Nicotinic acetylcholine receptors, or
nAChRs, are cholinergic receptors that form
ligand-gated ion channelLigand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...
s in the plasma membranes of certain neurons and on the postsynaptic side of the
neuromuscular junctionA neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract...
. As ionotropic receptors, nAChRs are directly linked to ion channels and do not use second messengers (as
metabotropic receptorMetabotropic receptor is a subtype of membrane receptors at the surface or in vesicles of eukaryotic cells.In the nervous system, based on their structural and functional characteristics, neurotransmitter receptors can be classified into two broad categories: metabotropic and ionotropic receptors...
s do).
Like the other type of
acetylcholine receptorAn acetylcholine receptor is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter.-Classification:...
– the
muscarinic acetylcholine receptorMuscarinic receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled in the plasma membranes of certain neurons and other cells...
(mAChR) – the nAChR is triggered by the binding of the
neurotransmitterNeurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
acetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
(ACh). However, whereas muscarinic receptors are also activated by
muscarineMuscarine, L--muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species, such as the deadly C. dealbata. Mushrooms in the genera Entoloma and Mycena have also been found to contain levels of muscarine which can be dangerous if ingested...
, nicotinic receptors can be opened by
nicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
- hence the name "nicotinic".
Nicotinic acetylcholine receptors are present in many tissues in the body and are the best-studied of the ionotropic receptors. The neuronal receptors are found in the
central nervous systemThe central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
and the
peripheral nervous systemThe peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
. The neuromuscular receptors are found in the
neuromuscular junctionA neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract...
s of
somatic muscleThe term somatic means 'of the body',, relating to the body. In medicine, somatic illness is bodily, not mental, illness. The term is often used in biology to refer to the cells of the body in contrast to the germ line cells which usually give rise to the gametes...
s; stimulation of these receptors causes
muscular contractionMuscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
.
Structure
Nicotinic receptors, with a molecular mass of 290 kDa, are made up of five subunits, arranged symmetrically around a central pore. They possess similarities with GABA
A receptors,
glycine receptorThe glycine receptor, or GlyR, is the receptor for the amino acid neurotransmitter glycine. GlyR is an ionotropic receptor that produces its effects through chloride current...
s, and the type 3 serotonin receptors (which are all ionotropic receptors), or the signature Cys-loop proteins.
In vertebrates, nicotinic receptors are broadly classified into two subtypes based on their primary sites of expression:
muscle-type nicotinic receptors and
neuronal-type nicotinic receptors. In the muscle-type receptors, found at the neuromuscular junction, receptors are either the embryonic form, composed of α1, β1, δ, and γ subunits in a 2:1:1:1 ratio, or the adult form composed of α1, β1, δ, and ε subunits in a 2:1:1:1 ratio. The neuronal subtypes are various homomeric or heteromeric combinations of twelve different nicotinic receptor subunits: α2 through α10 and β2 through β4. Examples of the neuronal subtypes include: (α4)
3(β2)
2, (α4)
2(β2)
3, and (α7)
5. In both muscle-type and neuronal-type receptors, the subunits are somewhat similar to one another, especially in the hydrophobic regions.
Binding the channel
As with all ligand-gated ion channels, opening of the nAChR channel pore requires the binding of a chemical messenger. Several different terms are used to refer to the molecules that bind receptors, such as
ligandIn biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...
. As well as the endogenous agonist
acetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
, agonists of the nAChR are
nicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
,
epibatidineEpibatidine is an alkaloid found on the skin of the endangered Ecuadorian frog, Epipedobates tricolor. These frogs, like other poison dart frogs, are best known for their ability to sequester poisons from their prey and secrete these poisons onto their backs. Many Amerindian tribes would swipe the...
, and
cholineCholine is a water-soluble essential nutrient. It is usually grouped within the B-complex vitamins. Choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation....
.
In neuronal nAChRs, the acetylcholine binding site is located at the α and either γ or δ subunits interface (or between two α subunits in the case of homomeric receptors) in the extracellular domain near the
N terminusThe N-terminus refers to the start of a protein or polypeptide terminated by an amino acid with a free amine group . The convention for writing peptide sequences is to put the N-terminus on the left and write the sequence from N- to C-terminus...
. When an agonist binds to the site, all present subunits undergo a conformational change and the channel is opened and a pore with a diameter of about 0.65 nm opens.
Opening the channel
Nicotinic AChRs may exist in different interconvertible conformational states. Binding of an agonist stabilises the open and desensitised states. Opening of the channel allows positively charged
ionAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s to move across it; in particular,
sodiumSodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
enters the cell and
potassiumPotassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
exits. The net flow of positively-charged ions is inward.
The nAChR is a non-selective cation channel, meaning that several different positively charged ions can cross through. It is permeable to Na
+ and K
+, with some subunit combinations that are also permeable to Ca
2+. The amount of sodium and potassium the channels allow through their pores (their conductance) varies from 50-110
pSThe siemens is the SI derived unit of electric conductance and electric admittance. Conductance and admittance are the reciprocals of resistance and impedance respectively, hence one siemens is equal to the reciprocal of one ohm, and is sometimes referred to as the mho. In English, the term...
, with the conductance depending on the specific subunit composition as well as the permeant ion.
It is interesting to note that, because some neuronal nAChRs are permeable to Ca
2+, they can affect the release of other neurotransmitters. The channel usually opens rapidly and tends to remain open until the
agonistAn agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...
diffusesMolecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
away, which usually takes about 1
millisecondA millisecond is a thousandth of a second.10 milliseconds are called a centisecond....
. However, AChRs can sometimes open with only one agonist bound and, in rare cases, with no agonist bound, and they can close spontaneously even when ACh is bound. Therefore, ACh binding creates only a probability of pore opening, which increases as more ACh binds.
Effects
The activation of receptors by nicotine modifies the state of neurons through two main mechanisms. On one hand, the movement of cations causes a
depolarizationIn biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
of the plasma membrane (which results in an
excitatory postsynaptic potentialIn neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
in
neuronA neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s), but also by the activation of
voltage-gated ion channelVoltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells....
s. On the other hand, the entry of calcium acts, either directly or indirectly, on different
intracellular cascadesA biochemical cascade is a series of chemical reactions in which the products of one reaction are consumed in the next reaction. There are several important biochemical cascade reactions in biochemistry, including the enzymatic cascades, such as the coagulation cascade and the complement system,...
leading, for example, to the regulation of the activity of some
geneA gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s or the release of neurotransmitters.
Receptor desensitisation
Ligand-bound desensitisation of receptors was first characterised by Katz and Thesleff in the nicotinic acetylcholine receptor.
Prolonged or repeat exposure to a stimulus often results in decreased responsiveness of that receptor toward a stimulus, termed desensitisation (for example:
myasthenia gravisMyasthenia gravis is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability...
). nAChR function can be modulated by phosphorylation by the activation of second messenger-dependent protein kinases. PKA and
PKCProtein kinase C also known as PKC is a family of enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in...
have been shown to phosphorylate the nAChR resulting in its desensitisation. It has been reported that, after prolonged receptor exposure to the agonist, the agonist itself causes an agonist-induced conformational change in the receptor, resulting in receptor desensitisation. This receptor desensitisation has been previously modeled in the context of a two-state mathematical model (see this link
http://www.bio-balance.com/Graphics.htm)
Desensitised receptors can revert back to a prolonged open state when an agonist is bound in the presence of a positive allosteric modulator, for example PNU-120596.
Roles
The subunits of the nicotinic receptors belong to a multigene family (16 members in humans) and the assembly of combinations of subunits results in a large number of different receptors (for more information see the
Ligand-Gated Ion Channel database). These receptors, with highly variable
kineticThe kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
,
electrophysiologicalElectrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
and
pharmacologicalPharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...
properties, respond differently to
nicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
, at very different effective concentrations. This functional diversity allows them to take part in two major types of neurotransmission. Classical synaptic transmission (wiring transmission) involves the release of high concentrations of neurotransmitter, acting on immediately neighboring receptors. In contrast, paracrine transmission (volume transmission) involves neurotransmitters released by synaptic buttons, which then diffuse through the extra-cellular medium until they reach their receptors, which may be distant. Nicotinic receptors can also be found in different synaptic locations; for example the muscle nicotinic receptor always functions post-synaptically. The neuronal forms of the receptor can be found both post-synaptically (involved in classical neurotransmission) and pre-synaptically where they can influence the release of multiple neurotransmitters.
Subunits
To date, 17 nAChR subunits have been identified, which are divided into muscle-type and neuronal-type subunits. Of these 17 subunits, α2-α7, and β2-β4 have been cloned in humans, the remaining genes identified in chick and rat genomes.
The nAChR subunits have been divided into 4 subfamilies (I-IV) based on similarities in protein sequence. In addition, subfamily III has been further divided into 3 tribes.
| Neuronal-type |
Muscle-type |
| I |
II |
III |
IV |
| α9 Neuronal acetylcholine receptor subunit alpha-9 is a protein that in humans is encoded by the CHRNA9 gene.Selective block of α9α10 nicotinic acetylcholine receptors by the conotoxin RgIA has been shown to be analgesic in an animal model of nerve injury pain....
, α10Neuronal acetylcholine receptor subunit alpha-10 also known as cholinergic receptor nicotinic alpha 10 is a protein that in humans is encoded by the CHRNA10 gene...
|
α7 Neuronal acetylcholine receptor subunit alpha-7 is a protein that in humans is encoded by the CHRNA7 gene.-See also:* Alpha-7 nicotinic receptor* Nicotinic acetylcholine receptor* Acetylcholine receptor...
, α8 |
1 |
2 |
3 |
α1 Acetylcholine receptor subunit alpha is a protein that in humans is encoded by the CHRNA1 gene.-Interactions:Cholinergic receptor, nicotinic, alpha 1 has been shown to interact with CHRND....
, β1Acetylcholine receptor subunit beta is a protein that in humans is encoded by the CHRNB1 gene....
, δAcetylcholine receptor subunit delta is a protein that in humans is encoded by the CHRND gene.-Interactions:CHRND has been shown to interact with Cholinergic receptor, nicotinic, alpha 1....
, γAcetylcholine receptor subunit gamma is a protein that in humans is encoded by the CHRNG gene.-Further reading:...
, εAcetylcholine receptor subunit epsilon is a protein that in humans is encoded by the CHRNE gene....
|
| α2 Neuronal acetylcholine receptor subunit alpha-2 is a protein that in humans is encoded by the CHRNA2 gene....
, α3Neuronal acetylcholine receptor subunit alpha-3 is a protein that in humans is encoded by the CHRNA3 gene.- Interactive pathway map :...
, α4Neuronal acetylcholine receptor subunit alpha-4 is a protein that in humans is encoded by the CHRNA4 gene....
, α6Cholinergic receptor, nicotinic, alpha 6, also known as CHRNA6, is a human gene, which codes for the α6 subunit found in certain types of nicotinic acetylcholine receptors found primarily in the brain...
|
β2 Neuronal acetylcholine receptor subunit beta-2 is a protein that in humans is encoded by the CHRNB2 gene....
, β4Neuronal acetylcholine receptor subunit beta-4 is a protein that in humans is encoded by the CHRNB4 gene....
|
β3 Neuronal acetylcholine receptor subunit beta-3 is a protein that in humans is encoded by the CHRNB3 gene....
, α5Neuronal acetylcholine receptor subunit alpha-5 is a protein that in humans is encoded by the CHRNA5 gene.- Function :Nicotinic acetylcholine receptors , such as CHRNA5, are members of a superfamily of ligand-gated ion channels that mediate fast signal transmission at synapses. The nAChRs are...
|
- Alpha genes: (muscle), (neuronal), , , , , , , ,
- Beta genes: (muscle), (neuronal), , ,
- Other genes: (delta), (epsilon), (gamma)
Notable variations
Nicotinic receptors are pentamers of these subunits; i.e., each receptor contains five subunits. Thus, there is an immense potential of variation of the aforementioned subunits. However, some of them are more notable than others, to be specific, (α1)
2β1δε (muscle-type), (α3)
2(β4)
3 (ganglion-type), (α4)
2(β2)
3 (CNS-type) and (α7)
5 (another CNS-type). A comparison follows:
| Receptor-type | Location | Effect | Nicotinic agonists | Nicotinic antagonist A nicotinic antagonist is a type of anticholinergic that inhibits the action at nicotinic acetylcholine receptors. These compounds are mainly used for peripheral muscle paralysis in surgery, but some centrally acting compounds such as bupropion, mecamylamine, and 18-methoxycoronaridine block...
s |
| Muscle-type The muscle-type nicotinic receptor is a type of nicotinic acetylcholine receptor, consisting of the subunit combination 2β1δε or 2β1δγ....
:
(α1)2β1δε
or
(α1)2β1δγ |
Neuromuscular junction A neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract...
|
EPSP In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
, mainly by increased Na+Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and K+Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
permeability |
- acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
- carbachol
Carbachol , also known as carbamylcholine, is a drug that binds and activates the acetylcholine receptor. Thus it is classified as a cholinergic agonist. It is primarily used for various ophthalmic purposes, such as for treating glaucoma, or for use during ophthalmic surgery...
- suxamethonium
|
α-bungarotoxin
α-conotoxin
tubocurarineTubocurarine is a neuromuscular-blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in anesthesia to provide skeletal muscle relaxation during surgery or mechanical ventilation...
pancuroniumPancuronium is a muscle relaxant with various purposes. It is the second of three drugs administered during most lethal injections in the United States.- Mode of action :...
atracuriumAtracurium besylate is a neuromuscular-blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in anesthesia to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical...
* |
| Ganglion-type The ganglion type nicotinic receptor is a type of nicotinic acetylcholine receptor, consisting of the subunit combination 23.It is located in the autonomic ganglia, where activation yields EPSP, mainly by increased Na+ and K+ permeability....
:
(α3)2(β4)3 |
autonomic ganglia |
EPSP In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
, mainly by increased Na+Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and K+Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
permeability |
acetylcholine The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
carbacholCarbachol , also known as carbamylcholine, is a drug that binds and activates the acetylcholine receptor. Thus it is classified as a cholinergic agonist. It is primarily used for various ophthalmic purposes, such as for treating glaucoma, or for use during ophthalmic surgery...
nicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
epibatidineEpibatidine is an alkaloid found on the skin of the endangered Ecuadorian frog, Epipedobates tricolor. These frogs, like other poison dart frogs, are best known for their ability to sequester poisons from their prey and secrete these poisons onto their backs. Many Amerindian tribes would swipe the...
dimethylphenylpiperaziniumDimethylphenylpiperazinium is a nicotinic acetylcholine receptor agonist which is selective for the ganglionic subtype....
|
mecamylamineMecamylamine is a nonselective and noncompetitive antagonist of the nicotinic acetylcholine receptors that was introduced in the 1950s as an antihypertensive agent.- Uses :...
trimetaphan
hexamethoniumHexamethonium is a ganglionic blocker, a nicotinic nACh receptor antagonist that acts in autonomic ganglia by binding mostly in or on the NN receptor, and not the acetylcholine binding site itself...
bupropionBupropion is an atypical antidepressant and smoking cessation aid. The drug is a non-tricyclic antidepressant and differs from most commonly prescribed antidepressants such as SSRIs, as its primary pharmacological action is thought to be norepinephrine-dopamine reuptake inhibition...
dextromethorphanDextromethorphan is an antitussive drug. It is one of the active ingredients in many over-the-counter cold and cough medicines, such as Robitussin, NyQuil, Dimetapp, Vicks, Coricidin, Delsym, and others, including generic labels. Dextromethorphan has also found other uses in medicine, ranging...
ibogaineIbogaine is a naturally occurring psychoactive substance found in a number of plants, principally in a member of the Apocynaceae family known as Iboga . A hallucinogen with both psychedelic and dissociative properties, the substance is banned in some countries; in other countries it is being used...
18-methoxycoronaridine-18-Methoxycoronaridine is a derivative of ibogaine invented in 1996 by the research team around the pharmacologist Stanley D. Glick from the Albany Medical College and the chemist Martin E. Kuehne from the University of Vermont...
|
Heteromeric CNS-type:
(α4)2(β2)3The alpha-4 beta-2 nicotinic receptor, also known as the α4β2 receptor, is a type of nicotinic acetylcholine receptor, consisting of α4 and β2 subunits...
|
BrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
|
Post- In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
and presynaptic excitation, mainly by increased Na+Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and K+Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
permeability |
nicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
epibatidineEpibatidine is an alkaloid found on the skin of the endangered Ecuadorian frog, Epipedobates tricolor. These frogs, like other poison dart frogs, are best known for their ability to sequester poisons from their prey and secrete these poisons onto their backs. Many Amerindian tribes would swipe the...
acetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
cytisineCytisine, also known as baphitoxine and sophorine, is a pyridine-like alkaloid. In medical use, it improves the rate of smoking cessation. It is less effective but much cheaper than similar products. Its structure is similar to nicotine and has similar pharmacological effects...
varenicline |
mecamylamineMecamylamine is a nonselective and noncompetitive antagonist of the nicotinic acetylcholine receptors that was introduced in the 1950s as an antihypertensive agent.- Uses :...
methylcaconitine
α-conotoxin |
Further CNS-type:
(α3)2(β4)3The alpha-3 beta-4 nicotinic receptor, also known as the α3β4 receptor, is a type of nicotinic acetylcholine receptor, consisting of α3 and β4 subunits. It is located in the brain, where activation yields post- and presynaptic excitation....
|
BrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
|
Post- In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
and presynaptic excitation |
nicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
epibatidineEpibatidine is an alkaloid found on the skin of the endangered Ecuadorian frog, Epipedobates tricolor. These frogs, like other poison dart frogs, are best known for their ability to sequester poisons from their prey and secrete these poisons onto their backs. Many Amerindian tribes would swipe the...
acetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
cytisineCytisine, also known as baphitoxine and sophorine, is a pyridine-like alkaloid. In medical use, it improves the rate of smoking cessation. It is less effective but much cheaper than similar products. Its structure is similar to nicotine and has similar pharmacological effects...
|
hexamethoniumHexamethonium is a ganglionic blocker, a nicotinic nACh receptor antagonist that acts in autonomic ganglia by binding mostly in or on the NN receptor, and not the acetylcholine binding site itself...
mecamylamineMecamylamine is a nonselective and noncompetitive antagonist of the nicotinic acetylcholine receptors that was introduced in the 1950s as an antihypertensive agent.- Uses :...
tubocurarineTubocurarine is a neuromuscular-blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in anesthesia to provide skeletal muscle relaxation during surgery or mechanical ventilation...
|
Homomeric CNS-type:
(α7)5The alpha-7 nicotinic receptor, also known as the α7 receptor, is a type of nicotinic acetylcholine receptor, consisting entirely of α7 subunits....
|
BrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
|
Post- In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
and presynaptic excitation, mainly by increased Ca2+Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
permeability |
epibatidineEpibatidine is an alkaloid found on the skin of the endangered Ecuadorian frog, Epipedobates tricolor. These frogs, like other poison dart frogs, are best known for their ability to sequester poisons from their prey and secrete these poisons onto their backs. Many Amerindian tribes would swipe the...
dimethylphenylpiperaziniumDimethylphenylpiperazinium is a nicotinic acetylcholine receptor agonist which is selective for the ganglionic subtype....
|
mecamylamineMecamylamine is a nonselective and noncompetitive antagonist of the nicotinic acetylcholine receptors that was introduced in the 1950s as an antihypertensive agent.- Uses :...
memantine
α-bungarotoxin |
External links