Defective Uptake of Basic Amino Acids and l-Cystine by Intestinal Mucosa of Patients with Cystinuria *

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Abstract
A total of 106 mucosal biopsies from the distal duodenum of 2 patients with cystinuria and 11 non- cystinuric controls were incubated with a variety of labeled free amino acid. The incubating fluid was buffered to pH 7.4 and contained L-arginine-Cl4, L-lysine-C14, DL-ornithine-C14, L-cystine-s35; DL-leucine-C14, or L-phenylalanine-C14, final concentration 10-4 [image], 40,000-400,000 cpm. The ability of duodenal mucosa to take up labeled amino acids is best illustrated by the radioactivity present/Unit volume tissue water (I) relative to that contained in a similar volume of final (30 minutes) incubating fluid (O). For each of the labeled amino acids used, the average I/O rations of duodenal mucosa from non-cystinuric subjects ranged between 4.7 and 11.7. Similar values for I/O were obtained when duodenal mucosa from cystinuric subjects was incubated with DL-leucine-C14 and L-phenylalanine-C14. In contrast, the average radioactivity ratios(I/0) for L-cystine-s35 and Cl4 labeled basic amino acids by duodenal mucosa from cystinuric patients was uniformly less than 1.0. Quite comparable values were obtained when normal mucosa was incubated in the presence of KCN, 10-4 M. These experiments demonstrate the presence of a selective defecf of intra-cellular amino acid accumulation by intestinal mucosa of patients with cystinuria. They also indicate that intestinal epithelial cells from normal human subjects may accumulate arginine, lysine, cystine, ornithine, leucine, and phenylalanine against a concentration gradient.