INTRACELLULAR ION CONCENTRATIONS AND THEIR MAINTENANCE BY NA+ K+-ATPASE IN PREIMPLANTATION MOUSE EMBRYOS/

We have measured the amounts of Na+, K+ and C- in preimplantation mous e embryos (1-cell, 2-cell and morula) using electron probe X-ray micro analysis. The levels of these ions do not vary much over this period, and are approximately the same as those found in other mammalian cells , contrary to previous reports. We have confirmed that preimplantation embryos exhibit Na+/K+-ATPase activity at all stages examined, and ha ve shown that the ATPase maintains high K+/Na+ ratios (12-16) in all t hese embryonic stages, comparable to those seen in other healthy cells ; this is in contrast to the low ratios reported in earlier work. Inhi bition of the Na+/K+-ATPase results in the slow exchange of intracellu lar K+ for extracellular Naf (half-time approximately 5h), indicating that Na+/K+-ATPase activity maintains steep Na+ and K+ gradients in pr eimplantation mouse embryos as it does in most other cells.