[Optimal temperature of cardiac myocytes preservation under severely hypoxic status--experimental study of the isolated cardiac myocytes].

Purpose of the present study was to evaluate functional and biochemical effects of hypoxia and hypothermia on cardiac myocytes, in order to identify the optimal temperature of cardiac myocyte preservation. Cardiac myocytes isolated from the neonatal rat ventricles (1.5 x 10(6) myocytes/culture flask) were incubated under the severely hypoxic conditions (partial pressure of oxygen was 20 mmHg) for 24 hours at 4 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, 25 degrees C, and 37 degrees C. After each hypoxic incubation, CPK and LDH were measured in the incubation media. The myocytes were then cultured for additional 24 hours at 37 degrees C to evaluate the recovery of the myocyte beating rate. In 4 degrees C and 37 degrees C groups, the myocyte beating rate recovery was markedly low as 0.0% and 34.5% of the control, compared to the beating rate pr or to hypoxia, respectively (p < 0.001). Release of CPK and LDH (mIU/flask) was significantly higher in 4 degrees C (CPK: 197.1, LDH: 1395) and 37 degrees C (CPK: 138.6, LDH: 1201) groups, respectively (p < 0.001). CPK and LDH levels did not significantly increase among four (10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C) groups. In order to further confirm the optimal temperature, hypoxic incubation time was prolonged to 48 hours in 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C groups. In 20 degrees C group, the myocyte beating rate recovery was highest to be 83.7% among the groups (p < 0.001 vs 10 degrees C, 25 degrees C, p < 0.05 vs 15 degrees C). Release of CPK, 33.1 mIU/flask, was lowest in 20 degrees C group (p < 0.001 vs 10 degrees C, p < 0.05 vs 15 degrees C). Release of LDH, 550.3 mIU/flask, was lowest in 20 degrees C group (p < 0.001 vs 10 degrees C, 25 degrees C, p < 0.05 vs 15 degrees C). Thus, cellular damage was lesser in 20 degrees C group both functionally and biochemically than the other temperature groups. These results suggested that 20 degrees C appears to be an optimal temperature for severely hypoxic preservation of the cardiac myocyte. This cell culture system may provide a useful and simple method for evaluation of the direct effects of hypoxia and hypothermia on cardiac myocytes in vitro.