Figure 4-14 A, The neurotransmitters γ-aminobutyric acid (GABA) and glycine are released at inhibitory synapses, bind to their respective receptors, and result in a flow of chloride ions across the postsynaptic membrane. B, Inhaled anesthetics potentiate the postsynaptic inhibition produced by GABA or glycine. C, Inhibitory receptor-channel complexes, as well as many other ligand-gated channels, typically consist of five subunits embedded in a membrane lipid bilayer. Many subunit combinations may exist for a given receptor-channel complex. D, Each of the subunits contains four transmembrane segments, and the second transmembrane segment of each subunit is thought to line a pore (i.e., channel) that extends across the membrane. Anesthetic sensitivity can be altered by mutation of critical amino acids in these transmembrane regions. (Adapted from Franks NP, Lieb WR: Anaesthetics set their sites on ion channels. Nature 389:334, 1997.)