GABA A (γ-aminobutyric acid-type A) receptors are members of the cysteine-loop family of neurotransmitter-gated ion channels. GABA binding to A-type receptors induces anion-selective ion channel opening. These receptors are the principal fast inhibitory neurotransmitter receptors in the CNS. GABA A receptors are heteropentamer combinations of seven subunit types; α, β, γ, δ, ε, θ, and π. Three subunits, α, β, and γ, have at least three separate gene products in mammals, and typical GABA A receptors have some combination of α, β, and γ subunits.
In select neurons, however, a δ subunit replaces the γ subunit. It would appear that δ subunits have a preference for various α-β combinations. In cerebellar granule cells, the δsubunit contributes to a unique α6/β/δ heteromer. δ subunit receptors may function to limit the spread of excitatory impulses to dendritically-complexed neurons. They also appear to be sensitive to steroid modulation. The rat δ subunit is a 50 kDa, 433 amino acid (aa), 4 transmembrane protein with two terminal extracellular regions. The ligand-binding region is in the N-terminus (aa 4 - 246). The rat and mouse N-terminal extracellular domains (ECD) (aa 17 - 248) are 99% aa identical; the mouse and human ECD are 95% aa identical.