OXYGEN-SENSITIVE STAGES OF CELL-CYCLE OF HUMAN DIPLOID CELLS

The authors had established that growth of human diploid WI-38 cells is reversibly inhibited by elevated partial pressures of oxygen (P(o2)) and we were interested in determining where in the cell cycle growth was delayed. A technique combining cytospectrophotometry and autoradiography was used to determine cell cycle parameters. Confluent cells that were subcultivated and exposed to a P(o2) of 365 ± 8 mm Hg were delayed primarily after DNA synthesis but before metaphase. At a P(o2) of 590 ± 35 mm Hg, most cells did not initiate DNA synthesis, and the few that did, failed to complete the process. When exponentially growing cells that had already begun DNA synthesis were exposed to a P(o2) of 590 ± 35 mm Hg, they accumulated after completing DNA synthesis but before initiating mitosis. The rate at which [3H]thymidine was incorporated into DNA was inversely correlated with oxygen tension (P(o2) of 135-590 mm Hg). These results suggest that the process most sensitive to oxygen causes cells to be delayed after DNA synthesis but before metaphase. Slightly higher P(o2)'s were needed to inhibit the initiation of DNA synthesis. Further, the rate of DNA synthesis is decreased by elevated oxygen tensions.