[Study on changes of calpain and myocardial damage in rats with burn-blast combined injury]

Objective: To study myocardial damage and rules of calpain change in rats with burn-blast combined injury. Methods: One hundred and twenty-eight male SD rats were randomly divided into control group, burn group, blast group, burn-blast group, with 32 rats in each group.

37 degrees' warm water for 12 s; Burn group: 94 degrees' boiling water for 12 s; Blast group: 5 g cyclonite explode in 75 cm distance from left chest wall of rat; Burn-blast group: burn group and blast group combined modeling method. At 6, 24, 48, 72 h observation points after injury, abdominal aorta blood samples and myocardial specimen were collected. Left ventricular ejection fraction (EF), left ventricular fractional shortening index (FS) were measured through color Doppler ultrasound instrument; Myocardial tissue was stained with hematoxylin-eosin (HE); serum cardiac troponin I (CTnI) and creatine kinase isoenzyme (CK-MB) were detected; detection of cell apoptosis in myocardial tissue was performed by terminal deoxynucleotidyl transferase-mediated dUTP notch labeling technique (Tunel). Expression levels of calpain mRNA level and protein were detected with Real-time fluorescent quantitative polymerase chain reaction (RT-PCR) and Western imprinting method analysis; calpain activity was detected by fluorescence spectrophotometry. Results: The injury of burn-blast combined injured rats was obvious, including myocardial interstitial edema, large area of myocardial cell degeneration and disintegration and the number of neutrophil infiltration increased. Cardiac function decreased 24 h after injury in burn group, blast group, burn-blast group; both EF and FS were significant lower than those of control group (all P<0.05). FS at 48, 72 h and EF at 72 h in burn-blast group were significantly lower than those of burn group, blast group at the same time points (all P<0.05); the level of cTnI in burn-blast group rose and was higher than control group at all time points, higher than the burn group, blast group at 48 h (all P<0.05). CK-MB in burn-blast group rats increased after injury, lowered at 24 h and rose again at 48 h. The level was significantly higher than control group and burn group (both P<0.05). Comparing to control group, myocardial apoptosis index in burn group, blast group and burn-blast group were significantly increased (all P<0.05). Those of burn group (25.3±4.0) at 24 h and (28.8±5.3) at 48 h were significantly lowered than burn-blast group (43.3±9.4), (53.3±10.4) at same time points, and burn group (31.9±6.7) at 72 h was significantly higher than blast group (17.3±6.3) (all P<0.05). Compared to control group, Calpain mRNA and protein expression in myocardial tissue were significantly increased in burn-blast group at all time points (all P<0.05). Calpain activity reached the peak at 24 h after injury, then gradually declined, and was significantly higher than control group (all P<0.05). Conclusion: Calpain expression and activity increase in burn-blast combined injured rats which leads to myocardial damage.