Regulates the activity of L-type calcium channels that contain CACNA1C as pore-forming subunit (By similarity). 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 slowing their rates of activation, deactivation and desensitization and by mediating their resensitization. Does not show subunit-specific AMPA receptor regulation and regulates all AMPAR subunits. {ECO:0000250|UniProtKB:Q8VHW2, ECO:0000269|PubMed:20805473, ECO:0000269|PubMed:21172611}. This is the function of ENSG00000142408 (CACNG8, calcium voltage-gated channel auxiliary subunit gamma 8).