title: Acute exposure to methylmercury causes Ca2+ dysregulation and neuronal death in rat cerebellar granule cells through an M3 muscarinic receptor-linked pathway.
abstract: Acute exposure to low concentrations of methylmercury (MeHg) causes a severe loss of intracellular calcium (Ca2+(i)) homeostasis, which apparently contributes to neuronal death of cerebellar granule cells in culture. We examined the role of muscarinic receptors in MeHg-induced Ca2+ dysregulation and cell death in rat cerebellar granule cells in vitro using fura-2 single-cell microfluorimetry and viability assays, respectively. The nonspecific muscarinic receptor antagonist atropine significantly delayed the onset of MeHg-induced Ca2+ elevations and reduced the amount of Ca2+ released into the cytosol. Depletion of the smooth endoplasmic reticulum (SER) Ca2+ pool with thapsigargin or down-regulation of muscarinic receptors and inositol-1,3,4-triphosphate (IP3) receptors with bethanechol (BCh) caused similar reductions in the amplitude of the MeHg-induced Ca2+ increase, suggesting that MeHg interacts with muscarinic receptors to cause Ca2+ release from the SER through activation of the IP3 receptors. To determine whether this Ca2+ release plays a role in MeHg-induced cell death, cells were exposed to MeHg in the presence of specific muscarinic receptor inhibitors. Acute exposure to increasing concentrations of MeHg (0.2-1.0 microM) caused a corresponding increase in cell death at 24.5 h post-exposure. Prior down-regulation of muscarinic and IP3receptors with BCh protected against cell death. Protection was ablated by atropine and the M3 receptor antagonist 4-diphenylacetoxyl-N-methylpiperidine methiodide (DAMP), but not by the neuronal nicotinic receptor antagonist dihydro-beta-erythroidine hydrobromide (DHE). Thus activation of M3 muscarinic receptors with subsequent generation of IP3 evidently contributes to elevated [Ca2+]i and subsequent cytotoxicity of cerebellar granule cells by MeHg.
authors.affiliation: Department of Pharmacology and Toxicology, Institute for Environmental Toxicology, and Neuroscience Program, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Tobi L
authors.initials: TL
authors.lastname: Limke
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Bearss
authors.forename: William D
authors.initials: WD
authors.lastname: Atchison
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects*; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008297:Male; D008767:Methylmercury Compounds / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043587:Receptor, Muscarinic M3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004785:Environmental Pollutants; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008767:Methylmercury Compounds; D043587:Receptor, Muscarinic M3; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D010738:Type C Phospholipases; C004925:methylmercuric chloride; D002118:Calcium