Lysine transport in lactating rat mammary tissue: evidence for an interaction between cationic and neutral amino acids.

The transport of lysine by the lactating rat mammary gland has been examined to determine whether there is an interaction between cationic and neutral amino acids. Lysine uptake was time dependent and unaffected by replacing Na+ with choline. In the presence of Na+, lysine influx was inhibited by cationic amino acids (arginine, homoarginine, ornithine and lysine) and by a range of neutral amino acids (methionine, glutamine, leucine, phenylalanine, alanine, asparagine, alpha-aminoisobutyric acid (AIB), 2-aminobicyclo [2,2,1] heptane-2-carboxylic acid (BCH), proline and tryptophan). Leucine and glutamine also inhibited lysine influx in the absence of Na+ but phenylalanine and proline did not. Lysine efflux from mammary tissue was trans-accelerated by various cationic amino acids (lysine, arginine, homoarginine and ornithine). In addition, leucine and glutamine were capable of trans-stimulating lysine efflux in the presence and absence of Na+. It appears that cationic and neutral amino acids stimulated lysine efflux at a single locus.