Aging of human epidermal keratinocytes was studied by serial passaging them as a
monolayer culture in a serum-free medium containing 0.09 M calcium. Under these
conditions the cells were constantly kept in a proliferative mode and in an undifferentiated
state. Aging characteristics in terms of growth and longevity, cumulative population doubling
level, cell yield, protein content, and alterations in morphology and in macromolecular
synthesis were studied. Furthermore, the induction of differentiation by raising the calcium …