Despite its importance in the cerebellum, the functions of the orphan glutamate receptor δ2 are unknown. We examined a mutant δ2 receptor channel in lurcher mice that was constitutively active in the absence of ligand. Because this mutation was within a highly conserved motif (YTANLAAF), we tested its effect on several glutamate receptors. Mutant δ2 receptors showed distinct channel properties, including double rectification of the current- voltage relationship, sensitivity to a polyamine antagonist and moderate Ca2+ permeability, whereas other constitutively active mutant glutamate channels resembled wildtype channels in these respects. Moreover, the kinetics of ligand-activated currents were strikingly altered. We conclude that the δ2 receptor has a functional ion channel pore similar to that of glutamate receptors. The motif may have a role in the channel gating of glutamate receptors.
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