Sodium channel chemically gated

Once an electrical impulse invades the presynaptic axon terminal, it causes the release of chemical neurotransmitter stored there (Fig. 1—3). Electrical impulses open ion channels, such as voltage-gated calcium channels and voltage-gated sodium channels, by changing the ionic charge across neuronal membranes. As calcium flows into the presynaptic nerve, it anchors the synaptic vesicles to the inner membrane of the nerve terminal so that they can spill their chemical contents into the synapse. The way is paved for chemical communication by previous synthesis and storage of neurotransmitter in the first neuron s presynaptic axon terminal. 

Batrachotoxin is an important research tool because of its action of holding voltage-gated sodium channels open as well as its specific effects at other ligandbinding sites. It was previously used commonly in channel and ligand research. There are no commercially available stocks of batrachotoxins, however, and work in Colombia is currently difficult or impossible, so these chemicals are used less frequently in research. 

One of the most important chemical classes of insecticides are the pyrethroids, which act as ligands of voltage-gated sodium channels in nerve axons [8, 9]. In... 

The relationship between the pharmacological effects elicited by menthol and ion channel dysfunction depends on the interaction of this monoterpene with distinct types of ion channels. In this way, the reported local anesthetic effects attributed to menthol and for some of its structural chemical homologues, such as thymol, carvacrol, and carveol, might be caused by a blockade of voltage-gated sodium channels [21, 25, 26]. On the other hand, a pronounced cytotoxic effect of menthol is correlated with the action of menthol in TRPM8 channels [22, 27]. At this point, we will make a short introduction to TRPM8 channels to further discuss the putative cytotoxic effects of menthol in various cell types. 

Ion channels are transmembrane proteins that span the cell membrane and are formed from one or more protein subunits. The channels are shaped like tunnels, which form pores through the plasma membrane. The pores have gates that open and close to allow ions to diffuse down their chemical gradient and move in or out of a cell. Ion channels are specific for certain types (and combinations of types) of ions, such as chloride, sodium, potassium, and calcium. 

Figure 4.10. Overview of nerve impulse transmission in chemical synapses. The action potential in the presynaptic nerve cell induces release of the nemotransmitter (e.g., acetylcholine) into the synaptic cleft. The transmitter binds to its receptor, e.g. the nicotinic acetylcholine receptor (NAR). The NAR is a hgand-gated channel it will open and become permeable to both and Na. This will move the membrane potential toward the average of the two respective equilibrium potentials however, in the process, the firing level of adjacent voltage-gated sodium charmels will be exceeded, and a full action potential will be triggered (inset).

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