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Functional TRPV6 channels are crucial for transepithelial Ca2+ absorption Woudenberg-Vrenken TE; Lameris AL; Weissgerber P; Olausson J; Flockerzi V; Bindels RJ; Freichel M; Hoenderop JGAm J Physiol Gastrointest Liver Physiol 2012[Oct]; 303 (7): G879-85TRPV6 is considered the primary protein responsible for transcellular Ca2+ 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 Ca2+ permeation of the channel. To elucidate the role of TRPV6 in transepithelial Ca2+ transport in vivo, we functionally analyzed a TRPV6D541A/D541A knockin mouse model. After weaning, mice were fed a regular (1% wt/wt) or Ca2+-deficient (0.02% wt/wt) diet and housed in metabolic cages. Blood was sampled for Ca2+ measurements, and the expression of Ca2+ transport proteins was analyzed in kidney and duodenum. Intestinal 45Ca2+ uptake was measured in vivo by an absorption assay. Challenging the mice with the Ca2+-deficient diet resulted in hypocalcemia in wild-type and TRPV6D541A/D541A mice. On a low-Ca2+ diet both mouse strains displayed increased expression of intestinal TRPV6, calbindin-D(9K), and renal TRPV5. TRPV6D541A/D541A mice showed significantly impaired intestinal Ca2+ uptake compared with wild-type mice, and duodenal TRPV5 expression was increased in TRPV6D541A/D541A mice. On a normal diet, serum Ca2+ concentrations normalized in both mouse strains. Under these conditions, intestinal Ca2+ uptake was similar, and the expression levels of renal and intestinal Ca2+ transport proteins were not affected. We demonstrate that TRPV6D541A/D541A mice exhibit impaired transcellular Ca2+ absorption. Duodenal TRPV5 expression was increased in TRPV6D541A/D541A mice, albeit insufficient to correct for the diminished Ca2+ absorption. Under normal conditions, when passive Ca2+ transport is predominant, no differences between wild-type and TRPV6D541A/D541A mice were observed. Our results demonstrate a specific role for TRPV6 in transepithelial Ca2+ absorption.|*Calcium/blood/pharmacokinetics[MESH]|Animals[MESH]|Calbindins[MESH]|Calcium Channels/*metabolism[MESH]|Calcium-Binding Proteins/metabolism[MESH]|Diet/adverse effects/methods[MESH]|Hypocalcemia/metabolism[MESH]|Intestinal Absorption/*physiology[MESH]|Intestinal Mucosa/physiology[MESH]|Kidney/metabolism[MESH]|Mice[MESH]|Mice, Knockout[MESH]|S100 Calcium Binding Protein G/*metabolism[MESH]|TRPV Cation Channels/genetics/*metabolism[MESH]|Transcytosis[MESH] |
