Effect of pH on L- and D-methionine uptake across the apical membrane of Caco-2 cells.
The transport systems involved in intestinal methionine (Met) absorption are described as Na(+)-dependent and Na(+)-independent mechanisms. However, since recent studies have suggested the importance of the H(+) 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 l- and d-Met uptake was increased by lowering extracellular pH from 7.4 to 5.5, in both the presence and absence of Na(+). 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,+) 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,+) for l-Met and with system B(0,+) for d-Met.
Martín-Venegas
Raquel
R
Departament de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Av. Joan XXIII s/n, 08028 Barcelona, Spain.
Rodríguez-Lagunas
M José
MJ
Mercier
Yves
Y
Geraert
Pierre-André
PA
Ferrer
Ruth
R
D027062:Amino Acid Transport System L / Q000378:metabolism; D026905:Amino Acid Transport Systems / Q000378:metabolism*; D026923:Amino Acid Transport Systems, Basic / Q000378:metabolism; D000598:Amino Acids, Cyclic / Q000378:metabolism; D001692:Biological Transport; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D008715:Methionine / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013237:Stereoisomerism; D013654:Taurine / Q000378:metabolism
D027062:Amino Acid Transport System L; D026905:Amino Acid Transport Systems; D026923:Amino Acid Transport Systems, Basic; D000598:Amino Acids, Cyclic; D013654:Taurine; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D012964:Sodium; D008715:Methionine; D008239:Lysine