Mechanisms of glucose uptake in intestinal cell lines: Role of GLUT2

Abstract

BACKGROUND GLUT2 is translocated to the apical membrane of enterocytes exposed to glucose concentrations >~50 mM. Mechanisms of GLUT2-mediated glucose uptake in cell culture models of enterocytes have not been studied. AIM To explore mechanism(s) of glucose uptake in three enterocyte-like cell lines. METHODS Glucose uptake was measured in Caco-2, RIE-1, and IEC-6 cell lines using varying concentrations of glucose (0.5–50 mM). Effects of phlorizin (SGLT1 inhibitor), phloretin (GLUT2 inhibitor), nocodazole and cytochalasin B (disrupters of cytoskeleton), calphostin C and chelerythrine (PKC inhibitors), and phorbol 12-myristate 13-acetate (PKC activator) were evaluated. RESULTS Phlorizin inhibited glucose uptake in all three cell lines. Phloretin inhibited glucose uptake in Caco-2 and RIE-1 cells. Starving cells decreased glucose uptake in Caco-2 and RIE-1 cells. Glucose uptake was saturated at ≥10 mM glucose in all three cell lines when exposed briefly (≤ 1 min) to glucose. After exposure for ≥5 min in Caco-2 and RIE-1 cells, glucose uptake did not saturate and Km and Vmax increased. This increase in glucose uptake was inhibited by phloretin, nocodazole, cytochalasin B, calphostin C, and chelerythrine. PMA enhanced glucose uptake by 20%. Inhibitors and PMA had little or no effect in the IEC-6 cells. CONCLUSION Constitutive expression of GLUT2 in the apical membrane along with additional translocation of cytoplasmic GLUT2 to the apical membrane via an intact cytoskeleton and activated PKC appears responsible for enhanced carrier-mediated glucose uptake at greater glucose concentrations (≥20 mM) in Caco-2 and RIE-1 cells. IEC-6 cells do not appear to express functional GLUT2.

Berries and anthocyanins: promising functional food ingredients with postprandial glycaemia-lowering effects

“…This may occur via inhibition of GLUT2 under postprandial glycaemic conditions, since this transporter is believed to be functionally important under conditions of high luminal glucose concentrations (76) . However, inhibition of SLGT1 activity may also play a significant role in berry polyphenolmediated control of glucose homeostasis since SGLT1 is instrumental in the regulation of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 secretion and up-regulation of GLUT2 (92) .…”

Transepithelial glucose transport and Na+/K+ homeostasis in enterocytes: an integrative model

“…SGLT1 has also been shown to be rapidly upregulated by sweet taste receptors (76). In addition, there is evidence for trafficking of GLUT2 to the apical brush border membrane during high luminal glucose concentrations (48,103). This makes GLUT2 a candidate responsible for the nonsaturable component of glucose uptake from the small intestine (36).…”

Acute Enterocyte Adaptation to Luminal Glucose: A Posttranslational Mechanism for Rapid Apical Recruitment of the Transporter GLUT2

“…[26]. Our work in cell culture shows this acute adaptation to occur within 5 min [18]. Given that SGLT1 inhibition (addition of phlorizin) at greater concentrations of luminal glucose also significantly decreases glucose absorption further suggests that GLUT2 activation is dependent on the activity of SGLT1.…”