Effect of N^ε-dansyl-L-lysine [N^ε-(5-dimethylaminonaphthalenesulfonyl)-L-lysine] on amino acid transport across the brush border of isolated rat small intestine was investigated. N^ε-Dansy-L-lysine was not actively accumulated nor transmurally transported by the intestinal tissue; nonetheless, it competitively inhibited the basic amino acid transport with a Ki of about 0.4mM for L-lysine, but entirely not the neutral amino acid transport. The inhibition was relatively independent of extracellular Na⁺ The minimal dependence on Na⁺ parallels with the least Na⁺ dependence of lysine transport among various amino acid transport systems, suggesting the inhibition competes for a step involved in a heteroexchange process mediating the greater portion of lysine transport. The results provided a basis for a potential use of N^ε-dansyl-L-lysine as a fluorescent probe in delineating its interaction with basic amino acid transport system in the small intestine.

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