Calcium, magnesium, and serum factors in multiplication of normal and transformed human lung fibroblasts.

Serum factors determine the extracellular requirement for both Ca2+ and Mg2+ for multiplication of normal human lung fibroblasts in vitro. Serum factors also affect the extracellular Ca2+ requirement for transformed fibroblasts but to a different extent than for normal cells. Transformed cells exhibit a reduced requirement for both Ca2+ and Mg2+ for multiplication. The apparent reduction in Ca2+ requirement of transformed cells is dependent on the level of serum factors in the medium. The reduced Mg2+ requirement for transformed cells is more striking than the loss of Ca2+ and independent of the level of serum factors in the medium. A sequential effector relationship among serum factors, Ca2+ and Mg2+, in a proliferative control system for normal cells is proposed. Alteration or bypass of an intracellular Mg2+-requiring process is proposed as a major lesion in the transformed cells. This alteration causes an observed loss of requirements for both Ca2+ and serum factors for the multiplication of transformed cells.