INTERACTIONS BETWEEN LEUCINE AND LYSINE TRANSPORT IN RABBIT ILEUM

1. 1. The presence of 2 mM leucine in the mucosal solution markedly stimulates the rate of net lysine transport across short-circuited segments of rabbit ileum. This stimulatory effect is due entirely to an increase in the unidirectional flux of lysine from mucosa to serosa; the flux from serosa to mucosa is unaffected by leucine. 2. 2. High concentrations of lysine inhibit lycine transport across the brush border, and high concentrations of leucine similarly inhibit lysine transport. These observations suggest that the processes mediating the transport of these two amino acids across the brush border have overlapping specificities. 3. 3. The stimulatory effect of leucine on lysine transport is due, primarily, to an increase in the unidirectional flux of lysine out of the cell across the serosal and/or lateral membranes. The phenomenon cannot be readily explained in terms of known carrier models and suggests a direct noncompetitive interaction between leucine and a carrier mechanism responsible for lysine movement across the serosal boundary of the epithelium. 4. 4. Preloading the intestinal tissue with leucine alone markedly enhances the unidirectional influx of lysine from the mucosal solution across the brush border. Since preloading with lysine has no effect on lysine influx and preloading with leucine has no effect on leucine influx, this phenomenon appears to be another indication of an effect of leucine on the lysine transport mechanism. © 1969.