L-type amino acid transporters in two intestinal epithelial cell lines function as exchangers with neutral amino acids.
The present study examined the functional characteristics of the inward [(14)C]-L-leucine transporter in two intestinal epithelial cell lines (human Caco-2 and rat IEC-6). The uptake of [(14)C]-L-leucine was largely promoted through an energy-dependent and sodium-insensitive transporter, although a minor component of [(14)C]-L-leucine uptake ( approximately 15%) required extracellular sodium. [(14)C] -L-leucine uptake was insensitive to N-(methylamino)-isobutyric acid, but competitively inhibited by 2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid (BCH). Both L- and D-neutral amino acids, but not acidic and basic amino acids, markedly inhibited [(14)C]-L-leucine accumulation. The efflux of [(14)C]-L-leucine was markedly increased (P < 0.05) by L-leucine and BCH, but not by L-arginine. In IEC-6 cells, but not in Caco-2 cells, the uptake of [(14)C]-L-leucine at acidic pH (5.0 and 5.4) was greater (P < 0.05) than at pH 7.4. In conclusion, it is likely that system B(0) might be responsible for the sodium-dependent uptake of L-leucine in Caco-2 and IEC-6 cells, whereas sodium-independent uptake of L-leucine may include system LAT1, whose activation results in transstimulation of L-leucine outward transfer.
Fraga
S
S
Institute of Pharmacology & Therapeutics, Faculty of Medicine, 4200-319 Porto, Portugal.
Serrão
M P
MP
Soares-da-Silva
Patricio
P
D027062:Amino Acid Transport System L / Q000502:physiology*; D021542:Amino Acids, Neutral / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D018938:Caco-2 Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007930:Leucine / Q000493:pharmacokinetics*; D051381:Rats; D013045:Species Specificity
D027062:Amino Acid Transport System L; D021542:Amino Acids, Neutral; D007930:Leucine