Figure 3-32 Cross-section of a schematized γ-aminobutyric acid (GABA)-benzodiazepine receptor complex, which is a prototypical ligand-gated ion channel complex. Binding of benzodiazepine agonists to the GABA_A ligand-gated ion channel facilitates the action of endogenous GABA. This results in increased inhibitory chloride ion flux in the central nervous system. A, Schematic drawing of the GABA_A ligand-gated ion channel complex shows the receptor sites for benzodiazepines and GABA, as well as distinct receptor sites for barbiturates and alcohol. B, Model of the GABA_A receptor and chloride ion channel shows that the protein complex is composed of a hetero-oligomer of five subunits, including α, β, γ, and δ or ρ polypeptides. Each subunit has four putative membrane-spanning domains (numbered 1 through 4 and represented by cylinders). (A, from Berkowitz DE: Cellular signal transduction. In Schwinn DA [ed]: Scientific Principles of Anesthesia, vol 2. Philadelphia, Current Medicine, 1998; B, adapted from Firestone L, Quinlan J, Gyulai F: Mechanisms of anesthetic action. In Schwinn DA [ed]: Scientific Principles of Anesthesia, vol 2. Philadelphia, Current Medicine, 1998.)