title: Extracellular calcium is required for the polychlorinated biphenyl-induced increase of intracellular free calcium levels in cerebellar granule cell culture.
abstract: Recent studies from the laboratory indicate that polychlorinated biphenyl (PCB) congeners can alter signal transduction and calcium homeostasis in neuronal preparations. These effects were more pronounced for the ortho-substituted, non-coplanar congeners, although the mechanisms underlying these effects are not clear. In the present study the time-course and concentration-dependent effects of coplanar and non-coplanar PCBs on intracellular free calcium concentration ([Ca2+]i) in cerebellar granule cell cultures were compared using the fluorescent probe fura-2. The ortho-substituted congeners 2,2'-dichlorobiphenyl (DCB) and 2,2',4,6,6'-pentachlorobiphenyl (PeCB) caused a gradual increase of [Ca2+]i while the non-ortho-substituted congeners 4,4'-DCB and 3,3',4,4',5-PeCB had no effect. The increase of [Ca2+]i produced by 2,2'-DCB was time- and concentration-dependent. Further studies examined possible mechanisms for this rise in [Ca2+]i. In contrast to the muscarinic agonist carbachol, the effects of 2,2'-DCB on [Ca2+]i were not blocked by thapsigargin and required the presence of extracellular calcium. The effects of ortho-substituted PCBs may depend on their ability to inhibit calcium sequestration as 2,2'-DCB significantly inhibited 45Ca2+-uptake by microsomes and mitochondria while 3,3',4,4',5-PeCB had no effect. In addition, 2,2'-DCB significantly increased the binding of [3H]inositol 1,4,5-trisphosphate to receptors on cerebellar microsomes, suggesting another possible mechanism by which ortho-substituted PCBs can mobilize [Ca2+]i. These results show that PCBs increase [Ca2+]i in vitro via a mechanism that requires extracelluar calcium, and support previous structure-activity studies indicating that ortho-substituted PCBs are more potent than non-ortho-substituted PCBs.
authors.affiliation: Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA. mundy.william@epamail.epa.gov.
authors.forename: W R
authors.initials: WR
authors.lastname: Mundy
authors.forename: T J
authors.initials: TJ
authors.lastname: Shafer
authors.forename: H A
authors.initials: HA
authors.lastname: Tilson
authors.forename: P R
authors.initials: PR
authors.lastname: Kodavanti
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000633:toxicity*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D018721:Muscarinic Agonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D011078:Polychlorinated Biphenyls / Q000633:toxicity*; D051381:Rats; D020318:Rats, Long-Evans; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D013329:Structure-Activity Relationship; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D004785:Environmental Pollutants; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018721:Muscarinic Agonists; D018160:Receptors, Cytoplasmic and Nuclear; D019284:Thapsigargin; D002217:Carbachol; D011078:Polychlorinated Biphenyls; D007770:L-Lactate Dehydrogenase; D002118:Calcium