Analysis of Na+ concentration patterns in trophectoderm cells of mouse blastocysts using a dual-wavelength...

The developmental process of the mammalian blastocyst involves the intricate interplay of cellular and molecular mechanisms, including electrolyte dynamics within the trophectoderm (TE). We hypothesized that sodium (Na+) is actively transported from the TE into the blastocyst cavity, driving water influx and promoting blastocyst expansion. In this study, we investigated the dynamics of Na+ concentration in the TE of mouse embryos using sodium-binding benzofuran isophthalate (SBFI), a dual-wavelength Na+-sensitive fluorescent indicator. Observations revealed three distinct patterns of Na+ dynamics, each correlating with variations in blastocyst cross-sectional area and developmental outcomes. Embryos exhibiting an initial decrease followed by stabilization of Na+ concentration (Group A) demonstrated the highest rates of hatching, suggesting a relationship between Na+ flux and successful embryonic development. In contrast, embryos with transient increases (Group B) displayed reduced hatching rates and developmental progression. Further, the inhibition of Na+/K+-ATPase activity disrupted Na+ flux and blastocyst cavity expansion, emphasizing its critical role in blastocyst formation. This study highlights the potential of dual-wavelength imaging for elucidating electrolyte dynamics in preimplantation embryos and its implications for optimizing embryo culture systems in reproductive medicine.