The activity of Na+/K(+)-ATPase and abundance of its mRNA are regulated in rat myometrium during pregnancy.

The Na+/K(+)-ATPase activity and expression of mRNAs encoding alpha and beta subunits of the enzyme were examined in rat myometrium at different stages of pregnancy. The enzyme activity appeared to increase during the pregnancy and reached the highest value at the 17th day. Northern blot analysis of total RNA isolated from the same myometrial samples shows the expressions of alpha 1, alpha 3 and beta mRNAs. A2 mRNA was not detectable. By the progression of pregnancy until the 17th day the expression of all the three kinds of mRNA increased. The change in the abundance of mRNA-beta was much more higher (12-fold) than that of mRNA-alpha 1 and -alpha 3 (4 and 2.5-fold, respectively). Furthermore, the expression of mRNA-beta sharply decreased after the 17th day, while the level of alpha subunits mRNAs barely changed. We conclude that transcriptional regulation of the Na+/K(+)-ATPase subunits could be different during this physiological process.