Evidence for an interaction between cationic and neutral amino acids at the blood-facing aspect of the lactating rat mammary epithelium.

The transport of lysine by perfused lactating rat mammary tissue has been examined using a rapid, paired-tracer dilution technique. This experimental approach allowed the characteristics of lysine transport across the blood-facing aspect of the mammary epithelium to be studied. The clearance of lysine from the perfusate was influenced by the extracellular lysine concentration in a fashion consistent with the presence of carrier-mediated transport. Replacing extracellular Na+ with N-methyl-D-glucamine had no significant effect on lysine transport. Lysine uptake was inhibited by extracellular leucine and glutamine but not by alpha-(methylamino)isobutyric acid. Leucine interacted with lysine transport under Na+(-)free conditions. It appears that the system for cationic acid transport which is situated in the blood-facing aspect of the lactating rat mammary epithelium may also accept neutral amino acids as substrates.