Hypotaurine transport in brain slices: comparison with taurine and GABA

Hypotaurine uptake was compared to taurine and GABA uptakes in brain slices under identical experimental conditions. The slices effectively concentrated both hypotaurine and GABA from the medium, whereas taurine was taken up more slowly. The uptakes of these three structurally related amino acids were all saturable, consisting of one low- and one high-affinity transport component. The kinetic parameters of hypotaurine uptake were of the same order of magnitude as those of GABA uptake. All uptake systems were sensitive to temperature, metabolic poisons, and sodium omission. Hypotaurine uptake was inhibited by GABA, L-2,4-diaminobutyric acid (L-DABA), cysteic acid, and beta-alanine, but not by taurine. Taurine uptake was strongly reduced by hypotaurine, beta-alanine, and L-DABA, as well as by GABA, whereas GABA uptake was affected only by cystamine, L-DABA, and nipecotic acid. The uptake processes of hypotaurine, taurine, and GABA were thus fairly similar and showed properties characteristic for neurotransmitter uptake. Hypotaurine uptake resembled more GABA than taurine uptake. The present inhibition studies suggest that there may exist only one common two-component transport system for these three amino acids.