Linoleic acid uptake by isolated enterocytes: influence of alpha-linolenic acid on absorption

In a previous study we showed that intestinal uptake of alpha-linolenic acid (18:3n-3) was carrier-mediated and we suggested that a plasma membrane fatty acid protein was involved in the transport of long-chain fatty acids. To further test this hypothesis, the mechanism of linoleic acid (18:2n-6) uptake by isolated intestinal cells was examined using a rapid filtration method and 20 mM sodium taurocholate as solubilizing agent. Under these experimental conditions transport of [1-14C]linoleic acid monomers in the concentration range of 2 to 2220 nM was saturable with a Vm of 5.1 +/- 0.6 nmol/mg protein/min and a Km of 183 +/- 7 nM. Experiments carried out in the presence of metabolic inhibitors, such as 2,4-dinitrophenol and antimycin A, suggested that an active, carrier-mediated mechanism was involved in the intestinal uptake of this essential fatty acid. The addition of excess unlabeled linoleic acid to the incubation medium led to a 89% decrease in the uptake of [1-14C]linoleic acid, while D-glucose did not compete for transport into the cell. Other long-chain polyunsaturated fatty acids added to the incubation mixture inhibited linoleic acid uptake by more than 80%. The presence of alpha-linolenic acid (18:3n-3) in the incubation medium caused the competitive inhibition (Ki = 353 nM) of linoleic acid uptake. The data are compatible with the hypothesis that intestinal uptake of both linoleic, and alpha-linolenic acid is mediated by a membrane carrier common to long-chain fatty acids.