CHLORIDE TRANSPORT IN BRUSH-BORDER MEMBRANE-VESICLES FROM CHICK JEJUNUM

This study sought to characterize the mechanism(s) of Cl- transport across brush-border membrane vesicles (BBMV) isolated from chick jejunum. An inwardly directed proton gradient stimulated chloride (Cl-36(-)) uptake. This uptake was inhibited by SITS and H-2-DIDS. pH-gradient-stimulated Cl- uptake was electroneutral, since it was only slightly decreased by voltage clamping the BBMV with K+ and valinomycin. An outwardly directed HCO3- gradient significantly increased chloride uptake in the presence of a pH gradient. pH-driven chloride uptake was reduced by the presence of several anions in the uptake buffer. The rank order of potency for inhibition of pH-driven Cl- uptake was Cl- > SCN- > HCO3- > I- > Glu(-) > HPO42-. In the absence of a pH gradient, chloride was less concentrated inside the vesicles than outside. Chloride uptake under these conditions was stimulated by a positive electrical potential inside the vesicles. This stimulation was inhibited by the addition of several anions outside the vesicles. The order of inhibitory potency was SCN- > I- > Cl- > HCO3- > Glu(-) > HPO42-. The results are consistent with the presence of a Cl-/base exchanger and a chloride conductance pathway in the brush-border membrane of chick small intestine.