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.
Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Y
Y
Liu
T
T
Sato
J
J
Seharaseyon
A
A
Szewczyk
B
B
O'Rourke
E
E
Marbán
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