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Block of open channels of recombinant AMPA receptors and native AMPA/kainate receptors by Adamantane derivatives

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Abstract

  • 1The effects of two adamantane derivatives, 1-trimethylammonio-5-(l-adamantane-methylammoniopentane dibromide) (IEM-1460) and 1-ammonio-5-(l-adamantane-methylammoniopentane dibromide) (IEM-1754) on kainate-induced currents were studied in Xenopus oocytes expressing recombinant ionotropic glutamate receptors and in freshly isolated neurones from rat hippocampal slices.
  • 2The adamantane derivatives caused use-and voltage-dependent block of open channels of recombinant AMPA receptors. This antagonism was dependent on receptor subunit composition; channels gated by recombinant, homomeric GluRl and GluR3 receptors exhibited a higher sensitivity to block than those gated by receptors containing edited GluR2 subunits. In the former cases, IEM-1460 had an IC50 of 1.6 μm at a holding potential (Vh) of −80 mV and IEM-1754 was 3.8 times less potent than IEM-1460. In contrast, 100 μm IEM-1460 inhibited responses to 100 μm kainate of receptors containing edited GluR2 subunits by only 7.8 ± 2.4% (n= 5 oocytes) at a Vh of −80 mV.
  • 3Native AMPA/kainate receptors in isolated hippocampal cells were inhibited by adamantane derivatives in a use- and voltage-dependent manner. This antagonism was dependent on cell type: pyramidal neurones were less sensitive to IEM-1460 (IC50= 1617 μm at Vh=−80mV) than interneurones (IC50= 1.6 μm at Vh=−80 mV). IEM-1460 and IEM-1754 were equipotent when applied to pyramidal neurones, but IEM-1754 was less potent (∼3 times) than IEM-1460 when applied to interneurones.
  • 4It is concluded that the presence of the edited GluR2 subunit in recombinant AMPA receptors and native AMPA/kainate receptors inhibits channel block by organic cations and that adamantane derivatives are potentially valuable tools for identifying classes of AMPA/kainate receptors and their roles in synaptic transmission.

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