Role of mitochondrial KATP channels and protein kinase C in ischaemic preconditioning

1. Activation of mitochondrial K-ATP (mitoK(ATP)) channels and protein kinase C (PKC) has been implicated in cardioprotective mechanisms of ischaemic preconditioning (IPC). However, the exact role of these events in early IPC remains unclear. 2. Isolated and perfused rat hearts underwent IPC with three cycles of 5 min ischaemia and 5 min reperfusion. The heart was subjected to 30 min global ischaemia followed by 120 min reperfusion. Flavoprotein oxidation was monitored to assess mitoK(ATP) channel activity. Cardioprotection was evaluated by recovery of isovolumic left ventricular (LV) function and infarct size. 3. Diazoxide (50 mumol/L) increased flavoprotein oxidation and conferred cardioprotection in a manner sensitive to the selective mitoK(ATP) channel blocker 5-hydroxydecanoate (5-HD; 0.5 mmol/L). 4. Pretreatment with 0.5 mmol/L 5-HD abrogated IPC-induced flavoprotein oxidation and cardioprotection, whereas late treatment with 5-HD after IPC required a higher dose (2 mmol/L) to abolish flavoprotein oxidation and cardioprotection afforded by IPC. 5. Pretreatment with the PKC inhibitors Ro318425 (1 mumol/L) and chelerythrine (5 mumol/L) abolished IPC-induced flavoprotein oxidation and cardioprotection, whereas late treatment with Ro318425 required a higher dose (4 mumol/L) to abolish flavoprotein oxidation and cardioprotection. 6. In conclusion, these results suggest that activation of mitoK(ATP) channels is the trigger and the mediator of IPC and that PKC plays a crucial role in both phases of mitoK(ATP) channel activation, although mitoK(ATP) channels and PKC may be more activated during the mediator phase.