PI 3-kinase regulates the mitochondrial transition pore in controlled reperfusion and postconditioning.

We investigated whether phosphatidylinositol 3-kinase (PI3K) might regulate mitochondrial permeability transition pore (mPTP) opening in hearts reperfused with either low pressure or postconditioning. Male Wistar rat hearts (n=72) were perfused according to the Langendorff technique, exposed to 30 min of ischemia, and assigned to one of the following groups: (1) reperfusion with normal pressure (NP; 100 cm H2O), (2) reperfusion with low pressure (LP; 70 cm H2O), or reperfusion with postconditioning, i.e. 3 episodes of 30 s reperfusion followed by 30 s of ischemia (PostC). Hearts received either the PI3K inhibitors wortmannin or LY294002, or vehicle at the onset of the 60 min reperfusion. Postischemic functional recovery was assessed by rate-pressure product (RPP), and irreversible injury by lactate dehydrogenase (LDH), creatine kinase (CK) and troponin I (TnI) release. Mitochondria were isolated from the reperfused myocardium, and Ca2+-induced mPTP opening was measured using a potentiometric method. Functional recovery was significantly improved in LP and PostC hearts with RPP averaging 13,880+/-810 (LP) and 17,130+/-900 mm Hgxbeats/min (PostC) versus 6450+/-500 mm Hgxbeats/min in NP hearts (p<0.01). LDH release averaged 230+/-30 and 145+/-15 IU/h/g of myocardial tissue in LP and PostC versus 340+/-10 IU/h/g in NP (p<0.05). Wortmannin and LY294002 prevented both RPP improvement and decrease in LDH, CK, and TnI release in LP and PostC groups. The Ca2+ load required to induce mPTP opening averaged 58+/-3 and 52+/-1 nmol/mg mitochondrial proteins in LP and PostC groups, respectively, versus 35+/-4 nmol/mg in the NP group (p<0.01). Wortmannin and LY294002 prevented the beneficial effect in both the LP and PostC groups. These results suggest that PI3K regulates the opening of the mitochondrial permeability transition pore in rat hearts reperfused with low pressure or postconditioning.