Protein Tyrosine Kinase is Downstream of Protein Kinase C for Ischemic Preconditioningʹs Anti-infarct Effect in the Rabbit Heart

The present study tested the hypothesis that one or more tyrosine kinase(s) are downstream of protein kinase C (PKC) in the signal transduction pathway responsible for the cardioprotective effect of ischemic preconditioning (PC). Isolated rabbit hearts were subjected to 30 min of regional ischemia followed by 2 h of reperfusion. Infarct size was measured by triphenyltetrazolium staining and expressed as a percentage of the area at risk. Infarction in control hearts was 32.9±1.8%. Ischemic PC with 5-min ischemia/10-min reperfusion reduced infarct size to 11.5±1.5% (P<0.05). Infusion of the tyrosine kinase inhibitors, genistein (50μm) or lavendustin A (0.5μm), alone did not affect the level of infarction. When infused around the 5-min PC ischemia genistein failed to block protection (13.7±1.0%). However, when present at the onset of the 30-min ischemia both genistein and lavendustin A completely aborted protection (31.4±2.0 and 28.1±1.5%, respectively). Activation of PKC by phorbol 12-myristate 13-acetate (PMA, 0.05 nmol) was as protective is ischemic PC (14.9±3.0%;P<0.05). Similar to PC, PMA-induced protection was completely prevented by both genistein and lavendustin A. Conversely, anisomycin (50 ng/ml), an activator of MAP kinase kinases (dual tyrosine and threonine kinases), was very protective (7.5±1.6%;P<0.05) and this protection was still present when PKC was inhibited by 5μmchelerythrine(12.1±1.6%;P<0.05). In conclusion, activation of a tyrosine kinase during the long ischemia appears to be required for cardioprotection in the rabbit heart. Furthermore, the ability of tyrosine kinase inhibitors to block PMA-induced protection in conjunction with the failure of PKC inhibition to prevent anisomycin-induced protection suggests that the tyrosine kinase is downstream of PKC and that the tyrosine kinase may be a MAP kinase kinase.