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  • Nickel modulates the electrical activity of cultured cortical neurons through a specific effect on N-methyl-D-aspartate receptor channels. 21182900

    Nickel (Ni(2+)) is a toxic metal that affects the function of several ionic channels. In the N-methyl-d-aspartate (NMDA) subtype of glutamate receptor (NR), it causes activity enhancement of the channels containing the NR2B subunit and voltage-independent inhibition of those containing NR2A. Thus, it may represent a functional marker for the identification of NR native channel subunits. We investigated the effect of Ni(2+) on spontaneous NR currents in cortical neurons, dissociated from 18-day rat embryos and maintained in culture for up to ∼40 days. In whole-cell voltage-clamp at -60 mV, in a Mg(2+)-free bath containing the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) (10 μM), spontaneous currents were blocked by 10 μM D(-)-2-Amino-5-phosphonopentanoic acid (APV) (10 μM), and by NR2B antagonists, ifenprodil (10 μM) or Ro25-6981 (Ro25, 1 μM), indicating that they are due to NRs containing predominantly the NR2B subunit. In the presence of Ni(2+) (30 μM) the amplitude and the frequency of spontaneous currents were increased and the decay time decreased. A higher dose (300 μM) blocked all electrical activity. In current-clamp, Ni(2+) (30 μM) caused a ∼5 mV reversible depolarization. The effect of Ni(2+), as well as that of NR2B antagonists, was almost independent of days in vitro (DIV) in the range from 18 to 33 DIV. The electrical activity of the neuronal networks measured by microelectrode arrays (MEAs) was also affected by Ni(2+), which caused a decrease in firing rate, but an increase in burst duration, while Ro25 (1-10 μM) caused a decrease in both firing rate and burst duration. Finally, reverse transcription polymerase chain reaction (RT-PCR) revealed a predominant expression of NR2B, with no modification during DIV. These results demonstrate that, in these cultured cells, the NR spontaneous current is almost entirely due by NR2B-containing receptors and that Ni(2+) affects the electrical activity through a specific effect on NR channels.
    Document Type:
    Reference
    Product Catalog Number:
    MAB5574

  • Nickel compounds induce histone ubiquitination by inhibiting histone deubiquitinating enzyme activity. 18279901

    Nickel (Ni) compounds are known carcinogens but underlying mechanisms are not clear. Epigenetic changes are likely to play an important role in nickel ion carcinogenesis. Previous studies have shown epigenetic effects of nickel ions, including the loss of histone acetylation and a pronounced increase in dimethylated H3K9 in nickel-exposed cells. In this study, we demonstrated that both water-soluble and insoluble nickel compounds induce histone ubiquitination (uH2A and uH2B) in a variety of cell lines. Investigations of the mechanism by which nickel increases histone ubiquitination in cells reveal that nickel does not affect cellular levels of the substrates of this modification, i.e., ubiquitin, histones, and other non-histone ubiquitinated proteins. In vitro ubiquitination and deubiquitination assays have been developed to further investigate possible effects of nickel on enzymes responsible for histone ubiquitination. Results from the in vitro assays demonstrate that the presence of nickel did not affect the levels of ubiquitinated histones in the ubiquitinating assay. Instead, the addition of nickel significantly prevents loss of uH2A and uH2B in the deubiquitinating assay, suggesting that nickel-induced histone ubiquitination is the result of inhibition of (a) putative deubiquitinating enzyme(s). Additional supporting evidence comes from the comparison of the response to nickel ions with a known deubiquitinating enzyme inhibitor, iodoacetamide (IAA). This study is the first to demonstrate such effects of nickel ions on histone ubiquitination. It also sheds light on the possible mechanisms involved in altering the steady state of this modification. The study provides further evidence that supports the notion that nickel ions alter epigenetic homeostasis in cells, which may lead to altered programs of gene expression and carcinogenesis.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple