Effect of Oxygen on Growth of Cultured Myocardial Cells

The present study was designed to explore the effects of environmental oxygen as a possible regulator of cardiac cell division and growth. Trypsindispersed heart cells from the ventricles of chick embryos 8 to 12 days old were grown in culture at 37°C in a nutrient medium (NCI) with 10% fetal calf serum. They were exposed to constant 5% CO 2 gas environments in which the percent of O 2 was varied. Net protein synthesis increased progressively as O 2 was reduced from 80% to 2 to 5%. After the first 24 hours, little further protein synthesis occurred in plates grown in 80% O 2 . The rates of cellular incorporation of 14 C-amino acids and uridine-2- 14 C increased progressively as the fraction of O 2 was reduced. In cells grown at 80% O 2 , incorporation of uridine-2- 14 C into RNA was impaired before that of 14 C-amino acid into protein. After actinomycin-D (5 µg/ml) (which quickly halted uridine incorporation into the rapidly labeled fraction of RNA), the rate of incorporation of 14 C-amino acid into protein declined exponentially. This allowed for calculation of the half-life of messenger RNA (mRNA), which was the same for cells grown at 80% O 2 as for cells grown at 20% O 2 ; increased degradation of mRNA at higher P o 2 is thus ruled out. Decreased O 2 tension results in increased rates of cell division and protein synthesis in vitro. The molecular site of action appears to be at or before RNA readout from DNA.