ToxSci Advance Access originally published online on September 26, 2003
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Toxicological Sciences 76, 328-337 (2003)
Copyright © 2003 by the Society of Toxicology
IMMUNOTOXICOLOGY |
Ortho-Substituted PCBs Kill Thymocytes
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* University at Albany, School of Public Health, Department of Environmental Health and Toxicology, Rensselaer, New York 12144;
New York State Department of Health, Wadsworth Center, Albany, New York 12201; and
University at Albany, Institute for Health and the Environment and School of Public Health, Department of Environmental Health and Toxicology, Rensselaer, New York 12144
The effects of exposure of acutely dissociated rat thymocytes to various polychlorinated biphenyl (PCB) congeners were examined using flow cytometry. Non-planar, ortho-substituted congeners caused a rapid cell death at low micromolar concentrations, while coplanar, dioxin-like congeners at the same concentration were without significant effect. The most potent of the congeners studied was PCB 52 (2,2',5,5'-tetrachlorobiphenyl), which had an IC50 of 3.96 µM at 20 min. Prior to loss of viability there was a decrease in mitochondrial membrane potential 
m, an accumulation of intracellular calcium, and a progressive leakiness of the plasma membrane. Application of PCB 52 in calcium-free medium reduced the calcium accumulation, but did not reduce cell death. Agents that depolarized mitochondria also did not induce the same degree of cell death caused by PCB 52. Cyclosporin A, which prevents opening of the mitochondria permeability transition channel, protected against cell death but did not protect against mitochondrial depolarization or calcium accumulation. Rapamycin and FK 506 at high concentration provided partial protection against cell death. These observations indicate that the ortho-substituted PCB 52 disrupts plasma, mitochondrial and endoplasmic reticulum membranes. We hypothesize that PCB 52 incorporates into lipid bilayers and with its bulky, three-dimensional ortho-substituted congener structure disrupts membrane function to a greater degree than coplanar congeners.
Key Words: rat; mitochondria; endoplasmic reticulum; calcium; membrane potential; coplanar PCBs; cyclosporin A; lipid bilayers; mitochondrial permeability transition channel.
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