title: Vitamin D-enhanced duodenal calcium transport.
abstract: For humans and rodents, duodenum is a very important site of calcium absorption since it is exposed to ionized calcium released from dietary complexes by gastric acid. Calcium traverses the duodenal epithelium via both transcellular and paracellular pathways in a vitamin D-dependent manner. After binding to the nuclear vitamin D receptor, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] upregulates the expression of several calcium transporter genes, e.g., TRPV5/6, calbindin-D9k, plasma membrane Ca(2+)-ATPase1b, and NCX1, thereby enhancing the transcellular calcium transport. This action has been reported to be under the regulation of parathyroid-kidney-intestinal and bone-kidney-intestinal axes, in which the plasma calcium and fibroblast growth factor-23 act as negative feedback regulators, respectively. 1,25(OH)2D3 also modulates the expression of tight junction-related genes and convective water flow, presumably to increase the paracellular calcium permeability and solvent drag-induced calcium transport. However, vitamin D-independent calcium absorption does exist and plays an important role in calcium homeostasis under certain conditions, particularly in neonatal period, pregnancy, and lactation as well as in naturally vitamin D-impoverished subterranean mammals.
authors.affiliation: Office of Academic Management, Faculty of Allied Health Sciences, Burapha University, Chonburi, Thailand; Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.
authors.forename: Kannikar
authors.initials: K
authors.lastname: Wongdee
authors.affiliation: Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand; Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand. Electronic address: naratt@narattsys.com.
authors.forename: Narattaphol
authors.initials: N
authors.lastname: Charoenphandhu
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology*; D018167:Receptors, Calcitriol / Q000378:metabolism; D014807:Vitamin D / Q000378:metabolism*
chemical_list: D018167:Receptors, Calcitriol; D014807:Vitamin D; D002118:Calcium
keywords: Bone; Calcium absorption; Duodenum; Paracellular transport; Solvent drag; Transcellular transport; Vitamin D