Active transport of taurine in rabbit jejunal brush-border membrane vesicles

Abstract

The characteristics of taurine uptake in rabbit jejunal brush-border membrane vesicles were investigated. Taurine was transiently accumulated inside the vesicles against a concentration gradient when an inwardly directed NaCl gradient was imposed across the membrane. Uptake of taurine showed an absolute requirement for both Na+ and Cl-. The NaCl gradient-dependent taurine uptake was stimulated by a valinomycin-induced, inside-negative, K+-diffusion potential, suggesting that the uptake process was electrogenic. The uptake system exclusively interacted with beta-amino acids of small size, but had no affinity for alpha-amino acids. Kinetic analysis revealed that the system exhibited high affinity for taurine (Kt = 14.4 +/- 0.5 microM). Taurine uptake was greatly influenced by extravesicular concentrations of Na+ and Cl-. The Cl- stoichiometry was found to be one. In the presence of Cl-, taurine uptake was sigmoidally related to Na+ concentration, and the Na+ stoichiometry was calculated to be three. Thus three Na+ and one Cl- were involved per transport of one taurine molecule. The uptake process was not affected by other transport inhibitors such as amiloride, harmaline, furosemide, and 4,4'-diisothiocyanostilbene-2,2'-disulfonate.