Age as a function of ATPase activity in cultured corneal endothelial cells

As cells grown in tissue culture age, they typically become altered when compared to their in vivo counterparts. Bovine corneal endothelial cells were grown in culture for periods up to 60 days (primary = 10 days; secondary = 50 days). The plasma membrane enzymes: Na+K+ ATPase and Mg2+ ATPase were assayed for specific activity at selected intervals throughout the growth periods. In primary cultures, it was found that Na+K+ ATPase was quite low at 5 days (0.05 units), but increased fourfold at 10 days (0.22 units). By contrast, Mg2+ ATPase changed little over the same period. Tissue cultures grown secondarily had Na+K+ ATPase activity fall 0.3 units (0.52 to 0.22) for 35 days after a single trypsinization. After five trypsinizations over a 50-day period, the activity fell 0.23 units (0.33 to 0.10). The alterations in Mg2+ ATPase activity were more complex in secondary cultures. In the instance in which a single trypsinization was used, the activity fell 0.15 units at day 20, rose 0.12 units (above the starting value) at day 25, then returned to the initial level by day 35. When multiple trypsinizations were used, the activity fell 0.06 units by day 30, then remained stable for the duration. The data may be indicative of mechanisms such as receptor alteration, feedback inhibition and genetic instability when these cells are grown in culture.