MECHANISM OF FLUORIDE ABSORPTION FROM THE RAT SMALL-INTESTINE

Fluoride (F) is readily absorbed from the small intestine. In many epithelia, F transport appears to occur predominantly as the weak acid HF. For the same mechanism to exist in intestinal epithelium, with the high pH of the intestinal lumen (and thus low proportion of HF), the discrimination in favor of HF vs F- would have to exceed 104:1. We have investigated the mechanism of intestinal F absorption in vitro, using segments of rat jejunum mounted in a modified Ussing apparatus. F was added to the mucosal buffer (0.1-1.0 mM F), and mucosal to serosal F transfer was measured after 30 minutes. F transfer was proportional to mucosal F concentration, but was found not to be pH dependent within the range pH 6.0-8.0. F transfer was strongly affected by changing the transmural potential difference (by substitution of Cl- and Na+, and by ouabain inhibition). The data indicate that intestinal F passage occurs predominantly as the anion F- rather than the weak acid HF. © 1990 Pergamon Press plc.