Ion channels chemical-gated

Neurotransmitter receptors are membrane proteins that provide a binding site that recognizes and responds to neurotransmitter molecules. Some receptors, such as the postsynaptic receptors of nerve or muscle, are directly linked to membrane ion channels thus, binding of the neurotransmitter occurs rapidly (within fractions of a millisecond) and directly affects ion permeability (Figure 3.7A). The effect of neurotransmitters on these chemically gated ion channels is discussed on p. 82. 

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. 

Three families of serotonin receptor, the 5-HT family, the 5-HT2 family and the family that includes the 5-HT4, 5-ht6 and 5-HT7 receptors represent the three major classes of 5-HT receptor that are G-protein-coupled receptors (Ch. 19). The 5-HT3 receptor is a ligand-gated ion channel and is a separate family. Although each serotonin receptor can be potently activated by 5-HT, differences insignal transduction mechanisms,neuroanatomical distribution and affinities for synthetic chemicals create opportunities for drug discovery and make each 5-HT receptor subtype a potential therapeutic target. 

Finally, there are ion channels that respond to intracellular (as opposed to extracellular or environmental) chemical stimuli. These form part of cellular signaling pathways and may be opened by cellular messengers such as calcium ion, Ca +. Such channels are known as signal-gated ion channels. 

Gated ion channels of the plasma membrane that open and close (hence the term gating ) in response to the binding of chemical ligands or changes in transmembrane potential. These are the simplest signal transducers. The acetylcholine receptor ion channel is an example of this mechanism (Section 12.2). 

The membrane of the neuron is differentially specialized. The membrane of the soma and dendrites is designed to react to chemical stimuli and contains both neurotransmitter-gated ion channels and neurotransmitter-gated receptors associated... 

Very recently, we reviewed the role of membrane action of flavonoids. The structure of flavonoids enables specific interactions with different membrane proteins (multidrug transporters, voltage-gated and chemically activated ion channels) and also nonspecific interactions with the lipid phase of membranes [8]. 

For any chemical messenger to elicit an effect it must first be recognised by the cell. Peptide messengers interact with cell-surface receptors (peptides do not cross the membrane), whereas steroid- and lipid-derived messengers diffuse across the cell membrane and interact with intracellular receptors. Ligand-gated ion-channel receptors are a class of receptor that may occur either at the cell surface or within the cell. 

---