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: (I) control; (2) IPC of 2 X 5 min each of preceding global ischemia (3,4,5) 0.2 mumol/l cyclosporin A (CsA, which inhibits MPTP opening), 5 mumol/l FK506 (which inhibits the phosphatase calcineurin without inhibiting MPTP opening), or 20 mumol/l atractyloside (Atr, a MPTP opener) given at reperfusion;, (6,7) pre-treatment with 30 mumol/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 infaret 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 mumol/l) was shown to reduce calcium-induced MPTP opening by 52.5 +/- 8.0% in calcein-loaded mitochondria. 5-Hydroxydecanoic acid (100 mumol/l) was able to abolish the cardio-protective effects of both diazoxide and IPC. Conclusion: One interpretation of these data is that IPC and mitochondrial K-ATP. channel activation may protect the myocardium by inhibiting MPTP opening at reperfusion. (C) 2002 Published by Elsevier Science B.V.