Effect of hypoxic postconditioning and diazoxide postconditioning on calreticulin expression during hypoxia/ reoxygenation in rat cardiomyocytes

Objective To investigate the effect of hypoxic postconditioning and diazoxide postconditioning on the calreticulin expression during hypoxia/reoxygenation （H/R） in rat cardiomyocytes. Methods Primary cultured male SD rat cardiomyocytes were randomly divided into 6 groups （n = 8 each）： control group （group C）,H/R group; hypoxic postconditioning group （group HP） and diazoxide postconditioning group （group DP）. Group C were cultured continuously for 2 h. Group H/R, Hp and DP were exposed to 45 min hypoxia （95% N2-5% CO2）followed by 1 h reoxygenation. In group HP, the cells were subjected to three cycles of 3 min hypoxia at 3 min intervals at the end of 45 min hypoxia before 1 h reoxygenation. In group DP, diazoxide 50 μmol/L was giyen at the end of hypoxia. Caspase-3 activity, calreticulin expression and intracellular free calcium ion concentrations were determined. Results Compared with group C, caspase-3 activity was significantly increased in the other groups,the calreticulin expression was up-regulated in group HP and DP, and the free calcium ion concentrations were increased in group H/R （P 〈 0.05 or 0.01）. Compared with group H/R, caspase-3 activity was significantly decreased in HP and DP, the calreticulin expression was up-regulated and the free calcium ion concentrations were decreased in group HP and DP （P 〈 0.01）. Conclusion Hypoxic postconditioning and diazoxide postconditioning attenuate H/R injury in rat cardiomyocytes through up-regulating the expression of calreticulin and reducing intracellular calcium overload. Key words: Anoxia; Diazoxide; Cell hypoxia; Oxygen; Calreticulin