Intestinal fatty acid binding protein may favor differential apical fatty acid binding in the intestine

The intestinal mucosa metabolizes fatty acids differently when presented to the lumenal or basolateral membrane. Expression of both liver and intestin al fatty acid binding proteins (L- and I-FABPs) uniquely in the enterocyte offers a possible explanation of this phenomenon. An organ explant system w as used to analyze the relative binding of fatty acids to each protein. Mor e fatty acid was bound to L-FABP than to I-FABPs (28% vs. 6% of cytosolic r adioactivity), no matter on which side the fatty acid was added. However, a 2-3-fold increase in fatty acid binding to the intestinal paralog was note d after apical addition of palmitic or oleic acid in mucosa from chow fed r ats. When oleic acid was added apically, a 1.4-fold increase in binding to I-FABP was observed in mucosa derived from chronically fat fed rats, consis tent with the previously observed 50% increase in the content of that prote in. Immunocytochemical localization of both FABPs in vivo demonstrated an a pical cytoplasmic localization in the fasting state, and redistribution to the entire cytoplasm after fat feeding. These data are consistent with the hypothesis that I-FABP may contribute to the metabolic compartmentalization of apically presented fatty acids in the intestine. (C) 2000 Elsevier Scie nce B.V. All rights reserved.