Ontogenesis of intestinal taurine transport: evidence for a beta-carrier in developing rat jejunum

Taurine, a sulfur-containing beta-amino acid, may be conditionally essential during development. However, the existence of a carrier system for beta-amino acids has not been demonstrated in brush-border membrane vesicles (BBMV) from adult rat jejunum. We studied the uptake of [3H]taurine in BBMV prepared from the jejunum of developing and adult rats using a cation-precipitation technique. Uptake of 10 microM [3H]taurine by adult BBMV was slightly enhanced in the presence of an inwardly directed 100 mM Na+ gradient compared with a K+ gradient, and there was no intravesicular accumulation of isotope above the equilibrium concentration ("overshoot"). In contrast, taurine transport by BBMV from 10-day-old rat pups was markedly accelerated in the presence of a Na+ gradient compared with a K+ gradient and a twofold overshoot was observed. Na+-dependent taurine uptake was inhibited by the structural analogues hypotaurine and beta-alanine but not by alpha-alanine or glutamine, which are amino acids served by other transport systems. By computer analysis, Na+-dependent taurine uptake (2-1,000 microM) was saturable with an apparent Km of 74.80 +/- 11.87 microM and a Vmax of 53.55 +/- 2.76 pmol.mg protein-1.min-1. With increasing postnatal age, there was a marked decrease in the initial rate and peak intravesicular accumulation of taurine with disappearance of the overshoot by 21 days of age. We conclude 1) a Na+-dependent carrier mechanism for taurine transport is present in the brush-border membrane of suckling rat jejunum and 2) the activity of this carrier decreases after weaning.(ABSTRACT TRUNCATED AT 250 WORDS)