Interactions between monosaccharides and leucine in basolateral membrane of isolated chick intestinal epithelial cells.

The characteristics of the interactions between 3-O-methyl-glucose (3-OMG) and monosaccharides or leucine transport were examined on chick isolated intestinal epithelial cells. In a Na+-medium, the unidirectional influx of 1.5 mM 3-OMG was found to be already inhibited by 37.5 mM glucose and 37.5 mM leucine after 20 s incubation. In Na+-free mannitol substituted medium, either glucose, galactose or leucine (37.5 mM) inhibited the unidirectional influx of 3-OMG. Theophylline, a drug that decreases the basolateral permeability to sugars, decreased the unidirectional influx of 1.25 mM leucine in Na+-free medium but increased the steady-state uptake of the aminoacid in Na+-medium. The efflux of 3-OMG from preloaded cells into a Na+-free medium was stimulated by extracellular galactose and leucine (37.5 mM). This was inhibited by theophylline. Our results indicate that sugars and leucine interactions at the Na+-independent transport system could be produced by mutual competition for binding the same system.