R (26 [+ or -] 4 vs. 43 [+ or -] 2%; P < 0.05). Bracketing AA with MPG caused a loss of protection (52 [+ or -] 7 vs. 26 [+ or -] 4%; P < 0.05). AA caused PKC[epsilon] translocation only in the absence of MPG, and protection was lost on the pkc[[epsilon].sup.-/-] background (38 [+ or -] 3 vs. 15 [+ or -] 4%; P < 0.001). AA causes ROS production, on which protection and PKC[epsilon] translocation depend. In addition, protection is absent in PKC[epsilon] null hearts. Our results imply that, in common with ischemic preconditioning, PKC[epsilon] is crucial to ROS-mediated protection. protein kinase C; ischemic preconditioning

Objective: The basal activity of p38 MAPK has recently been shown to impair myocardial contractility. This kinase is activated by ischemia and short-term hibernation. We hypothesized that p38 MAPK activation may contribute to the contractile deficit that characterizes low-flow ischemia. Methods: In Langendorff-perfused isolated C57BL/6 mouse hearts, perfusion pressure was reduced from 85 to 15 or 30 mm Hg for 120 min to induce ischemic left ventricular dysfunction. The effect of the p38 MAPK inhibitor SB203580 (1 μM/l) on contractile function and p38 MAPK activation was assessed. Results: Reduction in perfusion pressure to 15 or 30 mm Hg was accompanied by stable reductions in coronary flow (83±2% and 66±2%, respectively) and developed pressure (84±2% and 61±3%), with minimal infarction (15.6±0.69% and 10.6±0.98% of LV myocardium, respectively), but marked activation of p38 MAPK (reflected in pHSP27 1092±326% basal and 996±301% basal, respectively). The p38 MAPK inhibitor SB203580, present during the last 60 min of reduced pressure perfusion, prevented p38 MAPK activation (pHSP27 281±92% basal, p=0.01 and 186±72% basal, p=0.01) but, despite the presence of a contractile reserve, had no effect on developed pressure. Similarly, early treatment with SB203580 started 5 min after the onset of reduced flow also failed to attenuate contractile dysfunction. Conclusion: The p38 MAPK activation that accompanies short-term hibernation does not appear to contribute to the contractile deficit. [Copyright &y& Elsevier]