2.2. Cardiac ischemia/reperfusion (I/R) injury model

Cardiac I/R was surgically induced as described previously [39]. In brief, male C57BL/6J mice (8–12 weeks of age, 20–25 g) received AAV9 SERCA (SERCA^AAV9 group) or control AAV9 vectors (control group). These mice were anesthetized with pentobarbital sodium (60 mg/kg) and ventilated with a rodent ventilator. The left anterior descending coronary artery was ligated with a 6–0 silk suture, and ischemic damage was confirmed by observation of the blanching of the myocardium in the affected area. After 45 min of ischemia, reperfusion was achieved in the left anterior descending coronary artery for about 4 h. Animals in the sham group underwent all surgical procedures for I/R induction except the ligation step. The I/R model and treatment were performed by a single experienced operator under blinded conditions. To induce intracellular calcium overload, a single intraperitoneal (i.p.) injection of ionomycin at 1 mg/kg was used 30 min before the I/R model. In addition, to activate MCU in SERCA^AAV9 mice, spermine i.p. treatment at 5 mg/kg was used 60 min before I/R surgery. Dead mice and mice with no decrease in heart function at baseline were excluded. Completely randomized design and blinding were adopted in the animal experiments.