Infarct size reduction by cyclosporine A at reperfusion involves inhibition of the mitochondrial permeability transition pore but does not improve mitochondrial respiration

INTRODUCTION: Ischemic postconditioning (PoCo) and cyclosporine A (CysA) given prior to reperfusion reduce myocardial infarct size after ischemia/reperfusion. Ischemic postconditioning's protection is characterized by better preservation of mitochondrial respiration and calcium retention capacity. Protection by CysA is not entirely clear. Cyclosporine A inhibits not only mitochondrial permeability transition pore (mPTP) opening but also the phosphatase calcineurin. We have investigated whether CysA mediates protection not only by mPTP inhibition but also through a more upstream inhibition of calcineurin with subsequently better preserved mitochondrial respiration. MATERIAL AND METHODS: Anesthetized pigs were subjected to 90 min ischemia and 10 min reperfusion initiated with either PoCo (6 × 20 s reperfusion/re-occlusion; n = 9), CysA infusion (5 mg/kg i.v.; 5 min before reperfusion; n = 4), or immediate full reperfusion (IFR; n = 8). Mitochondria were isolated from myocardial tissue for measurement of respiration and calcium retention capacity. RESULTS: In mitochondria from ischemic/reperfused myocardium, ADP-stimulated complex I respiration was similar between CysA (116 ±11 nmol O(2)/min/mg protein) and IFR (117 ±8), but better preserved with PoCo (160 ±9; p < 0.05). Calcium retention capacity was greater with both PoCo and CysA (1096 ±45 and 1287 ±128 nmol Ca(2+)/mg protein) than with IFR (756 ±103; p < 0.05). CONCLUSIONS: Cyclosporine A's protection is not associated with improved mitochondrial respiration. Protection is unlikely related to an upstream calcineurin inhibition, but is indeed secondary to mPTP inhibition.