The amino acid γ-aminobutyric acid (GABA) is an inhibitory neurotransmitter that acts through two families of heteromeric ligand-gated ion channels, GABAA and GABAC and a G protein-coupled receptor, GABAB. Muscimol is a full GABAA agonist and partial GABAC agonist. It binds GABAA on both high- and low-affinity sites (Kd = 10 and 270 nM, respectively), stimulating chloride efflux with an EC50 value of 200 nM. Benzodiazepines enhance the effects of muscimol via GABAA without altering its binding. Muscimol activates GABAC receptors with an EC50 value of 1.3 μM. It also acts as an inhibitor of GABAA uptake and a substrate for the GABA-metabolizing enzyme GABA transaminase. Muscimol impairs memory formation and retrieval in mice and attenuates airway constriction in guinea pigs in vivo.
