Mitochondrial uncoupling, with low concentration FCCP, induces ROS-dependent cardioprotection independent of KATP channel activation.
OBJECTIVE
Both K(ATP) channel opening drugs and ischaemic preconditioning have been suggested to protect the ischaemic heart by acting on K(ATP) channels in the inner mitochondrial membrane, uncoupling the proton gradient and partially dissipating the mitochondrial membrane potential. The aim of these studies was to use low concentrations of FCCP, a mitochondrial protonophore, to bypass the mitochondrial K(ATP) channel and partially uncouple the mitochondria and establish whether this activates protective pathways within the rat heart analogous to K(ATP) channel openers or preconditioning.


METHODS
Isolated, Langendorff-perfused rat hearts were subjected to 25 min global zero-flow ischaemia and functional recovery assessed. Hearts were pretreated with FCCP (30-300 nM) in the presence or absence of glibenclamide (1 microM), 5-hydroxydecanoate (5-HD: 100 microM), N-acetyl cysteine (4 mM), or N-2-mercaptopropionyl glycine (1 mM). The metabolic consequences of FCCP perfusion in isolated hearts were studied using (31)P NMR, and reactive oxygen species (ROS) production was measured using DCF fluorescence in isolated rat ventricular myocytes.


RESULTS
FCCP exerted a dose-dependent cardioprotective effect, with 100 nM FCCP being the optimal concentration. This effect could not be blocked by glibenclamide or 5-HD, but was completely attenuated by N-acetyl cysteine and N-2-mercaptopropionyl glycine. Perfusion with FCCP (100 nM) did not deplete bulk ATP during the pretreatment period but significantly depleted phosphocreatine. In ventricular myocytes, FCCP caused an antioxidant-sensitive increase in ROS production but diazoxide was without effect.


CONCLUSIONS
In the isolated rat heart, partial mitochondrial uncoupling with low-dose FCCP significantly improves post-ischaemic functional recovery via a ROS-dependent pathway. This cardioprotection is not mediated via the depletion of cellular ATP or mitochondrial K(ATP) channel activation.
Brennan
Jonathan P
JP
Cardiac Physiology (Cardiovascular Division), The Rayne Institute, St Thomas' Hospital, King's College London, SE1 7EH, UK.
Southworth
Richard
R
Medina
Rodolfo A
RA
Davidson
Sean M
SM
Duchen
Michael R
MR
Shattock
Michael J
MJ
D000111:Acetylcysteine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology*; D003652:Decanoic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016166:Free Radical Scavengers / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006880:Hydroxy Acids / Q000494:pharmacology; D019157:Ischemic Preconditioning, Myocardial; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008856:Microscopy, Fluorescence; D008929:Mitochondria, Heart / Q000378:metabolism*; D017202:Myocardial Ischemia / Q000378:metabolism*; D010477:Perfusion; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000032:analysis / Q000378:metabolism*; D008625:Tiopronin / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology*
D000889:Anti-Arrhythmia Agents; D003652:Decanoic Acids; D016166:Free Radical Scavengers; D006880:Hydroxy Acids; D015221:Potassium Channels; D017382:Reactive Oxygen Species; D014475:Uncoupling Agents; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; C052853:5-hydroxydecanoic acid; D000255:Adenosine Triphosphate; D008625:Tiopronin; D005905:Glyburide; D000111:Acetylcysteine