The influence of cell population density and serum on the (Na+K)-ATPase of 3T3 cells.

The (Na+K)-ATPase of 3T3 cells has been measured as a function of culture density and the type of serum in which the cells were grown. When 3T3 cells were grown in medium containing 10% newborn calf serum their (Na+K)-ATPase activity increased as the culture density increased and the cells became quiescent at densities of about 17.5 X 10(4) cells/cm2. When these cells are subcultured into medium containing 10% foetal bovine serum the activity of the enzyme decreases as the culture density increases and the cells attain final densities of about 5 X 10(4) cells/cm2.