title: In vitro study on the transport of zinc across intestinal epithelial cells using Caco-2 monolayers and isolated rat intestinal membranes.
abstract: The variety of physiologic and biologic functions of zinc is fascinating and could be applicable to medicine. Our previous studies demonstrated that the absorption of zinc after oral administration to rats is dose-dependent. In order to clarify the detailed mechanism of the dose-dependent in vivo absorption, the transport of zinc across intestinal epithelial cells was investigated using Caco-2 monolayers and isolated rat intestinal membranes. The permeation of zinc across Caco-2 monolayers is concentration-dependent, and both saturable and nonsaturable components are involved. The Michaelis constant and maximum transport rate for saturable transport are 11.7 μM and 31.8 pmol min(-1) cm(-2), respectively; the permeability coefficient for nonsaturable trasnport is 2.37×10(-6) cm s(-1). These parameters for permeation across membranes isolated from duodenum, ileum, and jejunum of rats are similar with those of Caco-2 cells. The comparison of the parameters for permeation across isolated intestinal membrane suggests that the major site of intestinal zinc absorption in rats is the duodenum. The maximum rate of zinc transport across the isolated intestinal membrane (V(max)) shows no correlation with mRNA expression of ZIP4, ZIP5 or ZnT1 in rats, but shows an inverse correlation with that of metallothioneins (MTs). This finding may be partly explained by the buffering role of metallothionein in intestinal absorption. The saturable transport of zinc is not simply determined only by the influx transporter, ZIP4, since three influx and efflux transporters are involved in the transport of zinc.
authors.affiliation: Department of Biopharmaceutics, Kyoto Pharmaceutical University, Japan. yasuno-tohru@linical.co.jp
authors.forename: Tohru
authors.initials: T
authors.lastname: Yasuno
authors.forename: Hiroki
authors.initials: H
authors.lastname: Okamoto
authors.forename: Miho
authors.initials: M
authors.lastname: Nagai
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kimura
authors.forename: Takanori
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Kozue
authors.initials: K
authors.lastname: Nagano
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yoshikawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yasui
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Katsumi
authors.forename: Toshiyasu
authors.initials: T
authors.lastname: Sakane
authors.forename: Akira
authors.initials: A
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D027682:Cation Transport Proteins / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D008297:Male; D008668:Metallothionein / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015032:Zinc / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; C491055:Mt2A protein, rat; D008668:Metallothionein; D015032:Zinc