Functional characterization of sodium- and chloride-dependent taurine transport in human keratinocytes

Abstract

In the skin, taurine acts as an important osmolyte required for keratinocyte hydration. It has antioxidant effects, protects cells from UV-induced stress and has effects on cell proliferation, inflammation and collagenogenesis. This study was performed to find and characterize functionally a taurine transport system in keratinocytes and to establish a cell culture model for skin taurine transport studies. Uptake of [ 3H]taurine was studied both in the human adult low calcium high temperature (HaCaT) cell line and in human native epidermal keratinocytes. Uptake of [ 3H]taurine in HaCaT cells was strictly dependent on extracellular sodium and chloride. The taurine uptake rate was saturable and indicated participation of a single transport system with kinetic parameters of K t =5.1±0.2 μM and V max=320.5±2.8 pmol/10 min per mg of protein. Uptake was strongly inhibited by β-amino acids (taurine, β-alanine, hypotaurine, β-guanidinopropionic acid), whereas α- and γ-amino acids had little or no effect. Taurine uptake in normal keratinocytes was very similar to that in HaCaT cells with respect to substrate specificity and affinity. We conclude that keratinocytes express the Na + and Cl − dependent, high-affinity taurine transporter. This system accepts β- and certain γ-amino acids as substrates.