Na+, K+, ATPase activity in the human and bovine preimplantation embryo

Blastocyst formation is associated with a marked increase in ATP production, much of which is thought to be associated with the active transport of ions across the trophectoderm mediated by the sodium pump (Na+, K+, ATPase) resulting in the vectorial transport of water into the blastocoel. In this study, the biochemical activity of the sodium pump was measured directly in single human and bovine embryo extracts by monitoring the conversion of ATP to ADP in the presence and absence of ouabain. ATP and ADP were assayed by HPLC. In both species, there was a transient, significant increase in sodium pump activity while the blastocyst was actively expanding. The oxygen consumption of single human blastocysts was measured in order to estimate the proportion of total ATP used by the Na+, K+, ATPase. The results suggest that approximately 60 and 36% of the ATP produced is used by the sodium pump during blastocoel expansion in the human and bovine blastocyst, respectively.