Introduction: Ischemic postconditioning (P^oCo) 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 P^oCo (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 O2/min/mg protein) and IFR (117 ±8), but better preserved with P^oCo (160 ±9; p < 0.05). Calcium retention capacity was greater with both P^oCo and CysA (1096 ±45 and 1287 ±128 nmol Ca₂₊/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.