HYPOXIC INJURY OF IMMATURE CARDIAC MYOCYTES UNDER VARIOUS HYPOTHERMICCONDITIONS USING AN IN-VITRO CELL-CULTURE MODEL

The purpose of this study was to evaluate the functional and biochemic al effects in immature cardiac myocytes under hypoxic and hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricle s and cultured for 4 days, after which 12.5 X 10(5) myocytes/flask wer e incubated under 3% hypoxic conditions at 4 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, 25 degrees C, and 37 degrees C for 6, 12, and 24 h. After each hypoxic incubation, creatine kinase (CK) and lact ate dehydrogenase (LDH) were measured in the incubation medium. The my ocytes were then cultured for an additional 24 h at 37 degrees C to ev aluate the recovery of the myocyte beating rate. In the 4 degrees C an d 37 degrees C groups, the myocyte beating rate recovery markedly decr eased with increasing incubation times from 78.1% and 97.2% at 6 h to 0.0% and 38.4% of the control, which was the beating rate prior to hyp oxic incubation, at 24 h, respectively. However, in the 10 degrees C, 15 degrees C, and 25 degrees C groups, this value decreased significan tly only at 24 h. In the 20 degrees C group, beating rate completely r ecovered in 24 h. A marked increase was found in the release of CK and LDH in the 4 degrees C group from 28.5 mIU/flask and 232.9 mIU/flask at 6 h to and 8.7 mIU/flask and 640.7 mIU/flask at 24 h, respectively. However, in the 25 degrees C and 37 degrees C groups, this release wa s significantly increased only at 24 h. In the 15 degrees C and 20 deg rees C groups, no significant increases were observed over 24 h. Below 15 degrees C, hypothermia induced cellular damage both functionally a nd biochemically, and the greatest damage was observed at 4 degrees C. Above 25 degrees C, the damage was due to hypoxia. Thus, a temperatur e of 15 degrees C to 20 degrees C appears to be suitable for hypotherm ic preservation of immature myocardium.