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-glucose across the small intestinal brush-border membrane of fully weaned eight week old pigs. Influx is minimal in the duodenum and maximal in the distal and/or mid small intestine. Influx of β-alanine, taurine and N-ethyl-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 is chloride-independent. An ABC test demonstrates a common β-amino acid carrier: (a) the apparent affinity constant K _{1 2}^Taurine is 44 ± 13 μM (means ± S.D.) and the inhibitory constant (K_i^Taurine) against β-alanine influx is 41 ± 5 μM (means ± S.E.). (b) K _{1 2}^β-alanine is 97 ± 23 μM and K_i^β-alanine against taurine influx is 160 ± 22 μM. (c) K_i^Hypotaunne against taurine and β-alanine influx is 43 ± 4 (n = 7) and 22 ± 5 μM (n = 7), respectively. In conclusion, a high affinity, low capacity, sodium- and chloride-dependent carrier of β-amino acids is present in pig small intestine.