Localization and regulation of the epithelial Ca2+ channel TRPV6 in the kidney

The family of epithelial Ca2+ channels consists of two highly homologues members, TRPV5 and TRPV6, which constitute the apical Ca2+ entry mechanism in active Ca2+ (re)absorption in kidney and small intestine. In kidney, TRPV5 expression has been extensively studied, whereas TRPV6 localization and regulation has been largely confined to the small intestine. The present study investigated the renal distribution of TRPV6 and regulation by 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3). In mouse kidney, TRPV6 was detected by immunohistochemistry at the apical domain of the distal convoluted tubules (DCT2), connecting tubules (CNT), and cortical and medullary collecting ducts (CD). Furthermore, several putative vitamin D-responsive elements were detected upstream of the mouse TRPV6 start codon, and 1,25(OH)2D3 treatment significantly increased renal TRPV6 mRNA and protein expression. In DCT2 and CNT, TRPV6 co-localizes with the other known Ca2+ transport proteins, including TRPV5 and calbindin-D-28K. Together, these data suggest a role for TRPV6 in 1,25(OH)(2)D-3-stimulated Ca2+ reabsorption in these segments. Interestingly, distribution of TRPV6 extended to the CD, where it localized to the apical domain of principal and intercalated cells, which are not generally implicated in active Ca2+ reabsorption. In addition, TRPV6 mRNA levels were quantified in a large set of tissues, and in the order of decreasing expression level were detected: prostate > stomach, brain > lung > duodenum, kidney, bone, cecum, heart > colon > skeletal muscle > pancreas. Therefore, additional physiologic functions for TRPV6 are feasible. In conclusion, TRPV6 is expressed along the apical domain of DCT2, CNT, and CD, where TRPV6 expression is positively regulated by 1,25(OH)(2)D-3.