The purpose of the present study was to evaluate the functional and biochemical effects of diltiazem (DTZ) on cardiac myocytes incubated under hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 medium. Then, myocytes (12.5×105myocytes/flask) were incubated at 4°C for 24 hours in media with or without DTZ at concentrations of 0 M (group C), 10−7M (Group D1), 10−6M (group D2), 10−5M (group D3), or 10−4M (group D4). After 24 hours at 4°C, CPK and LDH were measured. The myocytes were then cultured for 24 hours at 37°C to evaluate the recovery of the myocyte beating rate. In group C (n=7), the recovery ratio of the myocyte beating rate was 29.9 of control (beating rate prior to hypothermic incubation). Groups D1 and D2 (n=7 each) had approximately the same recovery ratios as group C (24.0 and 24.7, respectively); however, groups D3 and D4 (n=7 each) showed no beating rate recovery. Release of CPK and LDH in group C was 112.3 mIU/flask and 457.4 mIU/flask, respectively. Groups D1 and D2 showed no significant differences in both enzymes compared to group C. However, the levels of CPK were significantly higher in group D4 (203.3, p<0.05), and LDH levels were significantly higher in groups D3 and D4 (669.3, p<0.05; 883.4, p<0.02). In conclusion, DTZ showed no protective effects on hypothermic injury to immature cardiac myocytes; moreover, it accelerated cellular injury at the concentrations of 10−5and 10−4M both functionally and biochemically. Therefore, diltiazem may not be suitable for cardiac preservation during the
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