AMPAR/TARP stoichiometry differentially modulates channel properties

AMPARs control fast synaptic communication between neurons and their function relies on auxiliary subunits, which importantly modulate channel properties. Although it has been suggested that AMPARs can bind to TARPs with variable stoichiometry, little is known about the effect that this stoichiometry exerts on certain AMPAR properties. Here we have found that AMPARs show a clear stoichiometry dependent modulation although AMPARs still need to be fully saturated with TARPs to show some typical TARP-induced characteristics (i.e. an increase in channel conductance). We also have uncovered important differences in the stoichiometric modulation between calcium-permeable and calcium-impermeable AMPARs. Moreover, in heteromeric AMPARs, TARP positioning in the complex is important to exert certain TARP-dependent features. Finally, by comparing data from recombinant receptors with endogenous AMPAR currents from cerebellar granule cells, we have determined a likely functional stoichiometry of 2 TARPs associated with GluA2 subunits in the somatic AMPARs found in this cell type.