Induction of growth in resting fibroblastic cell cultures by Ca++.

Of all the components of the culture medium, only CaCl2 induces DNA replication when added to resting cultures of Balb/c 3T3 cells. The effect is present even in a serum-free medium. Increasing the Ca++ concentration above the standard 1.8 mM in the medium of a new culture increases the total number of cells ultimately produced, without affecting the initial cell growth rate. This effect is synergistic with that of serum. The elevated Ca++ concentration also induces striking morphological changes. The Ca++ effect could not be reproduced by a Ca++ ionophore. These observations afford a new tool for studying how the various intracellular events following the addition of growth factors to resting cultures are involved in the control of cellular growth.