Cardioprotective Effect of the Ischemic Preconditioning: Its Relation to Activation of Protein Kinase C

ABSTRACT

BACKGROUND: We tested recent evidences that IP triggers selective activation of protein kinase C (PKC) isozymes using isolated Langendorff-perfused rabbit heart with PKC activator, phorbol ester (PMA, 0.01 nM) or inhibitor (calphostin C, 200 nM). METHODS: After stabilization of baseline hemodynamics, the hearts were subjected to 45 min global ischemia (I) followed by 120 min reperfusion (R) with IP (IP group, n=18) or without IP (ischemic control group, n=16). IP was induced by single episode of 5 min I and 10 min R. In the PMA-treated group (n=19) and calphostin C-treated preconditioned group (n=15), PMA and calphostin C was given for 5 and 15 min before 45 min I, respectively. Myocardial cytosolic and membrane PKC activities were measured by 32P- -ATP incorporation into PKC-specific pepetide PKC isozymes were analyzed by Western blot with monoclonal antibodies. RESULTS: IP significantly increased the recovery of the LV function including LVDP and coronary flow (p <0.05)however, enhancement of the functional recovery disappeared by calphostin C or PMA treatment. Cytosolic PKC activity decreased to 82-76% in the IP and PMA-treated group (p <0.05) membrane PKC activity increased to 218-272% (p <0.01). However, both fraction of PKC activity was not changed in the calphostin C-treated preconditioned group. In addition, Western blot revealed that PKC- alpha and epsilon, especially epsilon, were selectively translocated during subsequent sustained ischemia after IP or PMA administration. IP and PMA also reduced infarct size (frim 38 to 10-20%, p <0.05). However, calphostin C blocked infarct reduction effect of IP. CONCLUSION: These results indicate that in isolated rabbit heart model, cardioprotective effect of IP may be related, at least in part, to trigger selective translocation of PKC, especially epsilon isotype.