CHLORIDE-DEPENDENT AMINO-ACID-TRANSPORT IN THE HUMAN SMALL-INTESTINE

Carriers of beta amino acids and imino acids in the small intestine of rabbits and guinea pigs are chloride dependent, and a cotransport of chloride, sodium, and 2-methyl-aminoisobutyric acid has been shown. Th is study examines the chloride dependence of amino acid transport in t he human small intestine. The steady state tissue uptake of amino acid s, given as the ratio between substrate concentration in intracellular and extracellular water after 35 minutes incubation at 37 degrees C, was determined in mucosal biopsy specimens from the duodenum of patien ts undergoing diagnostic upper endoscopy and compared using one way an alysis of variance. Uptake of leucine and alpha-methyl-D-glucoside in the duodenum and the distal ileum did not differ. The accumulation of all substrates was sodium dependent. In the absence of mucosal chlorid e the uptake of taurine, glycine, and 2-methyl-aminoisobutyric acid wa s significantly reduced while that of leucine and alpha-methyl-D-gluco side was unaffected and the reduction of beta alanine uptake not stati stically significant. Uptake of 2-methyl-aminoisobutyric acid and prol ine showed mutual inhibition. Leucine did not reduce uptake of the bet a amino acids. In conclusion, chloride dependent transport processes f or 2-methyl-aminoisobutyric acid, taurine, and glycine are present in the human small intestine.