Protein kinase C isoform-dependent myocardial protection by ischemic preconditioning and potassium cardioplegia

Abstract

Objective: Ischemic preconditioning combined with potassium cardioplegia does not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium cardioplegia is dependent on protein kinase C isoform. Methods: Isolated and crystalloid-perfused rat hearts underwent 5 cycles of 1 minute of ischemia and 5 minutes of reperfusion (low-grade ischemic preconditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion (high-grade ischemic preconditioning) or time-matched continuous perfusion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective protein kinase C inhibitor chelerythrine (5 μmol/L) was administered throughout the preischemic period. All hearts underwent 35 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Isovolumic left ventricular function and creatine kinase release were measured as the end points of myocardial protection. Distribution of protein kinase C α, δ and ε in the cytosol and the membrane fractions were analyzed by Western blotting and quantified by a densitometric assay. Results: Low-grade ischemic preconditioning was almost as beneficial as potassium cardioplegia in improving functional recovery; left ventricular developed pressure 30 minutes after reperfusion was 70 ± 15 mm Hg (P < .01) in low-grade ischemic preconditioning and 77 ± 14 mm Hg (P < .05). Chelerythrine itself had no significant effect on functional recovery and creatine kinase release in the control hearts, but it did inhibit the salutary effects not only of low-grade and high-grade ischemic preconditioning but also those of potassium cardioplegia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C α to the membrane, whereas high-grade ischemic preconditioning also enhanced translocation of protein kinase C δ and ε. Chelerythrine inhibited translocation of all 3 protein kinase C isoforms. Conclusions: These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through enhanced translocation of protein kinase C α to the membrane. It is therefore suggested that activation of the novel protein kinase C isoforms is necessary to potentiate myocardial protection under potassium cardioplegia.