GABAC

GABAC, commonly referred to as the GABA_C receptor or GABA_A-ρ receptor, is a ligand-gated ion channel that mediates inhibitory neurotransmission in the central nervous system. It is formed primarily by rho subunits, specifically rho1, rho2, and rho3, which are encoded by the GABRR1, GABRR2, and GABRR3 genes in humans. The term GABAC is often used to describe receptors assembled from these rho subunits, which were once thought to be a distinct class but are now generally classified under the GABA_A receptor family as GABA_A-ρ receptors.

Structure and pharmacology: GABA_A-ρ receptors assemble as homomeric channels composed of rho subunits. They form chloride-permeable channels that open in response to GABA binding, producing hyperpolarization and inhibition of neuronal activity. Pharmacologically, GABA_A-ρ receptors have unique properties: they are typically insensitive to benzodiazepines and many classical GABA_A receptor modulators, and they respond differently to certain antagonists. They are relatively resistant to bicuculline, a typical GABA_A receptor antagonist, and can be inhibited by chloride channel blockers such as picrotoxin.

Distribution and function: GABA_A-ρ receptors are prominently expressed in the retina, where they contribute to inhibitory signaling in retinal circuits, and are present in various brain regions as well. Their currents tend to desensitize more slowly than some GABA_A receptor currents, allowing broader temporal influence on synaptic signaling. Through chloride conductance, they help shape visual processing and overall neuronal excitability.

Taxonomy and naming: because of evolving understanding of subunit composition and pharmacology, GABAC is often described within the broader GABA_A receptor classification as GABA_A-ρ receptors. The rho subunits are encoded by GABRR1, GABRR2, and GABRR3 genes, and the receptor is distinct from conventional GABA_A receptors that utilize alpha, beta, and gamma subunits.