Mitochondrial ATP-dependent potassium channels -: Viable candidate effectors of ischemic preconditioning

Pharmacological evidence has implicated ATP-dependent potassium (K-ATP) channels in the mechanism of ischemic preconditioning; however, the effects of sarcolemmal K-ATP channels on excitability cannot account for the protection. K-ATP channels also exist in mitochondrial inner membrane. To test whether such channels play a role in cardioprotection, we simultaneously measured flavoprotein fluorescence, an index of mitochondrial redox state, and sarcolemmal K-ATP currents in intact rabbit ventricular myocytes, Our results show that diazoxide, a K-ATP channel opener, induced reversible oxidation of flavoproteins, but did not activate sarcolemmal K-ATP channels. This effect of diazoxide was blocked by 9-hydroxydecanoic acid (5-HD), We further verified that 5-HD is a selective blocker of the mitochondrial K-ATP channels, These methods have enabled us to demonstrate that the activity of mitochondrial K-ATP channels can be regulated by protein kinase C. In a cellular model of simulated ischemia, inclusion of diazoxide decreased the rate of cell death to about half of that in control, Such protection is inhibited by 5-HD, In conclusion, our results demonstrate that diazoxide targets mitochondrial but not sarcolemmal K-ATP channels, and imply that mitochondrial K-ATP channels may mediate preconditioning.