Uncoupling effect of mercuric chloride on mitochondria isolated from an hepatic cell line

A human fetal hepatic cell line (WRL-68) was used as a model to study the d amage produced by mercury. The Hg(II) uptake by WRL-68 cells was found to b e in a biphasic manner with a rapid initial uptake phase lasting about 5 mi n, followed by a sustained phase of slower accumulation. Distribution of me rcury was studied and mitochondria were found to be the major target for me rcury in this cell line (48%), followed by nuclei (38%), cytosol (8%) and m icrosomes (7%). Mitochondrial morphological damage after mercury treatment was observed by transmission electron microscopy. To determine if the toxic effect of mercury on mitochondrial bioenergetics was direct or indirect, m itochondria were isolated from WRL-68 cells after 1 h of pre-incubation wit h 0.5 muM HgCl2. Oxygen consumption was quantified in two sets of experimen ts: in the presence of classical mitochondrial respiratory inhibitors; and in the presence of oligomycin. No significant difference was found in respi ration with classical inhibitors, indicating that mercury does not affect d irectly the mitochondrial respiratory chain. However, mitochondria of Hg-tr eated cells were not inhibited when oligomycin was added, probably due to a n uncoupling effect. This effect was prevented with dithiothreitol (DTT) tr eatment. A possible explanation for mercury's effect on mitochondria and it s relation with oxidative stress is presented. Copyright (C) 2001 John Wile y & Sons, Ltd.