Taurine transport by rat intestine.

Rat intestinal transport of taurine was studied using jejunal brushborder membrane vesicles and everted jejunal sacs. Membrane vesicle experiments showed that the initial rate (at 10 s) of 10 microM taurine uptake was stimulated 3.5-fold by an inwardly directed Na+ gradient when compared with a K+ gradient. The Cl- salt of Na+ supported uptake to a significantly greater degree than did more (SCN-) or less (SO2-4) permeant salts. Na+-stimulated uptake at 1 min achieved a value 2.5 times greater than equilibrium ("overshoot"). When 10 s taurine uptake was determined over a range of taurine concentrations (10-1,000 microM) and plotted using the Woolf-Hofstee equation, a diffusive and carrier-mediated component was apparent. Half-maximal, carrier-mediated uptake occurred at 25 +/- 9 microM taurine (Km). An inside-negative, valinomycin-induced K+ diffusion potential stimulated 10-s taurine uptake when compared with voltage-clamped conditions (4.9 vs. 2.6 pmol/mg protein; P less than 0.05). Incubation with a structural analogue, hypotaurine, reduced 10-s taurine uptake by 89%. Uptake by everted jejunal sacs also demonstrated Na+ stimulation and inhibition by hypotaurine. These data confirm the existence of a high-affinity rat jejunal brush-border membrane-associated taurine transport mechanism that is electrogenic, stimulated by a Na+ gradient, and modified by external Cl-.