5-aminolaevulinic acid methyl ester transport on amino acid carriers in a human colon adenocarcinoma cell line

The transport mechanisms of 5-aminolevulinic acid methyl ester (5-ALA-ME) h ave been studied in a human adenocarcinoma cell line (WiDr) by means of (14 )[C]-labeled 5-ALA-ME. The transport was found to be partly Na+ dependent, while the extracellular Cl- concentration did not affect the uptake, The tr ansport of 5-ALA-ME into WiDr cells was dependent on the incubation tempera ture and was found to be completely blocked by the inhibitors of energy met abolism, 2-deoxyglucose and sodium azide, WiDr cells were treated with 10 m M of 14 different amino acids and the substrate specificity of the 5-ALA-ME transporter(s) was analyzed by treating the cells with 23 muM or 1 mM (14) [C]-labeled 5-ALA-ME. The transport of 5-ALA-ME was found to be inhibited t o the highest extent, Le. about 60%, by the nonpolar amino acids L-alanine, L-methionine, L-tryptophan and glycine, The uptake of 5-ALA-ME followed an exponential decay with increasing concentration of glycine, reaching a max imum inhibition of uptake of 5-ALA-ME of 55%, Sarcosine, a specific inhibit or of system Gly, did not significantly inhibit 5-ALA-ME transport. In cont rast to transport of 5-ALA, 5-ALA-ME does not seem to be taken up by system BETA transporters. In conclusion, the cellular uptake of 5-ALA-ME into WiD r cells seems to be due to active transport mechanisms, involving transport ers of nonpolar amino acids.