Fluctuation in the intracellular concentration of Na+ and Cl− but not of K+ or Mg2+ at mitosis of the first cell cycle in fertilized sea urchin eggs

Abstract This report concerns changes in the cytoplasmic concentration of Na + , Cl − , K + and Mg 2+ during the first cell cycle and into the second cell cycle of fertilized sea urchin eggs of Lytechinus variegatus . The results of electron probe x-ray microanalysis showed a significant equimolar decrease in Na + and Cl − at the first cell division which was followed by a significant increase early in the second cell cycle. Neither K + nor Mg 2+ showed such significant changes. The loss of a large fraction of the Na + ions from the egg at metaphase was not accompanied by a significant egg volume change. The observed pattern of ionic change was related to several previously reported chemical and metabolic changes at cell division in sea urchin eggs.