Enhanced uptake of taurine by basolateral plasma membrane vesicles isolated from developing rat liver

Inasmuch as taurine biosynthesis is decreased during early postnatal life, an efficient mechanism for taurine uptake by the liver must be present to maintain intracellular stores of this β-amino acid. Therefore, basolateral liver plasma vesicles prepared from 14-day and adult rats were used to examine taurine transport during development. For both age groups, the presence of an inwardly directed Na⁺ gradient stimulated the initial rate of taurine uptake and caused a transient accumulation of taurine above equilibrium. For all time points before equilibrium, taurine uptake was significantly greater with membrane vesicles from 14-day compared to adult rat livers. In contrast, no age-related differences in Na⁺-independent uptake as measured with a K* gradient were detected. With equal intravesicular and extravesicular Na⁺ concentrations, taurine uptake remained significantly greater in the younger age group. For both age groups, Na⁺-depend-ent taurine uptake was saturable but the apparent Km and Vmax for Na⁺-dependent taurine uptake were significantly greater in membrane vesicles from 14-day compared to adult rats. These findings suggest that an increased number of functional carriers for taurine are present in developing compared to adult basolateral plasma membrane perhaps reflecting the needs of the immature liver for this essential nutrient.