title: Mechanism and regulation of intestinal phosphate absorption.
abstract: Proper absorption of inorganic phosphate (Pi) from the lumen of the small intestine is of great importance for the achievement of Pi homeostasis. Although due to intralumenal H+ and Pi concentrations, Pi probably can be absorbed as H2PO4- by passive means in the duodenum, transepithelial transport of HPO4(2)- requires uptake from the lumen by an active transport system. The latter has been identified in many species as a Na(+)-Pi cotransport system at the brush-border membrane of the enterocyte. Although it is still a matter of debate whether the intestinal Na+ gradient-driven Pi transport system is electrogenic or electroneutral, there is agreement that the transporter accepts H2PO4- and HPO4(2)- alike. Recently, two laboratories independently isolated a Na(+)-Pi-binding protein which has been tentatively identified as part of the Na(+)-Pi cotransport system. Movement of Pi from the cytosol across the basolateral membrane into the interstitial space has only been preliminarily characterized as transfer by facilitated diffusion. Na(+)-Pi cotransport across the brush-border membrane is under control by the active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). The sterol increases the intrinsic activity, i.e. the number and/or mobility of Na(+)-Pi carriers through genomic and probably also nongenomic actions. In addition, the rate of Na(+)-gradient-driven Pi transport can be enhanced by the hormone also through reduction of transmembrane Na+ fluxes so that more energy for translocation becomes available from the transmembrane Na+ gradient. Evidence is accumulating that thyroid hormones as well as glucocorticoids, apart from stimulating vitamin D-independent Pi uptake, potentiate the effect of 1,25-(OH)2D3 on Na(+)-Pi cotransport across the brush-border membrane.
authors: Department of General and Experimental Pathology, University of Vienna Medical School, Austria.
authors: H S
authors: HS
authors: Cross
authors: H
authors: H
authors: Debiec
authors: M
authors: M
authors: Peterlik
mesh_terms: D000818:Animals; D004032:Diet; D006728:Hormones / Q000494:pharmacology; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000648:ultrastructure; D008871:Microvilli / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*
chemical_list: D006728:Hormones; D010710:Phosphates