Abstract

Fast excitatory synaptic transmission in the mammalian central nervous system is mediated by glutamate activated AMPA receptors (AMPARs). The core GluA subunits of AMPARs in neurons co-assemble with auxiliary subunits, including transmembrane AMPAR regulatory proteins (TARPs), several of which modifiy AMPA receptor-channel gating kinetics. In the case of AMPARs containing four copies of TARP γ8, achieved by expression of the tandem GluA2Q∗TARPγ8 subunit developed in the lab, AMPARs exhibit resensitization, or partial recovery from desensitization in continued presence of glutamate. We have recorded single channel currents in cell-attached patch recordings and show that under resensitizing conditions, these AMPARs show transitions primarily from closed to higher conductance levels, similar to activation of homomeric GluA receptors in the presence of cyclothiazide. To study the conformation associated with these states we used single molecule FRET and show that this high conductance state produced by GluA2Q∗TARPγ8 channels exhibits tighter coupling between subunits in the extracellular parts of the receptor.

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