Taurine transport by rat intestine

Rat intestinal transport of taurine was studied using jejunal brush-border membrane vesicles and everted jejunal sacs. Membrane vesicle experiments showed that the initial rate (at 10 s) of 10 μM 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 (SO₄^2-) 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 μM) and plotted using the Woolf-Hofstee equation, a diffusive and carrier-mediated component was apparent. Half-maximal, carrier-mediated uptake occurred at 25 ± 9 μM taurine (K(m)). 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 < 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^-.