Effect of albumin, low temperature and metabolic inhibitors on transport of fatty acids into cultured human leukemic myeloid cells.
Radioactively-labelled palmitic acid was used to study the effects of albumin, low temperature and several inhibitors of metabolism on transport of fatty acids into cultured human leukemic myeloid cells. When serum or albumin were present in the medium, uptake of fatty acid by cells as well as its further incorporation into phospholipids and neutral lipids were considerably reduced. Uptake and metabolic utilization of this fatty acid was reduced at low temperature, in the presence or absence of albumin in the incubation medium. In absence of albumin, addition of iodoacetate, sodium cyanide or sodium azide had but little effect on the total uptake of fatty acids while metabolic utilization was reduced. When albumin was present, these inhibitors reduced both total uptake and incorporation into lipids. The data suggest that incorporation of the fatty acid into the outer layer of the cell membrane is controlled by the concentration of free, uncomplexed molecules of fatty acid adjacent to the cell surface. In the absence of albumin this is a fast reaction which reaches nearly maximal uptake in three minutes. In the presence of albumin, this process is much slower and follows a nearly linear course between 3 and 60 minutes. Translocation into the inner layer of the membrane and subsequent utilization for metabolic processes is a much slower process, which seems to depend on the quantity of the fatty acid in the outer layer.