Sugar transport heterogeneity in caco-2 cells: kinetic separation and characterization of three transport modes. Bissonnette, Pierre, H[acute]el[grave]ene Gagn[acute]e, Michael J. Coady, Khadija Benabdallah, Jean-Yves Lapointe, and Alfred Berteloot. Membrane Transport Research Group, Departments of Physiology and Physics, Faculty of Medicine, University of Montreal, CP 6128, succursale "Centre-Ville", Montreal (Qu[acute]ebec) Canada H3C 3J7, Phone: (514)-343-5634, Fax: (514)-343-2111
APStracts 2:0240G, 1995.
The question of sugar transport heterogeneity in the human intestinal Caco-2 cell line was addressed using [alpha]-methyl-D-glucose (AMG) and 2-deoxy-D-glucose (DG) as substrate analogues for D-glucose, the transport inhibitors phlorizin (PZ) and phloretin (PT), and NaCl or choline chloride uptake media. The data are compatible with the existence of three distinct pathways that can be isolated kinetically according to specific characteristics: i) a "AMG-strict" system, strictly Na+-dependent and specific for AMG (Km = 2.0 +/- 0.3 mM) but sensitive to both PZ and PT, with PZ being more potent than PT; ii) a "DG-strict" system, strictly Na+-independent and specific for both DG (Km = 5.2 +/- 0.5 mM) and PT; and iii) a "DG/AMG-mixed" system, strictly Na+-dependent, with loose specificities for the glucalogues DG (Km = 0.81 +/- 0.07 mM) and AMG (Km = 8.1 +/- 0.8 mM), and the inhibitors PZ and PT, but with PT being more potent than PZ. Since SGLT1 obtained by PCR from either Caco-2 cells or normal human jejunum demonstrated identical transport properties when expressed in Xenopus laevis oocytes, we conclude that the "AMG-strict" system represents the expression of human SGLT1 activity in this cell line. Moreover, Western blot analysis revealed that SGLT1 is located exclusively in the apical membrane. In contrast, neither the nature nor the membrane location of both the "DG-strict" and "DG/AMG-mixed" pathways could be resolved unambiguously. Still, it is demonstrated that expression of the latter system is constitutive to all Caco-2 cells and that its Na+-dependence is not the consequence of H+-dependent transport activity. Aside from the presence of the "DG/AMG-mixed" system, a salient feature of Caco-2 cells is that the GLUT3 protein is located exclusively in the brush border membrane. Due to these limitations, it is concluded that the Caco-2 cell line cannot be considered as equivalent to either fetal colonic cells or normal enterocytes. 

Received 16 May 1995; accepted in final form 7 November 1995.
APS Manuscript Number G206-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95