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

Objective: Ischemic preconditioning combined with potassium cardioplegia do es not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium ca rdioplegia 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 prec onditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfus ion thigh-grade ischemic preconditioning) or time-matched continuous perfus ion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective pr otein kinase C inhibitor chelerythrine (5 mu mol/L) was administered throug hout the preischemic period. All hearts underwent 35 minutes of normothermi c global ischemia followed by 30 minutes of reperfusion. Isovolumic left ve ntricular function and creatine kinase release were measured as the end poi nts of myocardial protection. Distribution of protein kinase C alpha, delta , and epsilon in the cytosol and the membrane fractions were analyzed by We stern blotting and quantified by a densitometric assay. Results: Low-grade ischemic preconditioning was almost as beneficial as pot assium cardioplegia in improving functional recovery; left ventricular deve loped pressure 30 minutes after reperfusion was 70 +/- 15 mm Hg (P < .01) i n low-grade ischemic preconditioning and 77 +/- 14 mm Hg (P < .001) in pota ssium cardioplegia compared with values found in unprotected control hearts (39 +/- 12 mm Hg). Creatine kinase release during reperfusion was also equ ally inhibited by low-grade ischemic preconditioning (18.2 +/- 10.6 IU/g dr y weight, P < .05) and potassium cardioplegia (17.6 +/- 6.7 IU/g, P < .01) compared with control values. However, low-grade ischemic preconditioning i n combination with potassium cardioplegia conferred no significant addition al myocardial protection; left ventricular developed pressure was 80 +/- 17 mm Hg, and creatine kinase release was 14.8 +/- 11.0 IU/g. In contrast, hi gh-grade ischemic preconditioning with potassium cardioplegia conferred bet ter myocardial protection than potassium cardioplegia alone; left ventricul ar developed pressure was 121 +/- 16 mm Hg (P < .001), and creatine kinase release was 8.3 +/- 5.8 IU/g (P < .05). Chelerythrine itself had no signifi cant effect on functional recovery and creatine kinase release in the contr ol hearts, but it did inhibit the salutary effects not only of low-grade an d high-grade ischemic preconditioning but also those of potassium cardiople gia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C alpha to the membrane, whereas high-grad e ischemic preconditioning also enhanced translocation of protein kinase C delta and epsilon. Chelerythrine inhibited translocation of all 3 protein k inase C isoforms. Conclusions: These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through en hanced translocation of protein kinase C alpha to the membrane. It is there fore suggested that activation of the novel protein kinase C isoforms is ne cessary to potentiate myocardial protection under potassium cardioplegia.