ToxSci Advance Access originally published online on December 4, 2008
Toxicological Sciences 2009 107(2):490-497; doi:10.1093/toxsci/kfn249
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Hexabromocyclododecane Inhibits Depolarization-Induced Increase in Intracellular Calcium Levels and Neurotransmitter Release in PC12 Cells
* Institute for Risk Assessment Sciences (IRAS), Utrecht University, NL-3508 TD Utrecht, The Netherlands
Department of Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden
1 To whom correspondence should be addressed at Institute for Risk Assessment Sciences, (IRAS), Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands. Fax: +31-30-253-5077. E-mail: m.dingemans{at}uu.nl.
Received September 12, 2008; accepted November 20, 2008
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Abstract |
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Environmental levels of the brominated flame retardant (BFR) hexabromocyclododecane (HBCD) have been increasing. HBCD has been shown to cause adverse effects on learning and behavior in mice, as well as on dopamine uptake in rat synaptosomes and synaptic vesicles. For other BFRs, alterations in the intracellular Ca2+ homeostasis have been observed. Therefore, the aim of this study was to investigate whether the technical HBCD mixture and individual stereoisomers affect the intracellular Ca2+ concentration ([Ca2+]i) in a neuroendocrine in vitro model (PC12 cells). [Ca2+]i and vesicular catecholamine release were measured using respectively single-cell Fura-2 imaging and amperometry. Exposure of PC12 cells to the technical HBCD mixture or individual stereoisomers did neither affect basal [Ca2+]i, nor the frequency of basal neurotransmitter release. However, exposure to HBCD (0-20µM) did cause a dose-dependent reduction of a subsequent depolarization-evoked increase in [Ca2+]i. This effect was apparent only when HBCD was applied at least 5 min before depolarization (maximum effect after 20 min exposure). The effects of 
- and β-HBCD were comparable to that of the technical mixture, whereas the inhibitory effect of 
-HBCD was larger. Using specific blockers of L-, N- or P/Q-type voltage-gated Ca2+ channels (VGCCs) it was shown that the inhibitory effect of HBCD is not VGCC-specific. Additionally, the number of cells showing depolarization-evoked neurotransmitter release was markedly reduced following HBCD exposure. Summarizing, HBCD inhibits depolarization-evoked [Ca2+]i and neurotransmitter release. As increasing HBCD levels should be anticipated, these findings justify additional efforts to establish an adequate exposure, hazard and risk assessment.
Key Words: brominated flame retardants; exocytosis; in vitro; ion channels; neurotoxicity; voltage-gated calcium channels.
2 These authors have contributed equally.