Hypoxic injury of immature cardiac myocytes under various hypothermic conditions using an in vitro cell-culture model.

The purpose of this study was to evaluate the functional and biochemical effects in immature cardiac myocytes under hypoxic and hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days, after which 12.5 x 10(5) myocytes/flask were 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 lactate dehydrogenase (LDH) were measured in the incubation medium. The myocytes were then cultured for an additional 24 h at 37 degrees C to evaluate the recovery of the myocyte beating rate. In the 4 degrees C and 37 degrees C groups, the myocyte beating rate recovery markedly decreased 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 hypoxic incubation, at 24 h, respectively. However, in the 10 degrees C, 15 degrees C, and 25 degrees C groups, this value decreased significantly only at 24 h. In the 20 degrees C group, beating rate completely recovered 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 83.7 mIU/flask and 640.7 mIU/flask at 24 h, respectively. However, in the 25 degrees C and 37 degrees C groups, this release was significantly increased only at 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)