Distinction between chloride-dependent transport systems for taurine and beta-alanine in rabbit ileum.

This study describes the influx of taurine and beta-alanine across the brush-border membrane of rabbit distal ileum. The kinetics of JmcTau [concentration at which half-maximal activation occurs (K1/2) = 41 microM and Jmax = 24 nmol.cm-2.h-1] are consistent with the kinetics of taurine uptake by jejunal brush-border vesicles. The taurine carrier differs from the beta-alanine carrier by being insensitive to leucine inhibition and by the jejunoileal variation of influx along the small intestine. The K1/2 for sodium and chloride activation of the beta-alanine carrier (48 and 8 mM, respectively) differ markedly from the values reported for the taurine carrier. In addition, taurine is not transported by the beta-alanine carrier. Thus the study demonstrates that the taurine and beta-alanine carriers are separate entities, and it adds to the imino and the taurine carriers the beta-alanine carrier as a third chloride-dependent intestinal transporter of amino acids.