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 ex amined to determine whether there is an interaction between cationic a nd neutral amino acids. Lysine uptake was time dependent and unaffecte d by replacing Na+ with choline. In the presence of Na+, lysine influx was inhibited by cationic amino acids (arginine, homoarginine, ornith ine and lysine) and by a range of neutral amino acids (methionine, glu tamine, leucine, phenylalanine, alanine, asparagine, alpha-aminoisobut yric acid (AIB), 2-aminobicyclo [2,2,1] heptane-2-carboxylic acid (BCH ), proline and tryptophan). Leucine and glutamine also inhibited lysin e influx in the absence of Na+ but phenylalanine and proline did not. Lysine efflux from mammary tissue was trans-accelerated by various cat ionic amino acids (lysine, arginine, homoarginine and ornithine). In a ddition, leucine and glutamine were capable of trans-stimulating lysin e efflux in the presence and absence of Na+. It appears that cationic and neutral amino acids stimulated lysine efflux at a single locus.