PH-DEPENDENT FLUORIDE TRANSPORT IN INTESTINAL BRUSH-BORDER MEMBRANE-VESICLES

Fluoride (F) absorption from the rat stomach and urinary bladder, hams ter cheek pouch, and the renal tubules of several species are pH gradi ent-dependent. These observations led to the hypothesis that F crosses these epithelia in the form of the undissociated acid, HF. Several re cent reports, however, have provided evidence that F absorption from t he rat small intestine is insensitive to the lumenal pH, We report her e our evidence that F uptake by rabbit intestinal brush border membran e vesicles (BBMV) occurred rapidly and with an overshoot only in the p resence of an inward-directed proton gradient. In the absence of a pro ton gradient or in the presence of an outward-directed gradient, F upt ake was slow and without an overshoot. In the presence of an inward-di rected proton gradient, F uptake was partially inhibited by DIDS and D EP but not by diBAC. PCMBS inhibited F uptake by up to 83% in a dose-r esponse manner. DiBAC appeared to reduce intravesicular pH slightly bu t the other reagents had no effect. When the uptake buffer contained c hloride or nitrate, F uptake was partially inhibited compared to the m annitol or gluconate controls. It was concluded that F transport acros s the rabbit intestinal BBMV occurs via a carrier-mediated process whi ch may involve cotransport of F with H+ or exchange of F with OH-. The inhibitory effects of DIDS, DEP and PCMBS may occur by affecting this carrier-mediated transport. (C) 1998 Elsevier Science B.V. All rights reserved.