Fatty acid uptake and metabolism in a human intestinal cell line (Caco-2): comparison of apical and basolateral incubation.
Free fatty acids can enter the enterocyte via the apical or basolateral plasma membrane. We have used the Caco-2 intestinal cell line to examine the polarity of free fatty acid uptake and metabolism in the enterocyte. Differentiated Caco-2 cells form polarized monolayers with tight junctions, and express the small intestine-specific enzymes sucrase and alkaline phosphatase. Cells were grown on permeable polycarbonate Transwell filters, thus allowing separate access to the apical and basolateral compartments. Total uptake of [3H]palmitate bound to bovine serum albumin (palmitate-BSA 4:1) was twofold higher (P less than 0.05 or less) at the apical surface than at the basolateral surface. The relative apical and basolateral membrane surface areas of the Caco-2 cells, as measured by partition of the fluorophore trimethylammonium-diphenylhexatriene TMA-DPH), was found to be 1:3. Thus, apical fatty acid uptake was sixfold higher than basolateral uptake per unit surface area. Analysis of metabolites after incubation with submicellar concentrations of [3H]palmitate showed that the triacylglycerol to phospholipid (TG:PL) ratio was higher for fatty acid added to the apical as compared to the basolateral compartment (20% at 60 min, P less than 0.025). Little fatty acid oxidation was observed. Preincubation with albumin-bound palmitate, alone or with monoolein, increased the incorporation of both apical and basolateral free fatty acids into TG. The results suggest that the net uptake of long-chain free fatty acids across the apical plasma membrane is greater than uptake across the basolateral membrane. In addition, a small increase in the TG:PL ratio for apically, compared to basolaterally, added free fatty acids suggests that polarity of metabolism occurs to a limited extent in Caco-2 enterocytes.
Trotter
P J
PJ
Department of Nutrition, Harvard School of Public Health, Harvard Medical School, Boston, MA 02115.
Storch
J
J
D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000378:metabolism*; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism* / Q000648:ultrastructure; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D005227:Fatty Acids; D010169:Palmitic Acids; D010743:Phospholipids; D014280:Triglycerides; D019308:Palmitic Acid