Expression of Na⁺/glucose co-transporter 1 (SGLT1) in the intestine of piglets weaned to different concentrations of dietary carbohydrate

Abstract

Na þ /glucose co-transporter 1 (SGLT1) transports dietary sugars from the lumen of the intestine into enterocytes. Regulation of this protein is essential for the provision of glucose to the body and, thus, is important for maintenance of glucose homeostasis. We have assessed expression of SGLT1 at mRNA, protein and functional levels in the intestinal tissue of 28 d old piglets weaned onto isoenergetic diets with differing concentrations of digestible carbohydrate (CHO). We show that expression of SGLT1 remains constant when piglets are fed up to 40 % CHOcontaining diets. However, there is a significant increase in SGLT1 expression when the CHO content of the diet is . 50 %. Morphometric analyses indicate that the increased expression is not due to a trophic effect. It has been proposed that in rat intestine, in response to a high-CHO diet, GLUT2 (the classical basolateral membrane monosaccharide transporter) is translocated to the luminal membrane of enterocytes to absorb excess dietary glucose. We show, using immunohistochemistry and Western blotting with antibodies raised to amino acids in different epitopes of GLUT2, that under all dietary conditions, low to high CHO, GLUT2 is expressed on the basolateral membrane of pig enterocytes. Furthermore, functional studies indicate that there is no uptake of 2-deoxy-D-glucopyranoside, a specific substrate of Na þ -independent glucose transporters into brush-border membrane vesicles isolated from the intestines of piglets either maintained on low-or high-CHO diets. Thus, SGLT1 is the major route for absorption of dietary sugars across the luminal membrane of swine enterocytes.Na 1 /glucose co-transporter 1: GLUT2: Dietary carbohydrates: Weaned pigletsThe classical model of intestinal sugar transport is that glucose and galactose are transported from the lumen of the intestine into enterocytes by the Na þ /glucose co-transporter 1 (SGLT1), whereas fructose is transported by a facilitated, Na-independent transporter, GLUT5. Glucose, galactose and fructose, once accumulated in the cells, are released from the cytosol across the basolateral membrane into the systemic system by another facilitated Na þ -independent monosaccharide transporter, GLUT2 (1,2) .It has been suggested, however, that in the intestine of rodents, in response to a high-carbohydrate (CHO) diet, or intestinal infusion with high concentrations of glucose or fructose, GLUT2 is translocated to the luminal membrane of enterocytes to absorb dietary glucose or fructose (3,4) , implying that GLUT2, as well as SGLT1, is involved in the uptake of dietary sugars. In support of this proposition Gouyon et al. (5) have reported that in GLUT2-knockout mice, fructose uptake in the intestinal brush-border membrane vesicles (BBMV) was half of that in the wild-type mice, indicating that brush-border membrane GLUT2 absorbs 50 % of luminal fructose (5) .In contrast, it has been demonstrated by Barone et al. (6) that GLUT5-knockout mice cannot absorb fructose. Furthermore, these workers have shown that the absorption of ...

Kinetics and mechanisms of glucose absorption in the rat small intestine under physiological conditions

“…At the same time, the results of our kinetic studies and mathematical modeling confirm the central role of the secondary active transport mediated by SGLT1 in the absorption of glucose in the small intestine [1,2,31,32]. Only the model, that has been developed on this assumption and takes into account the architecture of the intestinal surface, can satisfactorily reproduce the kinetics of maltose hydrolysis and glucose absorption in a wide range of substrate concentrations.…”

Glucose sensing and signalling; regulation of intestinal glucose transport

“…These monosaccharides, when accumulated in the enterocytes, exit the cell across the basolateral membrane into the systemic system by another Na + -independent monosaccharide transporter, GLUT2; a bidirectional transporter that can move glucose out or into the cell depending on its concentration gradient (6) . SGLT1 has been shown to be expressed on the brush-border membrane of villus enterocytes in most mammalian species studied (20)(21)(22)(23)(24)(25) . In general, expression levels are higher in jejunum >duodenum > ileum.…”

Sodium/glucose cotransporter-1, sweet receptor, and disaccharidase expression in the intestine of the domestic dog and cat: two species of different dietary habit

“…Western blot analysis. The abundance of SGLT1 protein in cellular homogenates and BBMV was determined by Western blotting, as described previously (31). Protein components of BBMV were separated by SDS-PAGE on 8% (wt/vol) polyacrylamide minigels, containing 0.1% (wt/vol) SDS, and electrotransferred to PVDF membrane.…”

“…The amount of specific fluorescent labeling for SGLT1 was determined as follows and has been published previously (31). Images were captured using IP lab (Nikon).…”

“…While cDNA encoding SGLT1 has been cloned in a number of species, there was no information on sequence of fSGLT1. This knowledge was necessary to assess the suitability of our antibody raised to the peptide STLFTMDIYTKIRKKASEK used successfully to measure SGLT1 expression in BBMV isolated from the intestine of a number of species (13,14,16,17,30,31,39). In cats, this sequence is very similar to other species and is identical to that in the horse.…”