Oleic acid uptake into rat and rabbit jejunal brush border membrane.

Oleic acid uptake was studied using adult rabbit and rat jejunal brush border membrane vesicles. There was a reduction of oleic acid uptake following trypsin-treatment. Opposing Na+/H+ gradients (inward Na+ and outward H+ gradients) increased oleic acid uptake by about 40%, as compared with only an inward Na+ gradient, only an outward H+ gradient, or the absence of either Na+ or H+ gradients. The addition of mucin further increased the enhanced uptake of oleic acid observed in the presence of opposing Na+/H+ gradients. Amiloride, an inhibitor of the Na+/H+ exchanger, reduced by about 40% the uptake of oleic acid into sheets of rat jejunum, and this inhibitory effect was observed over a range of rates of stirring of the bulk phase. In rabbit jejunal brush border membrane vesicles, amiloride reduced oleic acid uptake in the presence but not in the absence of opposing Na+/H+ gradients, with a Ki of approx. 36 microM. Thus, oleic acid uptake occurs largely by partitioning of the lipid into the brush border membrane, influenced by a process which involves the activation of the brush border membrane Na+/H+ exchanger.