Src tyrosine kinase is the trigger but not the mediator of ischemic preconditioning

The signal cascade that triggers and mediates ischemic preconditioning (IPC ) remains unclear. The present study investigated the role of the Sm family of tyrosine kinases in IPC. Isolated and buffer-perfused rat hearts underw ent IPC with three cycles of 5-min ischemia and 5-min reperfusion, followed by 30-min ischemia and 120-min reperfusion. The Src tyrosine kinase family -selective inhibitor PPI was administered between 45 and 30 min before isch emia (early PP1 treatment) or for 15 min before IPC [early PP1-precondition ing (PC) treatment]. PPI was also administered for 5 min before the sustain ed ischemia (late PP1 treatment) or after IPC (late PP1-PC treatment). Src kinase was activated after 30 min of ischemia in both the membrane and cyto solic fractions. Src kinase was also activated by IPC but was attenuated af ter the sustained ischemia. Early and late PP1 treatment inhibited Src acti vation after the sustained ischemia and reduced infarct size. Early PPI-PC inhibited Src activation after IPC but not after the sustained ischemia and blocked cardioprotection afforded by IPC. Late PP1-PC treatment abrogated IPC-induced activation of Src and protein kinase C (PKC)-epsilon in the mem brane but not in the cytosolic fraction. This treatment modality abrogated Src activation after the sustained ischemia and failed to block cardioprote ction afforded by IPC. These results suggest that Src kinase activation med iates ischemia injury but triggers IPC in the position either upstream of o r parallel to membrane-associated PKC-epsilon.