Regulates the trafficking and gating properties of AMPA-selective glutamate receptors (AMPARs). Promotes their targeting to the cell membrane and synapses and modulates their gating properties by regulating their rates of activation, deactivation and desensitization. Blocks CACNG8-mediated resensitization of AMPA receptors. Acts as an auxiliary subunit for AMPA-selective glutamate receptors (AMPARs). Found in a complex with GRIA1, GRIA2, GRIA3, GRIA4, CNIH3, CACNG2, CACNG3, CACNG4, CACNG5, CACNG7 and CACNG8. Interacts with GRIA1 (By similarity). Interacts with CACGN8. Also localizes to the cell membrane of extrasynaptic sites (dendritic shafts, spines of pyramidal cells). Brain. Highest levels seen in the hippocampus, intermediate levels in the cerebral cortex, striatum olfactory bulb, and thalamus and lower levels in the cerebellum (at protein level). Also expressed in the lung. First detected at the eight-cell stage. Expressed in eight-cell embryo, blastocyst, 6.5-day whole embryo, 7.5-day primitive streak, 11.5-day limb bud and in 13.5-day whole embryo. Belongs to the cornichon family.