Evidence for the presence of sodium- and potassium-dependent adenosine triphosphatase alpha1 and beta1 subunit isoforms and their probable role in blastocyst expansion in the preattachment horse conceptus.

The research investigates the role of sodium- and potassium-dependent adenosine triphosphatase (Na+,K+-ATPase) in the fluid accumulation in horse embryos. It concludes that, despite the unusually low salt concentration in the fluid, this enzyme is a key player in the process, much as it is in other species.

Research Objective and Methods

• The research was started in response to the unique hypotonicity, or low salt concentration, in the fluid of horse blastocysts – a stage of early embryonic development. Specifically, the scientists sought to study the function of an enzyme known as Na+,K+-ATPase in this process, as it helps in maintaining balance of sodium and potassium ions inside and outside the cells.
• To do this, the researchers conducted a variety of experiments on conceptuses (early embryos) from nine mares, which were recovered between 12 and 28 days after ovulation.
• In one test, they performed a reverse transcriptase polymerase chain reaction (RT-PCR), which is a technique often used to detect genetic material in an organism.
• They also conducted Western blot analysis, a method used to detect specific proteins in a tissue sample. Here it was used to confirm the presence of alpha1 and beta1 subunits of the Na+,K+-ATPase enzyme in the Day 15 conceptuses.
• In another experiment, they applied immunohistochemical staining to trophoblast tissues from the conceptuses. This is a process that uses antibodies to detect the presence of specific proteins in tissues.
• Finally, they prepared trophoblastic vesicles from the conceptuses and used cytochalasin D and ouabain – substances that can inhibit cell expansion and the activity of the Na+,K+-ATPase enzyme respectively – to investigate how altering the enzyme’s activity would affect blastocyst expansion.

Findings and Conclusion

• The researchers found mRNA encoding the alpha1 and beta1 subunit isoforms of Na+,K+-ATPase in all embryonic tissues examined. This indicated the presence of this enzyme in the tissue.
• The Western blot and immunohistochemical tests confirmed the results of the RT-PCR technique, with both alpha1 and beta1 subunits present.
• In their experiments on trophoblastic vesicles, they observed that when the enzyme was inhibited with ouabain, expansion of these structures decreased. On the other hand, in a normal medium (where the enzyme was functioning), there was a 3-fold increase in expansion, despite a partial collapse induced by cytochalasin D.
• This led the scientists to conclude that Na+,K+-ATPase plays a significant role in the accumulation of fluid in horse conceptuses, in line with other species, despite the fluid’s low salt concentration.