GABA receptor

The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid (GABA), the chief inhibitory in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABA_A and GABA_B.

GABA_A receptors are ligand-gated ion channels (also known as ionotropic receptors), whereas GABA_B receptors are G protein-coupled receptors (also known as metabotropic receptors).

Ligand-gated ion channels: GABA_A

It has long been recognized that the fast response of neurons to GABA that is blocked by bicuculline and picrotoxin is due to direct activation of an anion channel. This channel was subsequently termed the GABA_A receptor. Fast-responding GABA receptors are members of family of Cys-loop ligand-gated ion channels. Members of this superfamily, which includes nicotinic acetylcholine receptors, GABA_A receptors, glycine and 5-HT₃ receptors, possess a characteristic loop formed by a disulfide bond between two cysteine residues.

In ionotropic GABA_A receptors, binding of GABA molecules to their binding sites in the extracellular part of the receptor triggers opening of a chloride ion-selective pore. The increased chloride conductance drives the membrane potential towards the reversal potential of the Cl¯ ion which is about –65 mV in neurons, inhibiting the firing of new action potentials. This mechanism is responsible for the sedative effects of GABA_A allosteric agonists.