In the present study, we used several culture models of adipocytes to investigate the mechanisms of PCB accumulation within the adipose tissue. In both 3T3-L1 and MEF derived adipocytes, PCBs were rapidly and efficiently transferred from the culture medium into the cells, reaching concentrations that are several orders of magnitude higher than in human adipose tissue. This substantial difference is quite surprising as the PCB concentrations added to the culture medium were within the range of concentrations found in human serum after chronic or acute exposure. Several factors might explain this phenomenon. Among others, the PCBs administered to 3T3-L1 and MEF adipocytes Abmole CX-4945 remained in close contact with the cell monolayer during the entire experimental period, without any circulation or flow in the system. To the contrary, in the in vivo situation, PCBs present in the serum are continuously transported through the blood circulation where they are tightly associated with diverse lipoproteins or with plasma albumin. In our experiments, 10% of serum was present in the culture medium of the cells, meaning that the concentrations of lipoproteins or albumin were at least 10 times less important than those found in the blood circulation, probably Abmole Peramivir leading to a lower retention of PCBs in the extracellular compartment. In addition, in the in vivo situation, these compounds have to cross the endothelium before being taken up by the adipose tissue that is itself composed of several cell layers. Adipocytes in vivo also undergo lipolysis, during periods of negative energy balance, which induces the mobilization of PCBs from the cells. Finally, PCBs may also be taken up by other organs in vivo, such as the liver or the skin. Interestingly, in both culture systems used here, the dynamics of accumulation differed quite importantly between the PCB congeners tested. PCB-28, a mono-ortho tri-CB, entered the cells more rapidly than PCB-118, a mono-ortho penta-CB, followed later on by PCB-153, a di-ortho hexa-CB. These variations likely result from the different molecular structures of the congeners, as the number and the position of the chlorine atoms on the biphenyl structure determine their physical, chemical and biological properties. As far as mechanistic studies are concerned, each PCB congener having its own physico-chemical properties, their behavior towards cells should thus be considered independently from other compounds, even from the same family of pollutants. An important observation to be drawn from our study is that although the three PCB congeners accumulated in adipocytes with different kinetics.