Transmembrane AMPA receptor regulatory proteins (TARPs) serve as auxiliary subunits of AMPA receptors that regulate functional aspects of these receptors such as: fast excitatory synaptic transmission, surface trafficking, enhancing synaptic clustering and increasing glutamate affinity. Generally, TARPs are responsible for regulating expression, channel properties and localization of AMPA receptors in the brain¹.

TARPs are non-pore-forming integral membrane proteins with four transmembrane domains that are widely expressed in the CNS. 

The TARP family is divided in Type I and type II subfamily. Type I TARPs comprise four calcium channel γ subunits: γ2, γ3, γ4, and γ-8, also known as Cacng2, 3, 4 and 8, respectively^2,3.

γ-8 TARP predominantly expressed in the telencephalon with abundant distribution on hippocampal excitatory synapses and extrasynaptic membranes. It is expressed in low levels in newborn and neonatal brain and can be found in higher levels in adult brain⁴. γ-8 plays an important role in increasing the number of synaptic and extrasynaptic AMPA receptors on dendrites and spines⁵. 

The C terminus of γ-8 contains 3 unique stretches of amino acids that are not found in any of the other TARPs. In addition, it contains PDZ-binding motifs². In heterologous cells, γ-8 prolong the current rise time in response to small amounts of glutamate and slow GluA1 receptor desensitization and deactivation³.

Several studies have shown that overexpression of TARP γ-8 increases the number of AMPARs in the plasma membrane. In γ-8 knockout mice, AMPA receptor expression is severely reduced from the synaptic and extrasynaptic membranes of dendrites and does not progress through the secretory pathway^5,6_.