Oleic acid uptake by jejunal and ileal rat brush border membrane vesicles

In previous works, a membrane fatty acid transport system has been identified in brush border membrane vesicles, but no different intestinal regions were considered in these studies. To test the existence of a proximal-to-distal gradient of fat absorption along the small intestine, transmembrane influx kinetics of a representative long-chain fatty acid, 3H-oleic acid, in both jejunum and ileum of rat has been studied using brush border membrane vesicles (BBMV). With increasing concentration of unbound oleate in the medium, both jejunal and ileal BBMV showed saturable uptake kinetics (Vmax = 0.15 +/- 0.01 nmol.mg protein-1 x 5 min-1 and Km = 136 +/- 29.1 nmol for jejunum, and Vmax = 0.23 +/- 0.03 nmol.mg protein-1 x 5 min1 and Km = 196 +/- 50.3 nmol for ileum). These results support the hypothesis that oleic acid uptake occurs via a carrier-mediated transport mechanism in both jejunum and ileum. Furthermore, the existence of a proximal-to-distal gradient for fat absorption was apparent with a higher density of transport units (Vmax) in ileum compared to jejunum.