title: Na+-independent phosphate transport in Caco2BBE cells.
abstract: Pi transport in epithelia has both Na(+)-dependent and Na(+)-independent components, but so far only Na(+)-dependent transporters have been characterized in detail and molecularly identified. Consequently, in the present study, we initiated the characterization and analysis of intestinal Na(+)-independent Pi transport using an in vitro model, Caco2BBE cells. Only Na(+)-independent Pi uptake was observed in these cells, and Pi uptake was dramatically increased when cells were incubated in high-Pi DMEM (4 mM) from 1 day to several days. No response to low-Pi medium was observed. The increased Pi transport was mainly caused by Vmax changes, and it was prevented by actinomycin D and cycloheximide. Pi transport in cells grown in 1 mM Pi (basal DMEM) decreased at pH > 7.5, and it was inhibited with proton ionophores. Pi transport in cells incubated with 4 mM Pi increased with alkaline pH, suggesting a preference for divalent phosphate. Pi uptake in cells in 1 mM Pi was completely inhibited only by Pi and partially inhibited by phosphonoformate, oxalate, DIDS, SITS, SO4 (2-), HCO3 (-), and arsenate. This inhibition pattern suggests that more than one Pi transporter is active in cells maintained with 1 mM Pi. Phosphate transport from cells maintained at 4 mM Pi was only partially inhibited by phosphonoformate, oxalate, and arsenate. Attempts to identify the responsible transporters showed that multifunctional anion exchangers of the Slc26 family as well as members of Slc17, Slc20, and Slc37 and the Pi exporter xenotropic and polytropic retrovirus receptor 1 are not involved.
authors.affiliation: Department of Toxicology, University of Zaragoza, Zaragoza, Spain; and.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Candeal
authors.affiliation: Department of Toxicology, University of Zaragoza, Zaragoza, Spain; and Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Denver, Aurora, Colorado.
authors.forename: Yupanqui A
authors.initials: YA
authors.lastname: Caldas
authors.affiliation: Department of Toxicology, University of Zaragoza, Zaragoza, Spain; and.
authors.forename: Natalia
authors.initials: N
authors.lastname: Guillén
authors.affiliation: Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Denver, Aurora, Colorado.
authors.forename: Moshe
authors.initials: M
authors.lastname: Levi
authors.affiliation: Department of Toxicology, University of Zaragoza, Zaragoza, Spain; and sorribas@unizar.es.
authors.forename: Víctor
authors.identifier: http://orcid.org/0000-0003-3457-323X
authors.initials: V
authors.lastname: Sorribas
mesh_terms: D000818:Animals; D001692:Biological Transport; D018938:Caco-2 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D007700:Kinetics; D008297:Male; D049990:Membrane Transport Modulators / Q000494:pharmacology; D028061:Phosphate Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D017208:Rats, Wistar
chemical_list: D049990:Membrane Transport Modulators; D028061:Phosphate Transport Proteins; D010710:Phosphates
keywords: Caco2BBE cells; Na+-independent Pi uptake; inorganic phosphate; phosphate absorption; phosphate transport; small intestine