Inhibiting mitochondrial permeability transition pore opening: a new paradigm for myocardial preconditioning?
OBJECTIVE
We propose that ischemic preconditioning (IPC) and mitochondrial K(ATP) channel activation protect the myocardium by inhibiting mitochondrial permeability transition pore (MPTP) opening at reperfusion.


METHODS
Isolated rat hearts were subjected to 35 min ischemia/120 min reperfusion and assigned to the following groups: (1) control; (2) IPC of 2x5 min each of preceding global ischemia; (3,4,5) 0.2 micromol/l cyclosporin A (CsA, which inhibits MPTP opening), 5 micromol/l FK506 (which inhibits the phosphatase calcineurin without inhibiting MPTP opening), or 20 micromol/l atractyloside (Atr, a MPTP opener) given at reperfusion; (6,7) pre-treatment with 30 micromol/l diazoxide (Diaz, a mitochondrial K(ATP) channel opener) or 200 nmol/l 2 chloro-N(6)-cyclopentyl-adenosine (CCPA, an adenosine A1 receptor agonist); (8) IPC+Atr; (9) Diaz+Atr; (10) CCPA+Atr. The effect of mitochondrial K(ATP) channel activation on calcium-induced MPTP opening in isolated calcein-loaded mitochondria was also assessed.


RESULTS
IPC, CsA when given at reperfusion, and pre-treatment with diazoxide or CCPA all limited infarct size (19.9+/-2.6% in IPC; 24.6+/-1.9% in CsA, 18.0+/-1.7% in Diaz, 20.4+/-3.3% in CCPA vs. 44.7+/-2.0% in control, P<0.0001). Opening the MPTP with atractyloside at reperfusion abolished this cardio-protective effect (47.7+/-1.8% in IPC+Atr, 42.3+/-3.2% in Diaz+Atr, 51.2+/-1.6% in CCPA+Atr). Atractyloside and FK506, given at reperfusion, did not influence infarct size (45.7+/-2.1% in Atr and 43.1+/-3.6% in FK506 vs. 44.7+/-2.0% in control, P=NS). Diazoxide (30 micromol/l) was shown to reduce calcium-induced MPTP opening by 52.5+/-8.0% in calcein-loaded mitochondria. 5-Hydroxydecanoic acid (100 micromol/l) was able to abolish the cardio-protective effects of both diazoxide and IPC.


CONCLUSIONS
One interpretation of these data is that IPC and mitochondrial K(ATP) channel activation may protect the myocardium by inhibiting MPTP opening at reperfusion.
Hausenloy
Derek J
DJ
The Hatter Institute for Cardiovascular Studies, Center for Cardiology, University College London Hospitals and Medical School, Grafton Way, UK.
Maddock
Helen L
HL
Baxter
Gary F
GF
Yellon
Derek M
DM
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001278:Atractyloside / Q000494:pharmacology; D065095:Calcineurin Inhibitors; D016572:Cyclosporine / Q000494:pharmacology*; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006880:Hydroxy Acids / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects*; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D017202:Myocardial Ischemia / Q000378:metabolism*; D015428:Myocardial Reperfusion Injury / Q000378:metabolism; D010477:Perfusion; D010539:Permeability; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism; D058906:Purinergic P1 Receptor Agonists; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D016559:Tacrolimus / Q000494:pharmacology
D065095:Calcineurin Inhibitors; D003652:Decanoic Acids; D004791:Enzyme Inhibitors; D006880:Hydroxy Acids; D007473:Ion Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D058906:Purinergic P1 Receptor Agonists; D001278:Atractyloside; C058394:2-chloro-N(6)cyclopentyladenosine; C052853:5-hydroxydecanoic acid; D016572:Cyclosporine; D000241:Adenosine; D003981:Diazoxide; D016559:Tacrolimus