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J. Biochem, 1988, Vol. 104, No. 1 155-158
© 1988 Japanese Biochemical Society

research-article

Taurine Transport across Hepatocyte Plasma Membranes: Analysis in Isolated Rat Liver Sinusoidal Plasma Membrane Vesicles1

Masayasu Inoue*,2 and Irwin M. Arias**

*Department of Biochemistry, Kumamoto University Medical School 2-2-1 Honjo, Kumamoto 860
**Department of Physiology, Tufts University Medical School 136 Harrison Avenue, Boston, MA 02111, U.S.A.

2 To whom correspondence should be addressed

To elucidate the mechanism of taurine transport across the hepatic plasma membranes, rat liver sinusoidal plasma membrane vesicles were isolated and the transport process was analyzed. In the presence of a sodium gradient across the membranes (vesicle inside < vesicle outside), an overshooting uptake of taurine occurred. In the presence of other ion gradients (K+ Li+, and choline+), taurine uptake was very small and no such overshoot was observed. Sodium-dependent uptake of taurine occurred into an osmotically active intravesicular space. Taurine uptake was stimulated by preloading vesicles with unlabeled taurine (transstimulation) in the presence of NaCl, but not in the presence of KC1. Sodium-dependent transport followed saturation kinetics with respect to taurine concentration; double-reciprocal plots of uptake versus taurine concentration gave a straight line from which an apparent Km value of 0.38 mM and Vmax of 0.27 nmol/20 s x mg of protein were obtained. Valinomycin-induced K+-diffusion potential failed to enhance the rate of taurine uptake, suggesting that taurine transport does not depend on membrane potential. Taurine transport was inhibited by structurally related {omega}-amino acids, such as ß-alanine and {varepsilon}-aminobutyric acid, but not by glycine, {varepsilon}-aminocaproic acid, or other {alpha}-amino acids, such as L-alanine. These results suggest that Na+-dependent uptake of taurine might occur across the hepatic sinusoidal plasma membranes via a transport system that is specific for {omega}-amino acids having 2–3 carbon chain length.

1 This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture of Japan and by NIH grants AM-2019 and AM-35652.


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