Regulates the activity of L-type calcium channels that contain CACNA1C as pore-forming subunit (PubMed:21127204). Regulates the trafficking and gating properties of AMPA-selective glutamate receptors (AMPARs), including GRIA1 and GRIA4. Promotes their targeting to the cell membrane and synapses and modulates their gating properties by slowing their rates of activation, deactivation and desensitization and by mediating their resensitization (PubMed:21172611). Interacts with CACNA1C. Identified in a complex with the L-type calcium channel subunits CACNA1C, CACNA2D1 and either CACNB1 or CACNB2 (PubMed:21127204). Acts as an auxiliary subunit for AMPA-selective glutamate receptors (AMPARs) (PubMed:21172611). Interacts with GRIA1 (PubMed:21172611). Detected in heart left ventricle. Belongs to the PMP-22/EMP/MP20 family. CACNG subfamily.