In the present study we have generated conditional CNIH-2 and CNIH-3 knockout (KO) mice to determine the roles of CNIH-2 and -3 in excitatory synaptic transmission in the hippocampus. We find that CNIHs play a critical role in supporting AMPAR-mediated responses, as AMPAR function is profoundly reduced in neurons lacking both CNIH-2 and -3. However, importantly, CNIH-2/-3 binding to AMPARs is dependent on AMPAR subunit composition and TARPs. Four subunits (GluA1-GluA4) contribute to the formation of tetrameric AMPARs. We have previously shown that ~80% of synaptic AMPARs in CA1 pyramidal neurons are composed of GluA1A2 heteromers, while the rest are GluA2A3 heteromers (Lu et al., 2009). Here our data reveal that CNIH-2/-3 selectively binds to GluA1 in hippocampal neurons, allowing GluA1A2 receptors to reach the surface, and suggest that CNIH-2/-3 interaction with non-GluA1 subunits is prevented by γ-8. Removal of CNIH-2/-3 also speeds up the deactivation kinetics of surface AMPARs, an effect attributable to the loss of GluA1A2 receptors, which deactivate more slowly than GluA2A3 receptors. Thus our data point to a model in which the trafficking and gating of individual AMPARs are determined by the interplay of AMPAR subunits, cornichons and TARPs.
