Expression of TRPV6 and CaBP-D28k in the egg shell gland (uterus) during the oviposition cycle of the laying hen

1. The aim of this study was to investigate the localisation of the transient receptor potential vanilloid channel type 6 (TRPV6) in egg shell gland (ESG) and examine the dynamic expression of TRPV6 and Calbindin-d28k (CaBP-D28k), as well as the changes in concentration of total calcium (Ca), total inorganic phosphorus (P), alkaline phosphatase (ALP), parathyroid hormone (PTH) and calcitonin (CT) in plasma during the oviposition cycle. 2. The plasma ALP activity was notably increased at 8h. In addition, plasma CT was highest at 0h and significantly lower at 8h. The change of plasma PTH concentration increased slightly post-oviposition and reached a maximum at 16h. 3. Immunohistochemical analysis indicated that TRPV6 was strongly localised to the apical luminal epithelium of the mucosa. The mRNA levels of TRPV6 and CaBP-D28k in the ESG remained very low from 0 to 4.5h, but were significantly increased at 16h. Furthermore, Western blotting analysis showed that the expression of TRPV6 and CaBP-D28k also reached a maximum at 16h and was different from the concentration of CaBP-D28k. 4. In conclusion, the epithelial Ca2+ channel TRPV6 is strongly expressed in the epithelial cells of the eggshell gland, and the increase of TRPV6 and CaBP-D28k mRNA and protein expression during eggshell formation suggests that active Ca2+ transcellular transport exerts significant effects in delivering active calcium in the ESG.