The open channel blocking drug, IEM-1460, reveals functionally distinct α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors in rat brain neurons

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The properties of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors were examined in various cell types isolated from young rat hippocampus, striatum and cerebellum using patch-clamp and fast application techniques. A dicationic adamantane derivative, IEM-1460, reversibly inhibited kainate-induced currents. In the presence of 100 μM IEM-1460, kainate currents in striatal giant cholinergic interneurons and hippocampal non-pyramidal neurons were inhibited by 95% and 81%, respectively, at V h=−70 mV. Striatal GABAergic principal cells, hippocampal pyramidal neurons and cerebellar Purkinje cells had low sensitivity to IEM-1460 (inhibition by 4–15%). Analysis of averaged data from the cell types studied revealed a highly significant positive correlation ( r=0.93, P<0.01) between percentage inhibition by 100 μM IEM-1460 and relative calcium permeability of AMPA receptors, P Ca/ P Na. Also, within each brain structure, the sensitivity of IEM-1460 block was lower the stronger the outward rectification of kainate currents. Some hippocampal neurons exhibited intermediate sensitivity to IEM-1460. Kainate currents were suppressed by 40% in the presence of 100 μM IEM-1460. Meanwhile, AMPA receptors in this cell type had low calcium permeability ( P Ca/ P Na=0.13) and demonstrated outwardly rectifying kainate currents. The interrelation of different properties of AMPA receptors considering their assembly is discussed. The data obtained suggest that IEM-1460 may be a convenient and promising marker of native AMPA receptor assembly: it selectively inhibits Ca 2+-permeable, GluR2-lacking AMPA receptors.