CELLULAR-DIFFERENTIATION AND I-FABP PROTEIN EXPRESSION MODULATE FATTY-ACID UPTAKE AND DIFFUSION

The effect of cellular differentiation on fatty acid uptake and intrac ellular diffusion was examined in transfected pluripotent mouse embryo nic stem (ES) cells stably expressing intestinal fatty acid binding pr otein (I-FABP). Control ES cells, whether differentiated or undifferen tiated, did not express I-FABP. The initial rate and maximal uptake of the fluorescent fatty acid, itrobenz-2-oxa-1,3-diazol-4-yl)amino]-oct adecanoic acid (NBD-stearic acid), was measured in single cells by kin etic digital fluorescence imaging. I-FABP expression in undifferentiat ed ES cells increased the initial rate and maximal uptake of NBD-stear ic acid 1.7- and 1.6-fold, respectively, as well as increased its effe ctive intracellular diffusion constant (D-eff) 1.8-fold as measured by the fluorescence recovery after photobleaching technique. In contrast , ES cell differentiation decreased I-FABP expression up to 3-fold and decreased the NBD-stearic acid initial rate of uptake, maximal uptake , and D-eff by 10-, 4.7-, and 2-fold, respectively. There were no sign ificant differences in these parameters between the differentiated con trol and differentiated I-FABP-expressing ES cell lines. In summary, d ifferentiation and expression of I-FABP oppositely modulated NBD-stear ic acid uptake parameters and intracellular diffusion in ES cells.