Molecular characterization of taurine transport in bovine aortic endothelial cells

Cultured bovine aortic endothelial (BAE) cells expressed a Na+/Cl--dependen t taurine uptake activity that saturated with an apparent K-0.5 of similar to4.9 muM for taurine and was inhibited by beta -alanine, guanidinoethane s ulfonate, and homotaurine. We isolated a taurine transporter clone from a B AE cell cDNA library that revealed > 91% sequence identity at the amino aci d level to the previously cloned high-affinity mammalian taurine transporte rs. The biochemical and pharmacological properties of the bovine taurine tr ansporter cDNA expressed in Xenopus oocyte was similar to those of the high -affinity taurine transporter. Surprisingly, F- blocked taurine uptake in B AE cells with an IC50 of similar to 17.5 mM. The endogenous taurine uptake was also inhibited by the protein kinase C activator phorbol 12-myristate 1 3-acetate, but not by its inactive analog, 4 alpha -phorbol 12,13-didecanoa te. The endogenous uptake was stimulated, however, by hypertonic stress and the increase was due to an increase in the V-max of taurine uptake. Our re sults provide the first description of a molecular mechanism that may be re sponsible for maintaining the intracellular taurine content in the endothel ial cells. (C) 2000 Elsevier Science B.V. All rights reserved.