OBJECTIVECalcium plays an important role in the impairment of heart function and arrhythmia under the condition of acute hypoxia, but the mechanism is different from that of chronic hypoxia. This study aimed to evaluate the effect of chronic hypoxia on the expression of calmodulin (CaM) and calcicum/calmodulin-dependent protein kinase II (CaMKII) and the calcium activity in myocardial cells through an animal model of chronic hypoxia in order to get a deeper sight into the mechanism.

METHODSA chronic hypoxia model of the rat was prepared by hypoxia exposure (FiO2=10%). The expression of mRNA and protein of CaM and CaMKIIgamma and CaMKIIdelta in myocardial cells were measured by RT-PCR and Western Blot in normal rats and hypoxia rats 1 and the 3 weeks after exposure. The cardiac cells of the rats from the control group and the 3-week hypoxia group were cultured. Then the intracellular calcium activity was detected using laser confocal equipment. The effect of CaMKII on the calcium activity in myocardial cells was evaluated by the application of KN-62 (CaMKII specific inhibitor).

RESULTSThe expression of CaM, CaMKIIgamma and CaMKIIdelta mRNA in myocardial tissues increased in hypoxia rats compared with that in normal controls (P<0.01). The CaM and CaMKIIdelta mRNA expression was different between the 1-week and the 3-week hypoxia groups (P<0.01). The laser confocal demonstrated that the amplitude of calcium wave in hypoxic myocardial cells was not different from that in normal controls, but the duration of calcium wave in hypoxic myocardial cells was longer than that in normal controls (P<0.01). After KN-62 use, the amplitude of calcium wave decreased and the duration of calcium wave prolonged significantly.

CONCLUSIONSThe contents of CaM and CaMKII in myocardial cells increased under condition of chronic hypoxia as a compensation to keep calcium homeostasis in a certain time. With more prolonged hypoxia time, abnormal electric activities of heart occurred and the heart function may be impaired.