Functional TRPV6 channels are crucial for transepithelial Ca 2+ absorption

• Published in: American journal of physiology: Gastrointestinal and liver physiology 2012-10, Vol.303 (7), p.G879-G885
• Main Authors: Woudenberg-Vrenken, Titia E., Lameris, Anke L., Weißgerber, Petra, Olausson, Jenny, Flockerzi, Veit, Bindels, René J. M., Freichel, Marc, Hoenderop, Joost G. J.
• Format: Article
• Language: English
• ISSN: 0193-1857; 1522-1547
• DOI: 10.1152/ajpgi.00089.2012

TRPV6 is considered the primary protein responsible for transcellular Ca 2+ absorption. In vitro studies demonstrate that a negatively charged amino acid (D) within the putative pore region of mouse TRPV6 (position 541) is critical for Ca 2+ permeation of the channel. To elucidate the role of TRPV6 in transepithelial Ca 2+ transport in vivo, we functionally analyzed a TRPV6 D541A/D541A knockin mouse model. After weaning, mice were fed a regular (1% wt/wt) or Ca 2+ -deficient (0.02% wt/wt) diet and housed in metabolic cages. Blood was sampled for Ca 2+ measurements, and the expression of Ca 2+ transport proteins was analyzed in kidney and duodenum. Intestinal 45 Ca 2+ uptake was measured in vivo by an absorption assay. Challenging the mice with the Ca 2+ -deficient diet resulted in hypocalcemia in wild-type and TRPV6 D541A/D541A mice. On a low-Ca 2+ diet both mouse strains displayed increased expression of intestinal TRPV6, calbindin-D 9K , and renal TRPV5. TRPV6 D541A/D541A mice showed significantly impaired intestinal Ca 2+ uptake compared with wild-type mice, and duodenal TRPV5 expression was increased in TRPV6 D541A/D541A mice. On a normal diet, serum Ca 2+ concentrations normalized in both mouse strains. Under these conditions, intestinal Ca 2+ uptake was similar, and the expression levels of renal and intestinal Ca 2+ transport proteins were not affected. We demonstrate that TRPV6 D541A/D541A mice exhibit impaired transcellular Ca 2+ absorption. Duodenal TRPV5 expression was increased in TRPV6 D541A/D541A mice, albeit insufficient to correct for the diminished Ca 2+ absorption. Under normal conditions, when passive Ca 2+ transport is predominant, no differences between wild-type and TRPV6 D541A/D541A mice were observed. Our results demonstrate a specific role for TRPV6 in transepithelial Ca 2+ absorption.