186 DUODENAL AND RENAL TRANSIENT RECEPTOR POTENTIAL VANILLOID 6 APPEAR TO BE DISTINCTLY REGULATED BY SEX STEROID HORMONES, ESTROGEN AND PROGESTERONE, IN IMMATURE FEMALE RATS

Abstract

Calcium-related proteins include transient receptor potential vanilloid (TRPV) 5 and 6, plasma membrane calcium-ATPase 1b (PMCA1b), and calbindin-D9k and -D28k. The TRPV6 is a major calcium channel located in the apical and basolateral membranes of cell and distributed widely in many other organs, especially in the exocrine tissues such as intestine and uterus. TRPV6s are generally regulated by vitamin D, a dietary calcium ion and hormone. In particular, uterine TRPV6 appears to be affected by sex steroid hormones, which are altered according to estrous cycle and pregnancy. In order to discover the effect of sex steroid hormones on the regulation of TRPV6, we examined the expression of TRPV6 mRNA by using RT-PCR and real-time PCR, and protein expression of TRPV6 by immunohistochemistry (IHC) in the uterus, duodenum, and kidney. To evaluate the effect(s) of sex steroid hormones on its uterine, duodenal, and renal regulation, 17β-estradiol [E2; 40 μg kg^–1 of body weight (bw)] and/or progesterone (P4; 4 mg kg^–1 of bw) or vehicle (n = 6/each group) were subcutaneously injected into Sprague-Dawley immature female rats (14 days old, n = 24 in total) for 3 days. As a result, the treatments of immature rats with E2 or P4 increased TRPV6 mRNA for calcium function or regulation in the uterus of immature rats. To confirm the specificity of E2 or P4 through their receptors, we treated the immature rats (extra n = 24 in total) with an estrogen receptor-antagonist, ICI 182,780 (ICI; 30 μg kg^–1 of bw), and/or progesterone receptor antagonist, RU 486 (10 mg kg^–1 of bw), at 3 days prior to E2 or P4 injection. Consequently, an increase in TRPV6 mRNA was observed in the following 2 treatments; ICI plus E2/P4 and E2/P4 alone. In IHC, we further observed that the expression of duodenal TRPV6 was increased by E2 or P4 and E2 or P4 plus ICI, while no difference was observed in renal TRPV6 by the treatments of sex steroid hormones. In conclusion, these results indicate that the expressions of uterine and duodenal TRPV6 may be induced by E2 and P4, but its renal expression may not be controlled by these steroids.