title: Segmental transport of Ca²⁺ and Mg²⁺ along the gastrointestinal tract.
abstract: Calcium (Ca(2+)) and magnesium (Mg(2+)) ions are involved in many vital physiological functions. Since dietary intake is the only source of minerals for the body, intestinal absorption is essential for normal homeostatic levels. The aim of this study was to characterize the absorption of Ca(2+) as well as Mg(2+) along the gastrointestinal tract at a molecular and functional level. In both humans and mice the Ca(2+) channel transient receptor potential vanilloid subtype 6 (TRPV6) is expressed in the proximal intestinal segments, whereas Mg(2+) channel transient receptor potential melastatin subtype 6 (TRPM6) is expressed in the distal parts of the intestine. A method was established to measure the rate of Mg(2+) absorption from the intestine in a time-dependent manner by use of (25)Mg(2+). In addition, local absorption of Ca(2+) and Mg(2+) in different segments of the intestine of mice was determined by using surgically implanted intestinal cannulas. By these methods, it was demonstrated that intestinal absorption of Mg(2+) is regulated by dietary needs in a vitamin D-independent manner. Also, it was shown that at low luminal concentrations, favoring transcellular absorption, Ca(2+) transport mainly takes place in the proximal segments of the intestine, whereas Mg(2+) absorption predominantly occurs in the distal part of the gastrointestinal tract. Vitamin D treatment of mice increased serum Mg(2+) levels and 24-h urinary Mg(2+) excretion, but not intestinal absorption of (25)Mg(2+). Segmental cannulation of the intestine and time-dependent absorption studies using (25)Mg(2+) provide new ways to study intestinal Mg(2+) absorption.
authors.affiliation: Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands;
authors.forename: Anke L
authors.initials: AL
authors.lastname: Lameris
authors.affiliation: School of Medicine, University of Tampere, Tampere, Finland; Department of Internal Medicine, Tampere University Hospital, Tampere, Finland;
authors.forename: Pasi I
authors.initials: PI
authors.lastname: Nevalainen
authors.affiliation: Central Animal Facility, Radboud University, Nijmegen, The Netherlands; and.
authors.forename: Daphne
authors.initials: D
authors.lastname: Reijnen
authors.affiliation: Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands;
authors.forename: Ellen
authors.initials: E
authors.lastname: Simons
authors.affiliation: Department of General Instrumentation, Faculty of Sciences, Radboud University, Nijmegen, The Netherlands.
authors.forename: Jelle
authors.initials: J
authors.lastname: Eygensteyn
authors.affiliation: Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands;
authors.forename: Leo
authors.identifier: http://orcid.org/0000-0001-5424-4404
authors.initials: L
authors.lastname: Monnens
authors.affiliation: Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands;
authors.forename: René J M
authors.initials: RJ
authors.lastname: Bindels
authors.affiliation: Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands; joost.hoenderop@radboudumc.nl.
authors.forename: Joost G J
authors.initials: JG
authors.lastname: Hoenderop
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D041981:Gastrointestinal Tract / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008810:Mice, Inbred C57BL; D050053:TRPM Cation Channels / Q000378:metabolism; D050916:TRPV Cation Channels / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D050053:TRPM Cation Channels; C459082:TRPM6 protein, human; D050916:TRPV Cation Channels; C422827:TRPV6 protein, human; C530168:Trpm6 protein, mouse; C446923:Trpv6 protein, mouse; D008274:Magnesium; D002118:Calcium
keywords: TRPM6; TRPV6; intestinal absorption; local absorption; stable magnesium isotopes