Effect of pH on l- and d-methionine uptake across the apical membrane of Caco-2 cells

Abstract

The transport systems involved in intestinal methionine (Met) absorption are described as Na ϩ -dependent and Na ϩ -independent mechanisms. However, since recent studies have suggested the importance of the H ϩ gradient as a driving force for intestinal nutrient absorption, the aim of the present work was to test whether Met transport across the apical membrane of Caco-2 cells is affected by extracellular pH. The results show that Land D-Met uptake was increased by lowering extracellular pH from 7.4 to 5.5, in both the presence and absence of Na ϩ . Cis-inhibition experiments revealed that inhibition of L-Met transport by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) or L-lysine (L-Lys) was higher at a pH of 5.5. Moreover, the BCH-insensitive component was not affected by pH, whereas the L-Lys-insensitive component was increased by lowering extracellular pH, thus suggesting the participation of system L. The contribution of another mechanism, sensitive to both BCH and L-Lys, was also considered. The inhibition obtained with taurine (Tau) was also higher at a pH of 5.5, thus suggesting the involvement of system B 0,ϩ on pH-stimulated component. As for D-Met uptake, the results showed higher inhibition with L-Lys and Tau at a pH of 5.5 and no effect on the L-Lys-or Tau-insensitive component. In conclusion, Met transport across the apical membrane of Caco-2 cells is increased by low extracellular pH as the result of the stimulation of two transport systems functionally identified with systems L and B 0,ϩ for L-Met and with system B 0,ϩ for D-Met.

Taurine transporter gene expression in peripheral mononuclear blood cells of type 2 diabetic patients

“…Previous data on plasma methionine are scarce and one paper (Tessari et al 2005) shows that it is not changed in diabetic patients, while we found a significant increase in methionine. However, considering that taurine inhibits methionine uptake in some cell models such as intestinal Caco-2 cells (Martin-Venegas et al 2009) the observed increase in methionine could be biologically plausible.…”

In vitro intestinal absorption of amino acid mixtures extracted from codfish (Gadus morhua L.) salting wastewater

“…Absorption of an amino acid depends on concentration, character and side chain as well as on the presence of other amino acids (Chakrabarti, ; Frenhani & Burini, ; Bröer, ; El‐Kattan & Varma, ). Assuming as a reference the normal concentration in the intestinal lumen, amino acids with short side chain, such as glycine and taurine, are slowly transported when in lower concentration and vice versa ; amino acids with lipophilic side chain, such as methionine, phenylalanine and tryptophan, are rapidly transported when in lower concentration and vice versa ; acidic amino acids, such as aspartic acid and glutamic acid, are rapidly transported when in higher concentration and vice versa ; dibasic amino acids, such lysine and arginine, are always slowly transported (Martín‐Venega et al ., ).…”

Gastrointestinal methionine shuttle: Priority handling of precious goods

“…On the other hand, intracellular l ‐Met inhibits l ‐arginine efflux and this results in a stimulation of net l ‐arginine uptake , confirming a previous study demonstrating that l ‐Met and l ‐citrulline stimulate l ‐arginine uptake . Taurine supplementation has also been suggested to reduce Met absorption , and this was used to explain the reduced Met and homocysteine levels in the blood of rabbits fed an atherogenic diet supplemented with taurine .…”