Characteristics of L-glutamine transport during Caco-2 cell differentiation

Abstract

Glutamine is the main fuel of intestinal epithelial cells, as well as a precursor for the intense nucleotide biosynthesis which arises with the rapid turnover of enterocytes. In order to determine whether glutamine uptake may vary as a function of metabolic demand, glutamine transport across the brush-border membrane of differentiating Caco-2 cells has been investigated. The uptake of L-[3H]glutamine was measured between day 7 and day 21 post-seeding. Kinetic analysis with glutamine concentrations ranging from 6.25 μM to 12.8 mM revealed the involvement of high affinity Na+-dependent (Kt=110 μM) and low affinity Na+-independent (Kt=900 μM) transport components at day 7. Both components were partially inhibited by L-lysine in a competitive fashion, suggesting that four different systems were responsible for glutamine uptake: B0, B0,+, b0,+ and L. All four systems were present during the differentiation process, with systems L and B0 being responsible for up to 80% of glutamine uptake. Caco-2 cell differentiation was associated with a marked decrease in L-glutamine uptake, which affected both the Na+-dependent and the Na+-independent components. In contrast to glucose uptake, the development of L-glutamine uptake across the brush-border membrane of Caco-2 cells may reflect an adjustment to cell metabolic demand rather than the progressive appearance of a vectorial transport process.