The auxiliary subunits Neto1 and Neto2 reduce voltage-dependent inhibition of recombinant kainate receptors.

Kainate receptors can be subject to voltage-dependent block by intracellular polyamines, which causes inward rectification of the current-voltage relationship. Sensitivity to polyamine block is largely determined by the identity of a residue within the pore domain that can be altered through RNA editing. This process causes replacement of the encoded glutamine(Q) with a positively charged arginine(R), eliminating polyamine inhibition and thus inward rectification. In neurons, kainate receptors can associate with the auxiliary subunits Neto1 or Neto2. These transmembrane proteins alter the trafficking, channel kinetics, and pharmacology of the receptors in a subunit-dependent manner. We found that coexpression of Neto subunits with recombinant GluK2(Q) kainate receptors greatly reduced inward rectification without altering calcium permeability. This effect was separate from modulation of channel kinetics, as mutations within the extracellular LDLa domain of the Neto proteins completely eliminated their effects on desensitization but only reduced their effects on rectification. Conversely, deletion of the intracellular C-terminal domain of Neto1 or Neto2 or neutralization of positively charged residues within this domain prevented the reduction in rectification but did not alter effects on channel kinetics. These results demonstrate new roles for Neto1 and Neto2 in regulating kainate receptor function and identify domains within these auxiliary subunits important for mediating their effects.