Constitutive expression of the taurine transporter in a human colon carcinoma cell line.
The human colon carcinoma cell line HT-29, when grown to confluence, was found to take up taurine and accumulate it against a concentration gradient from a NaCl-containing uptake medium. Replacement of NaCl with choline chloride almost totally abolished the uptake. Taurine uptake was dependent not only on Na+ but also on Cl-, because other anions failed to support the uptake in the presence of Na+. The uptake process was specific for beta-amino acids such as taurine, hypotaurine, and beta-alanine. Apparently, a single transport system with a Michaelis-Menten constant of 10.6 +/- 0.3 microM was responsible for the uptake. Stoichiometric analyses revealed that the Na+:taurine coupling ratio was 2:1, whereas the Cl-:taurine coupling ratio was 1:1. Culture of the cells in the presence of taurine caused downregulation of the uptake system. These cells were also capable of accumulating beta-alanine against a concentration gradient in the presence of NaCl. Beta-Alanine uptake occurred via a single transport system with an apparent Michaelis-Menten constant of 36 +/- 2 microM. Taurine and beta-alanine exhibited mutual interaction during uptake. Kinetic experiments strongly suggested that a common transporter was responsible for the uptake of these two beta-amino acids. It is concluded that the HT-29 cells constitutively express the taurine transporter and that this cell line may be a suitable model for investigations of intestinal taurine transporter.
Tiruppathi
C
C
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
Brandsch
M
M
Miyamoto
Y
Y
Ganapathy
V
V
Leibach
F H
FH
D000409:Alanine / Q000493:pharmacokinetics; D001692:Biological Transport; D002277:Carcinoma / Q000378:metabolism* / Q000473:pathology; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D003470:Culture Media; D004347:Drug Interactions; D006801:Humans; D007700:Kinetics; D008433:Mathematics; D012964:Sodium / Q000494:pharmacology; D013379:Substrate Specificity; D013654:Taurine / Q000493:pharmacokinetics*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D002712:Chlorides; D003470:Culture Media; D013654:Taurine; D012964:Sodium; D000409:Alanine