Amino acid transport across the hen colon: interactions between leucine and lysine.

Several neutral amino acids such as leucine added on the mucosal side stimulate the mucosal-to-serosal flux (Jm----s) of cationic amino acids such as lysine. We show here in the colon of the NaCl-loaded hen that this is a result of interactions at the basolateral membrane. The hen colon was used because it tolerates prolonged incubation and has a relatively short tip of villus-to-muscularis mucosa distance. Two models have been proposed for the interpretation of the effect of mucosal-side addition of leucine on Jm----s of lysine: 1) one of an allosteric effect of cytoplasmic leucine on lysine efflux across the basolateral membrane; and 2) one of asymmetric heteroexchange of leucine from outside the basolateral membrane for cytoplasmic lysine. These two models were tested by measurements of influx across the brush-border membrane, of Jm----s and serosal-to-mucosal flux, and of steady state epithelial uptake of leucine and lysine. The data favor the model of allosteric interaction and are inconsistent with the model of asymmetric heteroexchange.