Abstract
The platelet-derived growth factor (PDGF), a potent mitogen for normal human fibroblasts, shows reduced activity in medium containing regular levels of Ca++. A double reciprocal plot of the growth rate of IMR-90 cells versus the Ca++ concentration in the presence or absence of PDGF showed a common intercept on the ordinate, which gives a minimum doubling time of 20 h for middle aged cells. This is evidence of a competitive growth stimulation by PDGF and Ca++ that differs from the non-competitive mode of action of EGF by which is also reduced the requirement of extracellular Ca++ for normal human cell growth.
