Taurine and hypotaurine transport by a single system in cultured neuroblastoma cells

The kinetics of mutual inhibition of taurine and hypotaurine uptake were studied using neuroblastoma C1300 cells as neuronal model. Hypotaurine and GABA inhibited taurine uptake competitively, increasing the apparent Km. High-affinity uptake of hypotaurine was completely abolished and the low-affinity component competitively inhibited by taurine. GABA affected noncompetitively low-affinity hypotaurine uptake, whereas the effect on high-affinity uptake was competitive, with an increase in the apparent Km. All structural analogues tested inhibited taurine and hypotaurine uptakes similarly. The most potent inhibitors were beta-alanine and 2-guanidinoethanesulphonic acid. The mutual inhibition and similar specificity profiles of taurine and hypotaurine uptakes showed that these amino acids employ a single transport system in neuroblastoma cells. Competitive inhibition by GABA of the high-affinity uptake of taurine and hypotaurine further suggests that also GABA uses the same carrier system.