title: Inorganic lead may inhibit neurite development in cultured rat hippocampal neurons through hyperphosphorylation.
abstract: Inorganic lead inhibits neurite initiation in cultured rat hippocampal neurons at concentrations as low as 100 nM. Conflicting reports suggest that Pb2+ may stimulate or inhibit protein kinase C, adenylyl cyclase, phosphodiesterase, and calmodulin, or increase intracellular free Ca2+ concentrations. Therefore, Pb2+ may alter the activities of Ca2+/calmodulin-dependent protein kinase (CaM kinase) or protein kinases C or A. We cultured rat hippocampal neurons in 100 nM PbCI2 alone or in combination with kinase or calmodulin inhibitors. Inhibiting protein kinase C with calphostin C exacerbated the inhibition of neurite initiation caused by PbCI2, but inhibiting protein kinase A with KT5720, CaM kinase with KN62, or calmodulin with calmidazolium completely reversed the effects of PbCI2. These results indicate that Pb2+ may inhibit neurite initiation by inappropriately stimulating protein phosphorylation by CaM kinase or cyclic AMP-dependent protein kinase (PKA), possibly by stimulating calmodulin. This hypothesis is supported by findings that other treatments that should increase protein phosphorylation (okadaic acid, a protein phosphatase inhibitor, and Sp-cAMPS, a PKA activator) also reduced neurite initiation. Whole-cell intracellular free Ca2+ ion concentrations were not significantly altered by 100 nM PbCI2 at 4, 12, 24, or 48 hr. Therefore, the hypothesized stimulatory effects of Pb2+ exposure on calmodulin, CaM kinase, or PKA are probably not caused by increases in whole-cell intracellular free Ca2+, but may be attributable either to intracellular Pb2+ or to localized increases in [Ca2+]in that are not reflected in whole-cell measurements.
authors.affiliation: Biology Department, University of Colorado at Denver 80217-3364, USA.
authors.forename: M
authors.initials: M
authors.lastname: Kern
authors.forename: G
authors.initials: G
authors.lastname: Audesirk
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D007854:Lead / Q000633:toxicity*; D016501:Neurites / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002147:Calmodulin; D047428:Protein Kinase Inhibitors; D007854:Lead; D002118:Calcium