The very low density, low density and high density lipoproteins (VLDL, LDL, HDL), centrifugally separated from human plasma treated with 2,4,5,2',4',5'-hexachloro[14C]biphenyl (14C-HCB) contained approximately 50% of the 14C-HCB. 2. Normal skin fibroblasts were incubated at 4 degrees C for 37 degrees C for varying times with medium containing 10% serum, LDL or HDL labelled with 14C-HCB. Cellular incorporation of 14C-HCB from serum was temperature-dependent and occurred mainly during the first 30 minutes. Cellular accumulation of 14C-HCB from isolated lipoproteins was also rapid and was more efficient from HDL than from LDL or serum. Accumulation from HDL was concentration-dependent and temperature-dependent. 3. The efflux of 14C-HCB from cells into serum- or lipoprotein-containing medium occurred very rapidly and was most effective in the presence of 20% serum. The order of efficiency in removal of HCB from cells was 20% serum, 50 micrograms LDL protein/ml, and 120 micrograms HDL protein/ml. Little or no efflux from cells occurred into serum-free, lipoprotein-free medium. 4. HDL may be involved in the delivery of HCB to cells, a role in contrast to the generally accepted theory that HDL transports lipids from cells.
