Journal Article

Calcium-Related Processes Involved in the Inhibition of Depolarization-Evoked Calcium Increase by Hydroxylated PBDEs in PC12 Cells

Milou M. L. Dingemans, Martin van den Berg, Åke Bergman and Remco H. S. Westerink

in Toxicological Sciences

Volume 114, issue 2, pages 302-309
Published in print April 2010 | ISSN: 1096-6080
Published online December 2009 | e-ISSN: 1096-0929 | DOI: http://dx.doi.org/10.1093/toxsci/kfp310
Calcium-Related Processes Involved in the Inhibition of Depolarization-Evoked Calcium Increase by Hydroxylated PBDEs in PC12 Cells

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In vitro studies indicated that hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have an increased toxic potential compared to their parent congeners. An example is the OH-PBDE–induced increase of basal intracellular Ca2+ concentration ([Ca2+]i) by release of Ca2+ from endoplasmic reticulum (ER) and mitochondria and/or influx of extracellular Ca2+. ER and mitochondria regulate Ca2+ homeostasis in close association with voltage-gated Ca2+ channels (VGCCs). Therefore, effects of (OH-)PBDEs on the depolarization-evoked (100mM K+) net increase in [Ca2+]i (depolarization-evoked [Ca2+]i) were measured in neuroendocrine pheochromocytoma cells using the Ca2+-responsive dye Fura-2. OH-PBDEs dose dependently inhibited depolarization-evoked [Ca2+]i. This inhibition was potentiated by a preceding increase in basal [Ca2+]i. Especially at higher concentrations of OH-PBDEs (5–20μM), large increases in basal [Ca2+]i strongly inhibited depolarization-evoked [Ca2+]i. The inhibition appeared more sensitive to increases in basal [Ca2+]i by Ca2+ release from intracellular stores (by 3-OH-BDE-47 or 6′-OH-BDE-49) compared to those by influx of extracellular Ca2+ (by 6-OH-BDE-47 or 5-OH-BDE-47). The expected [Ca2+]i difference close to the membrane suggests involvement of Ca2+-dependent regulatory processes close to VGCCs. When coapplied with depolarization, some OH-PBDEs induced also moderate direct inhibition of depolarization-evoked [Ca2+]i. Polybrominated diphenyl ethers and methoxylated BDE-47 affected neither basal nor depolarization-evoked [Ca2+]i, except for BDE-47, which moderately increased fluctuations in basal [Ca2+]i and depolarization-evoked [Ca2+]i. These findings demonstrate that OH-PBDEs inhibit depolarization-evoked [Ca2+]i depending on preceding basal [Ca2+]i. Related environmental pollutants that affect Ca2+ homeostasis (e.g., polychlorinated biphenyls) may thus also inhibit depolarization-evoked [Ca2+]i, justifying further investigation of possible mixture effects of environmental pollutants on Ca2+ homeostasis.

Keywords: brominated flame retardant; calcium homeostasis; calcium signaling; calcium-induced VGCC inhibition; depolarization-evoked calcium influx; in vitro neurotoxicity

Journal Article.  4222 words.  Illustrated.

Subjects: Medical Toxicology ; Toxicology (Non-medical)

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