High potassium concentration improves preimplantation development of mouse embryos in vitro.

Embryo growth in vitro in culture media containing potassium (K) ions at the concentration found in common extracellular fluids proceeds at a slower pace than in vivo. Considering that oviductal fluid has an unusually high concentration of K, the effect of various concentrations of this ion on development of mouse embryos in vitro was investigated. Two-cell to 4-cell preimplantation mouse embryos were cultured in vitro for 47 hours in a medium in which NaCl was partially replaced by KCl at concentrations ranging from 4.7 to 60 mM. The number of cells per embryo increased in a dose-related fashion when the embryos were cultured in the presence of 4.7, 10, and 25 mM of K. Higher K concentrations were detrimental for development. Embryos developed in vitro under different concentrations of K were transferred to pseudopregnant recipient foster mothers as a test of viability. The highest rate of implantation was observed with embryos cultured in medium containing 25 mM K. The results indicate that a high concentration of K in the culture medium (25 mM), comparable to that found in the genital tract of the female mouse, is required for a rate of development in vitro similar to the one observed in vivo.