Kinetic analysis of zinc uptake and serosal transfer by vascularly perfused rat intestine

Abstract

Transport kinetics were examined for uptake of 65Zn from the lumen and for transport of mucosal 65Zn subsequent to uptake in the isolated, vascularly perfused intestines of rats fed either a zinc-deficient or zinc-adequate diet. Zinc depletion influenced the intestinal transport of zinc by stimulating a saturable uptake mechanism, reducing secretion of mucosal 65Zn into the lumen, and increasing the rate of 65Zn turnover in a rapidly absorbed mucosal zinc compartment. Uptake of 65Zn involved both saturable and nonsaturable processes. The saturable process was stimulated by zinc depletion with the apparent maximal transport rate for the saturable mechanism increasing from 60 to 180 nmol Zn X g-1 X 30 min-1. Most of the 65Zn taken up was not involved in the short-term secretion or absorption, and mucosal 65Zn retention was independent of dietary zinc status. Absorption of mucosal 65Zn was nonsaturable, involved a rapid exchanging zinc compartment, and was stimulated by zinc depletion. The half-life for 65Zn in this mucosal zinc compartment was approximately 24 min in the zinc-adequate group and 13 min in the zinc-depleted group.

<i>In Vitro</i> Study on the Transport of Zinc across Intestinal Epithelial Cells Using Caco-2 Monolayers and Isolated Rat Intestinal Membranes

“…K m values determined in our study were approximately 10 μM, which are close to those derived from the luminal disappearance in the perfused rat intestine (32 μM) 20) and the uptake by brush-border membrane vesicles (24.1 μM). 21) In the experiments using Caco-2 cells 37) or MDCK cells, 38) K m were 42 μM and 18.9 μM, respectively.…”

“…However, detailed information on the intestinal absorption of zinc is likely insufficient at present. Functional studies on the intestinal absorption of zinc using preparations such as everted rat gut sacs, 15,16) the isolated vascularly perfused rat intestine, [17][18][19][20] and intestinal brush-border membrane vesicles from the small intestine of rats 21) provide evidence of saturable components of zinc transport. In most experiments, zinc absorption was measured indirectly.…”

Regulation of the zinc transporter ZnT-1 by dietary zinc

“…As a highly charged, hydrophilic ion, Zn(II) cannot cross biological membranes by simple diffusion, and specialized mechanisms therefore must exist for its cellular uptake and release. Zinc absorption has been studied extensively in several model systems, particularly perfused intestinal segments (2,3) and isolated intestinal cells (4). Zinc transport has been characterized in many cell types, including fibroblasts (5), hepatocytes (6,7), placental trophoblasts (8), and endothelial cells (9).…”

Differential Adaptations of the Hypothalamus-Pituitary-Thyroid Axis Between Food Restriction and Anorexia

“…Two main protein families are in charge of Zn transport: 1) at least 15 members of the ZIP (i.e., Zn-regulated metal transporter, Iron-regulated metal transporter-like protein) family (Eide, 2004) and 2) ten members of the ZnT (Zn Transporter) family (Liuzzi & Cousins, 2004). Absorption rate is able to adjust to Zn availability, i.e., there is an increase on the maximum Zn absorption rate in rat enterocytes cell cultures, following a reduction on dietary Zn (Hoadley et al, 1987), just as there is an increase on transepithelial Zn flux on CACO-2 cells after treatment with 5 µM when compared to one of 25 µM Zn (Reeves et al, 2001). …”