Active transport of fluoride by the rat intestine in vitro

• 1.

  1. Everted sacs of rat jejunum, ileum, and colon were used to investigate the possibility of active F⁻ transport. Fluoride was placed in equal concentration in both compartments at the initial levels of 0.083, 0.167, and 1.670 mM. A secretion of F⁻ against its electrochemical gradient was observed across ileum at 0.167 mM F⁻ and either 1.9 or 1.0 mM Ca²⁺, and across jejunum and ileum at 0.167 and 1.670 mM F⁻ in the presence of 0.5 mM Ca²⁺.

• 2.

  2. When 0.167 mM F⁻ was placed initially on either the mucosal or the serosal| side, at 1.9 mM Ca²⁺, fluoride crossed each section of the intestine freely in both the absorptive and secretory directions. The translocation of F⁻, however, was greater in the direction of secretion with jejunal and ileal sacs.

• 3.

  3. With equal initial concentration of F⁻ in both compartments, alteration of| the exogenous Ca²⁺ concentration and also the addition of 2,4-dinitrophenol affected only the net movement of F⁻ in the mucosal compartment. Since the loss of F⁻ from the serosal compartment was not influenced, it appeared that this effect was localized at the mucosal surface.

• 4.

  4. The net movement of F⁻ against its electrochemical gradient was inhibited| by the addition of 1 mM dinitrophenol at 0° confirming the existence of active F⁻ transport in jejunum and ileum. A less active F⁻ pump also appeared to exist in the colon.