Ischemic preconditioning (PC) has been shown to attenuate intracellular acidification during a subsequent period of
ischemia, to minimize stunning, and to decrease
infarct size, PKC activation has been suggested to be involved in this phenomenon. The present study is designed to test whether PKC activation could mimic and PKC inhibition could block the PC effects on intracellular acidification during
ischemia and on stunning during reflow in Langendorff perfused rat hearts. Prior to 20 min of sustained global normothermic
ischemia, groups of hearts were treated with the PKC activators 4
beta-phorbol 12-myristate 13-acetate (PMA) or 1,2-dioctanoyl-srt-glycerol (DOG), a group of hearts was treated with the PKC inhibitor
chelerythrine (CH), a group was treated with DOG plus CH, a group was preconditioned with four cycles of 5 min of
ischemia and 5 min of reflow, and a group was treated with CH during PC. Recovery of left ventricular developed pressure (% of initial, pretreatment, preischemic LVDP), measured after 20 min of reflow, was improved in hearts treated with DOG, but not PMA (80 +/- 3% (DOG), 55 +/- 3% (PMA) v 51 +/- 3% (control), P < 0.05 between DOG and control), although both caused a similar degree of PKC translocation (measured by fractionation followed by an assay of PKC activity using incorporation of 32P into
histone). The improved recovery of LVDP in the PC group and in the DOG group was blocked by
chelerythrine. Measurement of pH (by 31P NMR) showed that DOG reduced acidification at 15-20 min of
ischemia, although the effect was not as great as PC, while PMA did not reduce acidification. The effect of DOG on pHi was attenuated by CH; however, the PC-induced attenuation of the fall in pHi, was not affected by CH. High energy
phosphates (measured by 31P NMR) were not significantly different between any of the groups during
ischemia or reflow. This study confirms that the protective effect of ischemic preconditioning on stunning in rat heart can be eliminated by inhibition of PKC, but suggests that the effect of PC on the fall in pHi during sustained
ischemia is not mediated by PKC.