Transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor regulatory proteins (TARPs) are tetra-membrane-spanning proteins with a weak homology to the γ subunit of L-type voltage-dependent Ca²⁺ channel (γ-1). Previous results have suggested that TARPs may play an important role in the regulation of AMPA receptor trafficking to synaptic plasma membrane. A TARP family member, γ-8, which is highly expressed in the hippocampus, has a unique, long C-terminal tail. In this study, we have attempted to identify novel proteins that may regulate trafficking of γ-8 by direct or indirect protein interactions. Recently, we demonstrated that a Ca²⁺/calmodulin-dependent Ser/Thr phosphatase, calcineurin/PP2B co-immunoprecipitated with anti-γ-8 antibody from Triton X-100-solubilized rat hippocampal P2 fractions. To identify additional γ-8-interacting proteins, co-immunoprecipitation experiments were performed from the milder detergent, CHAPS-solubilized rat hippocampal P2 fractions and the γ-8-containing complexes were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Here we have identified 20 potential binding proteins of TARP γ-8. These are 7 membrane-spanning proteins [AMPA receptors (GluA1, GluA2, GluA3, GluA4), syntaxin 1, syntaxin 7 and proline-rich transmembrane protein 1] and 13 intracellular proteins [actin, tubulin, HSP70, HSP72, NSF, munc18, PSD-95, CRMP1, CRMP2, V-ATPase subunit A, Goα, GAPDH and importin β1]. To confirm the interaction of γ-8 with three proteins [syntaxin 1, CRMP2 and importin β1], we performed co-immunoprecipitation experiments using transiently transfected HEK293 cells. Syntaxin 1 and importin β1, not CRMP2 were co-immunoprecipitated with γ-8 from transfected HEK293 cell lysates. These results indicate that syntaxin 1 and importin β1 interact directly with γ-8 and may regulate the biological activity of AMPA receptor-γ-8 complex.