Mitochondrial ATP-dependent potassium channels. Viable candidate effectors of ischemic preconditioning.
Pharmacological evidence has implicated ATP-dependent potassium (KATP) channels in the mechanism of ischemic preconditioning; however, the effects of sarcolemmal KATP channels on excitability cannot account for the protection. KATP 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 KATP currents in intact rabbit ventricular myocytes. Our results show that diazoxide, a KATP channel opener, induced reversible oxidation of flavoproteins, but did not activate sarcolemmal KATP channels. This effect of diazoxide was blocked by 5-hydroxydecanoic acid (5-HD). We further verified that 5-HD is a selective blocker of the mitochondrial KATP channels. These methods have enabled us to demonstrate that the activity of mitochondrial KATP 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 KATP channels, and imply that mitochondrial KATP channels may mediate preconditioning.
Liu
Y
Y
Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Sato
T
T
Seharaseyon
J
J
Szewczyk
A
A
O'Rourke
B
B
Marbán
E
E
D000818:Animals; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D006321:Heart / Q000187:drug effects; D006880:Hydroxy Acids / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D019157:Ischemic Preconditioning, Myocardial; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D008929:Mitochondria, Heart / Q000378:metabolism*; D017202:Myocardial Ischemia / Q000473:pathology; D015221:Potassium Channels
D003652:Decanoic Acids; D006880:Hydroxy Acids; D008565:Membrane Proteins; D015221:Potassium Channels; C117780:mitochondrial K(ATP) channel; C052853:5-hydroxydecanoic acid; D003981:Diazoxide