Exchange transport and amino acid charge as the basis for Na +-independent lysine uptake by isolated intestinal epithelial cells

Abstract

1. 1. The properties of the Na +-independent stimulation of lysine uptake by intracellular alanine in isolated intestinal epithelial cells from the rat were determined and compared to the properties of Na +-independent lysine uptake previously established in order to ascertain whether these two transport processes were related. 2. 2. Dinitrophenol, anaerobiosis and ouabain did not inhibit the Na +-independent stimulation of lysine uptake by alanine while ethacrynic acid, N-ethylmaleimide ATP, arginine and incubation in the cold produced a wide range of inhibitions. These inhibitors similary influencend Na +-independent lysine uptake. 3. 3. Na +-independent, alanine-stimulated lysine uptake was independent of extracellular K + but was decreased 10–17% by the replacement of the Ca 2+ and/or Mg 2+ of the incubation medium thus producing a pattern similar to that observed with Na +-independent lysine uptake. 4. 4. The diverse effects of pH on the stimulation of lysine uptake by alanine-preloaded cells very closely approximated that found for Na +-independent lysine uptake by non-preloaded cells. 5. 5. These results show that the properties of alanine-stimulated lysine uptake are similar to the properties of the Na +-independent uptake of this amino acid, suggesting that both systems are mediated by the same or related transport processes. 6. 6. A study of the relationship between the net positive charge of histidine and the magnitude of Na +-independent histidine uptake revealed that Na +-independent histidine uptake was increased by 17–24% at pH 4.5 where the cationic form of histidine is the primary molecular species. 7. 7. However, alanine-stimulated histidine uptake showed a 40% increase at pH 4.5.