TRPV6 and Ca1.3 Mediate Distal Small Intestine Calcium Absorption Before Weaning.

BACKGROUND & AIMS: Intestinal Ca absorption early in life is vital to achieving optimal bone mineralization. The molecular details of intestinal Ca absorption have been defined in adults after peak bone mass is obtained, but they are largely unexplored during development. We sought to delineate the molecular details of transcellular Ca absorption during this critical period.

METHODS

Expression of small intestinal and renal calcium transport genes was assessed by using quantitative polymerase chain reaction. Net calcium flux across small intestinal segments was measured in Ussing chambers, including after pharmacologic inhibition or genetic manipulation of TRPV6 or Ca1.3 calcium channels. Femurs were analyzed by using micro-computed tomography and histology.

RESULTS

Net TRPV6-mediated Ca flux across the duodenum was absent in pre-weaned (P14) mice but present after weaning. In contrast, we found significant transcellular Ca absorption in the jejunum at 2 weeks but not 2 months of age. Net jejunal Ca absorption observed at P14 was not present in either Trpv6 mutant (D541A) mice or Ca1.3 knockout mice. We observed significant nifedipine-sensitive transcellular absorption across the ileum at P14 but not 2 months. Ca1.3 knockout pups exhibited delayed bone mineral accrual, compensatory nifedipine-insensitive Ca absorption in the ileum, and increased expression of renal Ca reabsorption mediators at P14. Moreover, weaning pups at 2 weeks reduced jejunal and ileal Ca1.3 expression.

CONCLUSIONS

We have detailed novel pathways contributing to transcellular Ca transport across the distal small intestine of mice during development, highlighting the complexity of the multiple mechanisms involved in achieving a positive Ca balance early in life.