Transmitter-gated ion channels

Johnston, GA (1996) GABAc receptors relatively simple transmitter-gated ion channels Trends... 

Smart, T. G. Regulation of excitatory and inhibitory neuro-transmitter-gated ion channels by protein phosphorylation. Curr. Opin. Neurobiol. 7 358-367,1997. 

Transmitter-gated ion channel Voltage-activated Na+ channel Voltage-activated Ca + channel... 

When comparing transmitter-gated ion channels on a functional level, one can discern between anion and cation channels. The former ones comprise the GABAa and glycine receptors, which display a rank order of anion selectivity of I- > Hr > Cl- and which are also permeable to HC()3. All other ionotropic receptors mentioned here are cation channels, which discriminate rather poorly between various monovalent cations, at least when compared with voltage-gated ion channels. Some... 

E. Barnard. Receptor classes and the transmitter gated ion channels. Trends Biochem. ScL /7 368-374 (1992). 

Synaptic Transmission. Figure 1 Synaptic transmission. The presynaptic terminal contains voltage-dependent Na Superscript and Ca2+ channels, vesicles with a vesicular neurotransmitter transporter VNT, a plasmalemmal neurotransmitter transporter PNT, and a presynaptic G protein-coupled receptor GPCR with its G protein and its effector E the inset also shows the vesicular H+ pump. The postsynaptic cell contains two ligand-gated ion channels LGIC, one for Na+ and K+ and one for Cl-, a postsynaptic GPRC, and a PNT. In this synapse, released transmitter is inactivated by uptake into cells. 

Of the several classes of receptors for endogenous chemical signals [3], two are used as postsynaptic receptors in synaptic transmission ligand-gated ion channels (LGICs) and G protein-coupled receptors (GPCRs Fig. 1). Due to the large number of transmitters and the existence of several receptor types for almost all, postsynaptic receptor activation is the most diversified step of synaptic transmission. Table 1 shows selected neurotransmitter receptors. 

Ionotropic receptors (bottom left) are ligand-gated ion channels. When they open as a result of the transmitter s influence, ions flow in due to the membrane potential (see p. 126). If the inflowing ions are cations (Na"", C, Ca ""), depolarization of the membrane occurs and an action potential is triggered on the surface of the postsynaptic cell. This is the way in which stimulatory transmitters work (e.g., acetylcholine and glutamate). By contrast, if anions flow in (mainly Cl ), the result is hyperpolarization of the postsynaptic membrane, which makes the production of a postsynaptic action potential more dif cult. The action of inhibitory transmitters such as glycine and GABA is based on this effect. 

Ionotropic receptors are ligand-gated ion channels (left half of the table). The receptors for stimulatory transmitters (indicated in the table by a ) mediate the inflow of cations (mainly Na""). When these open after binding of the transmitter, local depolarization of the postsynaptic membrane occurs. By contrast, inhibitory neurotransmitters (GABA and glycine) allow cr to flow in. This increases the membrane s negative resting potential and hinders the action of stimulatory transmitters hyperpolarization, 0). 

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