REDISTRIBUTION OF K+ IN CLEAVING EGGS OF A FISH MISGURNUS FOSSILIS

In leaving eggs of loach, a redistribution of K+ occurs which leads to K+ ion accumulation in the embryo (blastoderm) at the expense of yolk. Na+ content of embryos does not increase. As a result, a significant rise in K+ Na+ ratio occurs in embryos, which reaches a constant value by the mid-blastula stage. This occurs also during the cleavage of X-ray irradiated eggs suggesting that K+ redistribution is independent of nuclear genetic function. Ionic composition of embryos is maintained by an active, energy-linked mechanism which apparently involves a (Na+-K+) ATPase since ouabain (a specific inhibitor of (Na+-K+)ATPase of membranes) causes a loss of K+ from the cells. K+ ion accumulation and the attainment of a constant K+ Na+ ratio are correlated with a drop in mitotic index and with the onset of RNA synthesis in the cell nuclei. The results are consistent with the proposal that the increase in K+ Na+ ratio may play a part in switching over the nucleic acid synthesis from replication to transcription path. © 1969.