L-FABP and I-FABP expression increase NBD-stearate uptake and cytoplasmic diffusion in L cells.

The effects of intestinal and liver fatty acid binding protein (I- and L-FABP, respectively) expression on single-cell fatty acid uptake, internalization, and cytoplasmic diffusion were determined in transfected L cell fibroblasts. These parameters were measured using the nonesterifiable fluorescent fatty acid probe 12- N-methyl-(7-nitrobenz-2-oxa-1,3-diazol)aminostearate (NBD-stearate) and fluorescence digital imaging. In single-cell fluorescence imaging experiments, L-FABP-expressing cells, but not I-FABP-expressing cells, increased NBD-stearate uptake 1.7-fold compared with control cells. Both I- and L-FABP increased the cytoplasmic diffusion rate of the internalized NBD-stearate 2.6- and 1.9-fold, respectively, compared with control cells. However, increased NBD-stearate lateral membrane mobility was observed only in L-FABP-expressing cells. After incubation of the cells with 4 μM NBD-stearate at 37°C for 30 min, fluorescence deconvolution imaging indicated that NBD-stearate was localized primarily into lipid droplets in all cell lines. The differential effect of these proteins on fatty acid uptake and intracellular trafficking in single cells illustrates a possible difference in the physiological function of I- and L-FABP in intact cells.