IN-VITRO EVALUATION OF DILTIAZEM ON HYPOTHERMIC INJURY TO IMMATURE MYOCYTES

The purpose of the present study was to evaluate the functional and bi ochemical effects of diltiazem (DTZ) on cardiac myocytes incubated und er hypothermic conditions. Cardiac myocytes were isolated from neonata l rat ventricles and cultured for 4 days with MCDB 107 medium. Then, m yocytes (12.5 x 10(5) myocytes/flask) were incubated at 4-degrees-C fo r 24 hours in media with or without DTZ at concentrations of 0 M (grou p C), 10(-7) M (Group Dl), 10(-6) M (group D2), 10(-5) M (group D3), o r 10(-4) M (group D4). After 24 hours at 4-degrees-C, CPK and LDH were measured. The myocytes were then cultured for 24 hours at 37-degrees- 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 cont rol (beating rate prior to hypothermic incubation). Groups Dl 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) sh owed no beating rate recovery. Release of CPK and LDH in group C was 1 12.3 mIU/flask and 457.4 mIU/flask, respectively. Groups Dl and D2 sho wed no significant differences in both enzymes compared to group C. Ho wever, 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 pr otective effects on hypothermic injury to immature cardiac myocytes; m oreover, it accelerated cellular injury at the concentrations of 10(-5 ) and 10(-4) M both functionally and biochemically. Therefore, diltiaz em may not be suitable for cardiac preservation during the neonatal pe riod.