EFFECT OF ISCHEMIC PRECONDITIONING AND PKC ACTIVATION ON ACIDIFICATION DURING ISCHEMIA IN RAT-HEART

Ischemic preconditioning (PC) has been shown to attenuate intracellula r acidification during a subsequent period of ischemia, to minimize st unning, and to decrease infarct size. PKC activation has been suggeste d 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-sn-glycerol (DOG), a group of hearts was trea ted with the PKC inhibitor chelerythrine (CH), a group was treated wit h DOG plus CH, a group was preconditioned with four cycles of 5 min of ischemia and 5 min of renew, and a group was treated with CH during P C. Recovery of left ventricular developed pressure (% of initial, pret reatment, preischemic LVDP), measured after 20 min of reflow, was impr oved 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), altho ugh both caused a similar degree of PKC translocation (measured by fra ctionation followed by an assay of PKC activity using incorporation of P-32 into histone). The improved recovery of LVDP in the PC group and in the DOG group was blocked by chelerythrine. Measurement of pH (by P-31 NMR) showed that DOG reduced acidification at 15-20 min of ischem ia, although the effect was not as great as PC, while PMA did not redu ce acidification. The effect of DOG on pH(i) was attenuated by CH; how ever, the PC-induced attenuation of the fall in pH(i) was not affected by CH. High energy phosphates (measured by P-31 NMR) were not signifi cantly different between any of the groups during ischemia or reflow. This study confirms that the protective effect of ischemic preconditio ning on stunning in rat heart can be eliminated by inhibition of PKC, but suggests that the effect of PC on the fall in pH(i) during sustain ed ischemia is not mediated by PKC. (C) 1996 Academic Press Limited