title: Regulation of the epithelial Ca2+ channels in small intestine as studied by quantitative mRNA detection.
abstract: The epithelial Ca2+ channels TRPV5 and TRPV6 are localized to the brush border membrane of intestinal cells and constitute the postulated rate-limiting entry step of active Ca2+ absorption. The aim of the present study was to investigate the hormonal regulation of these channels. To this end, the effect of 17beta-estradiol (17beta-E2), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and dietary Ca2+ on the expression of the duodenal Ca2+ transport proteins was investigated in vivo and analyzed using realtime quantitative PCR. Supplementation with 17beta-E2 increased duodenal gene expression of TRPV5 and TRPV6 but also calbindin-D9K and plasma membrane Ca2+-ATPase (PMCA1b) in ovariectomized rats. 25-Hydroxyvitamin D3-1alpha-hydroxylase (1alpha-OHase) knockout mice are characterized by hyperparathyroidism, rickets, hypocalcemia, and undetectable levels of 1,25(OH)2D3 and were used to study the 1,25(OH)2D3-dependency of the stimulatory effects of 17beta-E2. Treatment with 17beta-E2 upregulated mRNA levels of duodenal TRPV6 in these 1alpha-OHase knockout mice, which was accompanied by increased serum Ca2+ concentrations from 1.69 +/- 0.10 to 2.03 +/- 0.12 mM (P < 0.05). In addition, high dietary Ca2+ intake normalized serum Ca2+ in these mice and upregulated expression of genes encoding the duodenal Ca2+ transport proteins except for PMCA1b. Supplementation with 1,25(OH)2D3 resulted in increased expression of TRPV6, calbindin-D9K, and PMCA1b and normalization of serum Ca2+. Expression levels of duodenal TRPV5 mRNA are below detection limits in these 1alpha-OHase knockout mice, but supplementation with 1,25(OH)2D3 upregulated the expression to significant levels. In conclusion, TRPV5 and TRPV6 are regulated by 17beta-E2 and 1,25(OH)2D3, whereas dietary Ca2+ is positively involved in the regulation of TRPV6 only.
authors.affiliation: Department of Cell Physiology, Niujmegen Center for Molecular Life Sciences, University Medical Center Nijmegen, P. O. Box 9101, NL-6500 HB Nijmegen, The Netherlands.
authors.forename: Monique
authors.initials: M
authors.lastname: van Abel
authors.forename: Joost G J
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: Annemiete W C M
authors.initials: AW
authors.lastname: van der Kemp
authors.forename: Johannes P T M
authors.initials: JP
authors.lastname: van Leeuwen
authors.forename: Rene J M
authors.initials: RJ
authors.lastname: Bindels
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000235:genetics* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics* / Q000378:metabolism*; D002136:Calcium, Dietary / Q000494:pharmacology; D004386:Duodenum / Q000166:cytology / Q000378:metabolism; D004958:Estradiol / Q000097:blood / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000502:physiology; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010052:Ovariectomy; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D050916:TRPV Cation Channels
chemical_list: D015220:Calcium Channels; D002136:Calcium, Dietary; D012333:RNA, Messenger; D050916:TRPV Cation Channels; C492241:TRPV5 protein, rat; C120776:TRPV6 channel; C492240:Trpv5 protein, mouse; D004958:Estradiol; D002117:Calcitriol; D002118:Calcium