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 co mpared with only an inward Na+ gradient, only an outward H+ gradient, or the absence of either Na+ or H+ gradients. The addition of mucin fu rther increased the enhanced uptake of oleic acid observed in the pres ence of opposing Na+/H+ gradients. Amiloride, an inhibitor of the Na+/ H+ exchanger, reduced by about 40% the uptake of oleic acid into sheet s of rat jejunum, and this inhibitory effect was observed over a range of rates of stirring of the bulk phase. In rabbit jejunal brush borde r membrane vesicles, amiloride reduced oleic acid uptake in the presen ce but not in the absence of opposing Na+/H+ gradients, with a K-i of approx. 36 mu M. Thus, oleic acid uptake occurs largely by partitionin g of the lipid into the brush border membrane, influenced by a process which involves the activation of the brush border membrane Na+/H+ exc hanger.