Taurine and β-alanine transport in an established human kidney cell line derived from the proximal tubule

Abstract

The transport mechanisms of taurine and β-alanine by an immortalized human embryonic kidney epithelial cell line (IHKE) were examined. The uptake of these β-amino acids was characterized by two Na +-dependent transport components, whereas an inwardly directed H +-gradient only stimulated amino acid influx to a small extent and in the absence of sodium. Competition experiments revealed that taurine and β-alanine drastically reduced the uptake of one another by the high-affinity Na +-dependent transport system. However, some α-amino acids could also compete with the β-amino acids, but with a low affinity. Examinations of the effect of different anions on the Na +-dependent uptake of taurine at a low amino acid concentration (240 nM) revealed a specific requirement for Cl −, whereas Cl − had no measurable effect at a higher concentration (1.0 mM) of taurine. In addition, activation of taurine transport as a function of Na + and Cl − concentration indicated a probable coupling ratio of 3 Na +/1 Cl −/1 taurine for the high-affinity carrier. Finally, cellular regulation of taurine transport was indicated by the finding that pretreatment with taurine containing media decreased the activity of the taurine transporter(s).