Methyl mercury increases intracellular Ca2+ and inositol phosphate levels in cultured cerebellar granule neurons.
In an effort to explain the previously observed methyl mercury (MeHg)-induced stimulation of protein phosphorylation in cerebellar granule neuron cultures, the effect of MeHg on protein kinase activities in cell-free assays and on second messenger systems in cultured neurons has been examined. Using cell-free assays for several protein kinases, no stimulation of enzyme activity was found at any concentration of MeHg tested. After 24 h exposure, 1-5 microM MeHg was found to have no significant effect on neuronal cyclic AMP levels. In contrast, intracellular levels of Ca2+ and rates of 45Ca2+ uptake were elevated 2.2-fold and 3.6-fold, respectively, by 5 microM MeHg. These effects were not observed with mercuric chloride, triethyllead, or lead acetate. Measurement of inositol phosphate production in granule cell cultures revealed a sensitive, pretoxic effect of MeHg with twofold stimulation following 30-min exposure to 5 microM MeHg and 1.6-fold after 24-h exposure to 3 microM MeHg. Detection of inositol phosphate production after 30 min of MeHg was largely neuron-specific. These results suggest that second messenger-mediated activation of select protein kinase enzymes may be the mechanism underlying MeHg-induced stimulation of protein phosphorylation in cerebellar neuronal culture. In addition, these findings indicate a specific interference with neuronal signal transduction and suggest a basis for the selective neurotoxic action of this agent.
Department of Pathology (Neuropathology), UCLA Center for Health Sciences 90024.
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D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D008767:Methylmercury Compounds / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015290:Second Messenger Systems / Q000187:drug effects
D002132:Calcium Radioisotopes; D007295:Inositol Phosphates; D008767:Methylmercury Compounds; D047428:Protein Kinase Inhibitors; D000001:Calcimycin; D000242:Cyclic AMP; D011494:Protein Kinases; C004925:methylmercuric chloride; D002118:Calcium