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Intestinal glucose absorption is mediated by SGLT1 whereas GLUT2 is considered to provide basolateral exit. Recently, it was proposed that GLUT2 can be recruited into the apical membrane after a high luminal glucose bolus allowing bulk absorption of glucose by facilitated diffusion. Moreover, SGLT1 and GLUT2 are suggested to play an important role in intestinal glucose sensing and incretin secretion. In mice that lack either SGLT1 or GLUT2 we re-assessed the role of these transporters in intestinal glucose uptake after radiotracer glucose gavage and performed Western blot analysis for transporter abundance in apical membrane fractions in a comparative approach. Moreover, we examined the contribution of these transporters to glucose-induced changes in plasma GIP, GLP-1 and insulin levels. In mice lacking SGLT1, tissue retention of tracer glucose was drastically reduced throughout the entire small intestine whereas GLUT2-deficient animals exhibited higher tracer contents in tissue samples than wild type animals. Deletion of SGLT1 resulted also in reduced blood glucose elevations and abolished GIP and GLP-1 secretion in response to glucose. In mice lacking GLUT2, glucose-induced insulin but not incretin secretion was impaired. Western blot analysis revealed unchanged protein levels of SGLT1 after glucose gavage. GLUT2 detected in apical membrane fractions mainly resulted from contamination with basolateral membranes but did not change in density after glucose administration. SGLT1 is unequivocally the prime intestinal glucose transporter even at high luminal glucose concentrations. Moreover, SGLT1 mediates glucose-induced incretin secretion. Our studies do not provide evidence for GLUT2 playing any role in either apical glucose influx or incretin secretion.
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... These dipeptides may be absorbed more promptly than protein-bound amino acids, since they do not have to go through any further digestion [11]. It is identified that transporters of cationic amino acid (CAT1 and CAT2) and peptide (PepT1 and PepT2) in the intestinal epithelium are associated with the capacity of nutrient absorption [2,[12][13][14]. Moreover, estimating phytase activity in fermented SBM, which reflects the efficiency of phosphorus ileal digestibility in broiler chickens, necessitates more exploring. ...
... During the 1st week of age, the room temperature was primarily adjusted to 33 • C and then gradually declined until reaching 21 ± 1 • C, and humidity was kept around 60% during the whole experimental period; also the stocking density was 10 birds/M 2 . The experimental diets were formulated as three stages: starter (d 1-10), grower (d [11][12][13][14][15][16][17][18][19][20][21][22][23][24] and finisher (d [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], with nutrients that cover the requirements of Ross broiler nutritional specification of ROSS [25]. Clean water and feed were allowed all the time. ...
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... During the 1st week of age, the room temperature was primarily adjusted to 33 • C and then gradually declined until reaching 21 ± 1 • C, and humidity was kept around 60% during the whole experimental period; also the stocking density was 10 birds/M 2 . The experimental diets were formulated as three stages: starter (d 1-10), grower (d [11][12][13][14][15][16][17][18][19][20][21][22][23][24] and finisher (d [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], with nutrients that cover the requirements of Ross broiler nutritional specification of ROSS [25]. Clean water and feed were allowed all the time. ...
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Chapter
Facilitative glucose transport is mediated by members of the Glut protein family that belong to a much larger superfamily of 12 transmembrane segment transporters. Six members of the Glut family have been described thus far. These proteins are expressed in a tissue- and cell-specific manner and exhibit distinct kinetic and regulatory properties that reflect their specific functional roles. Glut1 is a widely expressed isoform that provides many cells with their basal glucose requirement. It also plays a special role in transporting glucose across epithelial and endothelial barrier tissues. Glut2 is a high-K m isoform expressed in hepatocytes, pancreatic β cells, and the basolateral membranes of intestinal and renal epithelial cells. It acts as a high-capacity transport system to allow the uninhibited (non-rate-limiting) flux of glucose into or out of these cell types. Glut3 is a low-K m isoform responsible for glucose uptake into neurons. Glut4 is expressed exclusively in the insulin-sensitive tissues, fat and muscle. It is responsible for increased glucose disposal in these tissues in the postprandial state and is important in whole-body glucose homeostasis. Glut5 is a fructose transporter that is abundant in spermatozoa and the apical membrane of intestinal cells. Glut7 is the transporter present in the endoplasmic reticulum membrane that allows the flux of free glucose out of the lumen of this organelle after the action of glucose-6-phosphatase on glucose 6-phosphate. This review summarizes recent advances concerning the structure, function, and regulation of the Glut proteins.
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