LOCALIZATION AND REGULATION OF THE PUTATIVE MEMBRANE FATTY-ACID TRANSPORTER (FAT) IN THE SMALL-INTESTINE - COMPARISON WITH FATTY-ACID-BINDING PROTEINS (FABP)

The expression of the putative membrane fatty-acid transporter (FAT) w as investigated in the small intestine. The FAT mRNA level was higher in the jejunum than in the duodenum and was lower in the ileum, as obs erved for cytosolic fatty-acid-binding proteins (FABP) expressed in th is tissue. No FAT transcript was found in the stomach or colon. FAT mR NA was constitutively expressed in the epithelial cells located in the upper two thirds of villi, while it was undectectable in the crypt ce lls and submucosal cells. In jejunal mucosa, immunochemical studies sh owed that FAT protein was limited to the brush border of enterocytes. No fluorescence was found in the goblet cells. To determine whether FA T responded to changes in fat intake, as reported for FABP, the effect of two high-fat diets, which essentially contained either medium-chai n fatty acids or long-chain fatty acids (sunflower-oil dirt), was inve stigated. The sunflower-oil diet greatly increased FAT mRNA abundance throughout the small intestine. In contrast, a weak effect of medium-c hain fatty acids was observed only in the jejunum. As found for FABP e xpression, treatment with the hypolipidemic drug bezafibrate affected FAT expression. These data demonstrate that FAT and FABP are co-expres sed in enterocytes, as has been shown in adipocytes, myocytes and mamm ary cells. The data suggest that these membrane and cytosolic proteins might have complementary functions during dietary-fat absorption.