Differential expression of uterine calcium transporter 1 and plasma membrane Ca2+ ATPase 1b during rat estrous cycle.

Calcium-related proteins include the calcium transporters 1 and 2 (CaT1 and CaT2), plasma membrane Ca2+-ATPase 1b (PMCA1b), and calbindin-D9k and -D28k. The expression of CaT1 and PMCA1b and their potential roles in the uterine tissue remain to be clarified. Thus, in the present study, the expression patterns of CaT1 and PMCA1b were examined to predict their roles in rat uterus during the estrous cycle. Both CaT1 and PMCA1b mRNAs were detected in rat uterus. Uterine CaT1 mRNA was highly expressed at diestrus compared with proestrus, whereas PMCA1b expression was not altered during the estrus cycle. To evaluate the sex steroids involved in uterine CaT1 mRNA regulation, 17beta-estradiol (E2) and/or progesterone (P4) were injected into immature rats. Treatment with P4 or E2 plus P4 resulted in an increase in CaT1 mRNA, but a synergetic effect of E2 plus P4 was not detected. Uterine CaT1 mRNA was induced by P4 in a time- and dose-dependent manner, with maximal transcript detected 12 h after the final P4 injection. Treatment with RU486, a progesterone receptor (PR) antagonist, completely blocked P4-induced CaT1 mRNA, indicating that P4 regulates CaT1 mRNA expression via a PR-mediated pathway. In addition, CaT1 mRNA was expressed in uterine endometrium and glandular endometrium at diestrus in P4-treated rats. Together, these results suggest that CaT1 is regulated by P4 at diestrus via a PR-dependent pathway.