Molecular characterization of taurine transport in bovine aortic endothelial cells

Abstract

Cultured bovine aortic endothelial (BAE) cells expressed a Na+/Cl−-dependent taurine uptake activity that saturated with an apparent K0.5 of ∼4.9 μM for taurine and was inhibited by β-alanine, guanidinoethane sulfonate, and homotaurine. We isolated a taurine transporter clone from a BAE cell cDNA library that revealed >91% sequence identity at the amino acid level to the previously cloned high-affinity mammalian taurine transporters. The biochemical and pharmacological properties of the bovine taurine transporter cDNA expressed in Xenopus oocyte was similar to those of the high-affinity taurine transporter. Surprisingly, F− blocked taurine uptake in BAE cells with an IC50 of ∼17.5 mM. The endogenous taurine uptake was also inhibited by the protein kinase C activator phorbol 12-myristate 13-acetate, but not by its inactive analog, 4α-phorbol 12,13-didecanoate. The endogenous uptake was stimulated, however, by hypertonic stress and the increase was due to an increase in the Vmax of taurine uptake. Our results provide the first description of a molecular mechanism that may be responsible for maintaining the intracellular taurine content in the endothelial cells.