Previous studies have shown the number of TARPs per AMPA receptor complex could be variable (Kim et al., 2010 and Shi et al., 2009). Future studies are needed to define the stoichiometry of both TARPs and CNIH-2 within native AMPA receptor complexes. These studies provide important new insights regarding AMPA receptor function. Whereas previous biochemical studies suggested that TARPs and CNIH-2/3 interact predominantly with independent pools of AMPA receptors, our results

reveal crucial cooperative selleck screening library interactions. CNIH-2 can promote surface expression of GluA subunits in transfected cells (Schwenk et al., 2009), but this has not been definitively demonstrated in hippocampal neurons. The dramatic loss of extrasynaptic AMPA receptors in γ-8 knockout mice (Fukaya et al., 2006 and Rouach et al., 2005) suggests that CNIH-2

cannot efficiently traffic AMPA receptors in these neurons. Of note, CNIH proteins lack a synaptic-targeting PDZ binding site and, in this study, we found that CNIH-2 could not rescue synaptic AMPA receptors in stargazer granule cells. While this work was under final review, Shi et al. (2010) also found that CNIH-2 can partially restore extrasynaptic but not synaptic AMPA receptor function in cerebellar granule cells from homozygous or heterozygous stargazer mice. On the other hand, we find that CNIH-2 can synergize selleckchem with γ-8 to augment synaptic AMPA receptor function in homozygous stargazer cerebellar granule neurons. Thus, multiple classes of auxiliary subunits acting on a common GluA tetramer provide a combinatorial layer of complexity for regulation of AMPA receptors in diverse cell types and physiological conditions. Previous studies showed that CNIH protein from both vertebrates and invertebrates mediate endoplasmic reticulum (ER) export of specific growth factors (Hoshino et al., 2007 and Roth et al., 1995). It is therefore possible that CNIH-2 transiently interacts with γ-8-containing AMPA receptor complex solely within the ER to modulate function. Indeed, Shi

Rolziracetam et al. found that overexpressed CNIH-2 accumulates in the Golgi apparatus and does not occur on the neuronal surface (Shi et al., 2010). However, our subcellular fractionation studies indicate that endogenous CNIH-2 is enriched in synaptosomes and is particularly concentrated together with TARPs and AMPA receptors in postsynaptic densities. In addition, electron microscopic data reveal CNIH-2/3 immunoreactivity at postsynaptic sites in hippocampal CA1 neurons (Schwenk et al., 2009). Furthermore, our characterization of neuronal AMPA receptor resensitization and kainate/CTZ pharmacology, together with our analysis of synaptic AMPA receptor gating in hippocampal and stargazer cerebellar granule neurons, suggests that CNIH-2 associates with synaptic and extra-synaptic γ-8-containing AMPA receptors.