title: Effects of depletion of K+, Na+, or Ca2+ on DNA synthesis and cell cation content in chick embryo fibroblasts.
abstract: Decreasing the K+ concentration of the medium from 5 mM to 0.59 mM decreased the K+ content of chick embryo fibroblasts to 22% of control values and increased the Na+ content to 820% of control values. The alteration of monovalent cation content occurred within two hours but had no effect on the rate of DNA synthesis, as measured by 3H-thymidine incorporation, for at least 16 hours. By decreasing the Na+ concentration in the medium, a 50% reduction in cellular Na+ could be obtained with no effect on thymidine incorporation. Since these changes in cellular Na+ or K+ are much larger than any known to occur under physiological conditions but have no effect on thymidine incorporation, we conclude that Na+ and K+ do not play a critical role in determining multiplication rate. Addition of 1.8 mEGTA to cells in media containing 1.7 mM Ca2+ and 0.8 mM Mg2+ inhibited thymidine incorporation and sharply decreased cellular K+ and increased cellular Na+ content. However, there was no reduction in total cellular Ca2+ levels. Likewise, decreasing the Ca2+ concentration of the medium below 0.01 mM inhibited thymidine incorporation, decreased cellular K+ and Mg2+, and increased cellular Na+ but did not affect total cellular Ca2+ levels. Inhibition of DNA synthesis, therefore, could not be correlated with changes in cellular Ca2+ levels.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D003470:Culture Media; D046508:Culture Techniques; D004247:DNA / Q000096:biosynthesis*; D004533:Egtazic Acid / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D003470:Culture Media; D004533:Egtazic Acid; D004247:DNA; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium