title: Magnesium reverses inhibitory effects of calcium deprivation on coordinate response of 3T3 cells to serum.
abstract: Deprivation of Ca(2+) in crowded cultures of 3T3 cells inhibits the onset of DNA synthesis. By raising [Mg(2+)] to 15 mM the inhibition produced by Ca(2+) deprivation can be fully overcome. Sparse cultures are not inhibited by a similar deprivation of Ca(2+), and therefore are not stimulated by supranormal [Mg(2+)]. The time course of stimulation of the onset of DNA synthesis by supranormal [Mg(2+)] in low [Ca(2+)] is the same as that produced by serum in physiological concentrations of Ca(2+) and Mg(2+). Concentrations of Mg(2+) > 20 mM in low [Ca(2+)] reverse the stimulation, and [Mg(2+)] >/= 30 mM kills many cells. In contrast to the stimulation by 15 mM Mg(2+), supranormal [Ca(2+)] has no effect on the onset of DNA synthesis in cultures inhibited by Mg(2+) deprivation, if the formation of insoluble Ca-P(i) complexes is prevented. Neither Na(+) nor K(+) reproduces the effects of Mg(2+). The uptake of uridine is another parameter of the coordinate response of 3T3 cells to serum stimulation that is inhibited by Ca(2+) deprivation, and supranormal [Mg(2+)] also reverses this inhibition. The results support the thesis that the coordinate response of growth and metabolism to external effectors is regulated by the availability of Mg(2+) within the cell and that the inhibitory effects of Ca(2+) deprivation are indirect and caused by a reduction in the availability of Mg(2+).
mesh_terms: D001769:Blood; D002118:Calcium / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D003260:Contact Inhibition / Q000187:drug effects; D003470:Culture Media; D004247:DNA / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008722:Methods; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
chemical_list: D003470:Culture Media; D004247:DNA; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium