BETA-AMINO ACID TRANSPORT IN PIG SMALL-INTESTINE IN-VITRO BY A HIGH-AFFINITY, CHLORIDE-DEPENDENT CARRIER

This study describes unidirectional influx of amino acids and D-glucos e across the small intestinal brush-border membrane of fully weaned ei ght week old pigs. Influx is minimal in the duodenum and maximal in th e distal and/or mid small intestine. Influx of beta-alanine, taurine a nd N-methyl-aminoisobutyric acid is chloride-dependent. The activation stoichiometry for taurine influx is 1.0 +/- 0.2 chloride/2.4 +/- 0.3 sodium/1 taurine. Influx of D-glucose, lysine, glycine and glutamate i s chloride-independent. An ABC test demonstrates a common beta-amino a cid carrier: (a) the apparent affinity constant K-1/2(Taurine) is 44 /- 13 mu M (means +/- S.D.) and the inhibitory constant (K-Taurine) ag ainst beta-alanine influx is 41 +/- 5 mu M (means +/- S.E.). (b) K-1/2 (beta-alanine) is 97 +/- 23 mu M and K-i(beta-alanine) against taurine influx is 160 +/- 22 mu M. (c) K-i(Hypotaurine) against taurine and b eta-alanine influx is 43 +/- 4 (n = 7) and 22 +/- 5 mu M (n = 7), resp ectively. In conclusion, a high affinity, low capacity, sodium- and ch loride-dependent carrier of beta-amino acids is present in pig small i ntestine.