Fig. 1.

MnSOD activity in WI-38 cultures exposed to different oxygen tensions for various periods of time. Mitotically active cultures were grown 3 days at under an ambient oxygen tension of 38 mm Hg then refed and transferred to the different oxygen tensions for 24 or 48 h (24 Log and 48 Log; upper panel). Non-growing cultures were grown to saturation density under 5% oxygen, refed with medium that contained 0.5% serum, and then transferred to different oxygen tensions. The non-proliferating, confluent (C) cultures were harvested and analyzed after 24, 48, 72, 96, and 168 h (24 C, 48 C, 72 C, 96 C, and 168 C; lower panel). Senescent cultures were harvested after 48-h exposure to different oxygen tensions (see “Methods”)