Possible Involvement of Amiloride-Sensitive Na⁺/H⁺ Exchanger and/or Na⁺ Transport Systems in Hatching and the Trophoblast Spreading in Mouse Blastocysts Cultured in vitro

抄録

In mouse blastocysts cultured in vitro, trophoblast cells undergo extensive spreading which represents the invasion stage of implantation in vivo. The trophoblast spreading is accompanied by striking increase of cellular volume and transformation of the cells into the giant trophoblast cells. Since, Na⁺/H⁺ exchanger system (or Na⁺/H⁺ antiporter) on the plasma membrane of vertebrate cells plays a crucial role in regulating cellular volume in mammalian cells, the carrier mediated Na⁺/H⁺ exchanger system might be involved in the process of trophoblast spreading. To obtain clues to approach the problem, we examined effects of amiloride which is a potent inhibitor of Na⁺/H⁺ exchanger and other amiloride sensitive Na⁺ channels, upon mouse blastocysts cultured in vitro. Amiloride inhibited, in dose-dependent manner, hatching as well as the trophoblast spreading in mouse blastocysts cultured in vitro. Our findings strongly indicated that the amiloride sensitive Na⁺/H⁺ exchanger system might be operating, in particular, during the initial phase of trophoblast spreading: the system appeared less active in the fully spread cells. To corroborate the view, experiments with more specific inhibitors of Na⁺/H⁺ exchanger are currently in progress in our laboratory. In addition, while amiloride and its derivatives have been used as diuretic drugs, little has been known concerning their effects upon the peri-implantation embryos. Our data clearly indicates their potentially adverse effects upon the conceptuses during early phase of gestation.