Quercetin-3-Glucoside Is Transported by the Glucose Carrier SGLT1 across the Brush Border Membrane of Rat Small Intestine

In the present study we investigated a possible involvement of the intestinal sodium-dependent glucose transporter (SGLT)1 in the absorption of quercetin-3-glucoside (Q3G). Pieces of rat jejunum or proximal colon were mounted in Ussing-type chambers and incubated under short-circuited conditions. Test flavonols were added to the mucosal or serosal bathing solution (initial concentration, 100 μmol/L) and disappearance from the donor compartment was monitored for 2 h. With jejunal tissue, only 13.6 ± 3.5% of the initial dose of Q3G was found in the mucosal compartment 2 h after mucosal addition. Simultaneous addition of D-glucose (10 mmol/L) significantly reduced the disappearance of Q3G (remaining concentration, 33.4 ± 6.9%) as did a Na+-free buffer solution containing phloridzin (final mucosal concentration of Q3G, 54.2 ± 7.7%). In these experiments, disappearance of Q3G was paralleled by the appearance of quercetin in the mucosal solutions. In contrast, D-fructose (10 mmol/L) did not influence the disappearance of Q3G (Na+-free conditions). With proximal colon, 78.2 ± 11.5% of the initial concentration of Q3G was still present in the mucosal solution after 2 h. When added to the serosal side, the concentration of Q3G decreased only slightly (jejunum, 96.1 ± 2.1%; proximal colon, 90.7 ± 1.2%). The concentration of rutin did not change after mucosal or serosal addition. Neither transport of intact glycosides nor of free quercetin from the donor into the acceptor compartment was observed under our experimental conditions. Taken together, the results clearly indicate a role of SGLT1 in mucosal uptake of the Q3G.