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Magnesium Reverses Inhibitory Effects of Calcium Deprivation on Coordinate Response of 3T3 Cells to Serum

A. H. Rubin, M. Terasaki and H. Sanui
Proceedings of the National Academy of Sciences of the United States of America
Vol. 75, No. 9 (Sep., 1978), pp. 4379-4383
Stable URL: http://www.jstor.org/stable/68554
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Magnesium Reverses Inhibitory Effects of Calcium Deprivation on Coordinate Response of 3T3 Cells to Serum
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Abstract

Deprivation of Ca2+ in crowded cultures of 3T3 cells inhibits the onset of DNA synthesis. By raising [Mg2+] to 15 mM the inhibition produced by Ca2+ deprivation can be fully overcome. Sparse cultures are not inhibited by a similar deprivation of Ca2+, and therefore are not stimulated by supranormal [Mg2+]. The time course of stimulation of the onset of DNA synthesis by supranormal [Mg2+] in low [Ca2+] is the same as that produced by serum in physiological concentrations of Ca2+ and Mg2+. Concentrations of Mg2+ > 20 mM in low [Ca2+] reverse the stimulation, and [Mg2+] ≥ 30 mM kills many cells. In contrast to the stimulation by 15 mM Mg2+, supranormal [Ca2+] has no effect on the onset of DNA synthesis in cultures inhibited by Mg2+ deprivation, if the formation of insoluble Ca-Pi complexes is prevented. Neither Na+ nor K+ reproduces the effects of Mg2+. The uptake of uridine is another parameter of the coordinate response of 3T3 cells to serum stimulation that is inhibited by Ca2+ deprivation, and supranormal [Mg2+] 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 Mg2+ within the cell and that the inhibitory effects of Ca2+ deprivation are indirect and caused by a reduction in the availability of Mg2+.

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