Roles of Na+/K+-ATPase, Na+ channel and Na+/H+ exchanger in the re-expansion of contracted mouse blastocysts
1998
Takeuchi, T. (Niigata Univ. (Japan)) | Niimura, S.
The influence of inhibitors to Na+ transporters on the contraction of culturedmouse blastocysts was observed by time-lapse videomicrography, and the mechanism of re-expansion of contracted blastocysts was examined. The activity of Na+/K+-ATPase in contracted blastocysts was also demonstrated histochemically. The activity of Na+/K+-ATPase was significantly more often detected in contracted blastocysts (83.3%), compared with control expanded blastocysts (30.0%). A strong Na+/K+-ATPase activity was observed in most of those contracted blastocysts. The number of contractions until 32 hours after blastocyst formation was 5.68 times in blastocysts cultured with ouabain, an inhibitor of Na+/K+-ATPase, 5.53 times in those cultured with benzamil, an inhibitor of Na+ channel, and 5.43 times in those cultured with EIPA, an inhibitor of Na+/H+ exchanger, consistently showing a significantly fewer number, compared with that observed in control blastocysts cultured in a medium containing none of these inhibitors. Blastocysts treated with ouabain, benzamil and EIPA required 6.15, 5.65 and 5.77 hours, respectively, to re-expand to the size before contraction, all showing a significantly prolonged time, compared with the length of time taken to re-expand by the control blastocysts cultured without any of these inhibitors. From these results, it was suggested that contracted blastocysts re-expand as Na+ contained in trophoblast cells is actively transported into and accumulated in the blastocoel fluid by the action of Na+/K+ATPase activated in the trophoblast cell membrane. In addition, Na+ necessary for blastocyst re-expansion was thought to be transported into trophoblast cells through Na+ channel and Na+/H+ exchanger from the outside of blastocysts
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