Acetylcholine is a neurotransmitter. Acetylcholine: features, preparations, properties

передатчик нервного возбуждения в ЦНС, окончаниях парасимпатических нервов и вегетативных ганглиях. Acetylcholine is a transmitter of nervous excitation in the central nervous system, endings of parasympathetic nerves and vegetative ganglia. He performs the most important tasks in the processes of life. Analogous functions include amino acids, histamine, dopamine, serotonin, adrenaline. Acetylcholine is considered one of the most important transmitters of impulses in the brain. Consider this substance in more detail.

General information

The endings of the fibers, from which the mediator acetylcholine transfers, are called cholinergic. In addition, there are special elements with which it interacts. They are called holinoretseptorami. These elements are complex protein molecules - nucleoproteins. отличаются тетрамерной структурой. Acetylcholine receptors differ in tetrameric structure. They are localized on the outer surface of the plasma (postsynaptic) membrane. These molecules are inherently heterogeneous in nature.

In experimental studies and for medical purposes, the drug "Acetylcholine chloride" is used, presented in a solution for injections. Other drugs based on this substance are not produced. There are synonyms for the drug: "Myohol", "Acekolin", "Cytacholine".

Classification of choline proteins

Some molecules are located in the region of cholinergic postganglionic nerves. It is a region of smooth muscles, hearts, glands. They are called m-cholinergic receptors - muscarinic-sensitive. Other proteins are located in the region of the ganglionic synapses and in the neuromuscular somatic structures. They are called n-holinoretseptorami - nicotine sensitive.

Explanations

The above classification is due to the specificity of the reactions that arise when these biochemical systems and acetylcholine interact . , в свою очередь, объясняет причины некоторых процессов. This , in turn, explains the reasons for some processes. For example, pressure reduction, increased secretion of gastric, salivary and other glands, bradycardia, narrowing of the pupils, etc., when affecting muscarinic-sensitive proteins and reducing skeletal muscles, etc., when exposed to nicotine-sensitive molecules. At the same time recently, scientists have begun to divide m-holinoretseptory into subgroups. The role and localization of m1 and m2 molecules has been most studied today.

Specificity of influence

не избирательный элемент системы. Acetylcholine is not an elective element of the system. In one degree or another, it affects both m- and n-molecules. Interest is the muscarin-like effect that acetylcholine exerts . воздействие проявляется в замедлении сердечного ритма, расширении кровеносных сосудов (периферических), активизации перистальтики кишечника и желудка, сокращении мышц матки, бронхов, мочевого, желчного пузыря, интенсификации секреции бронхиальных, потовых, пищеварительных желез, миозе. This effect is manifested in the slowing of the heart rhythm, the expansion of blood vessels (peripheral), the activation of peristalsis of the intestine and stomach, the contraction of the uterus, bronchi, urinary, gall bladder, the intensification of secretion of bronchial, sweat, digestive glands, miosis.

Narrowing of the pupil

The circular muscle of the iris, innervated by postganglionic fibers in the oculomotor nerve, begins to shrink at the same time as the ciliary nerve . In this case, there is a relaxation of the zinn ligament. As a result, there is a spasm of accommodation. The constriction of the pupil, associated with the influence of acetylcholine, is usually accompanied by a decrease in intraocular pressure. This effect is partly due to the expansion of the membrane in the helmet canal and the fountain spaces against the background of miosis and flattening of the iris. This helps to improve the outflow of fluid from the internal eye environments.

на основе других подобных ему веществ используются при лечении глаукомы. Due to the ability to lower intraocular pressure, like acetylcholine, preparations based on other similar substances are used in the treatment of glaucoma. Among them, in particular, include anticholinesterase drugs, holinomimetiki.

Nicotin-sensitive proteins

обуславливается его участием в процессе передачи сигналов с преганглионарных нервных волокон на постганглионарные, находящиеся в вегетативных узлах, и с двигательных окончаний на поперечнополосатые мышцы. The nicotine-like effect of acetylcholine is due to its participation in the process of signal transmission from preganglionic nerve fibers to postganglionic ones located in vegetative nodes and from motor endings to striated muscles. In small doses, the substance acts as a physiological transmitter of excitation. , то может развиться стойкая деполяризация в районе синапсов. If acetylcholine is elevated , then persistent depolarization in the synapse region can develop. There is also the possibility of blocking the transmission of excitation.

CNS

играет роль передатчика сигналов в различных мозговых отделах. Acetylcholine in the body plays the role of a signal transmitter in various brain departments. In a small concentration, it can facilitate, and in a large concentration - slow down the synaptic translation of impulses. Changes in the metabolism of substances can contribute to the development of brain disorders. психотропной группы. Antagonists, which are contrasted with acetylcholine, are drugs of the psychotropic group. With their overdose, there may be a violation of higher nervous functions (hallucinogenic effect, etc.).

Synthesis of acetylcholine

It occurs in the cytoplasm in the nerve endings. Stocks of matter are located in presynaptic terminals in the form of bubbles. The onset of the action potential results in the release of acetylcholine from several hundred "capsules" into the synaptic cleft. The substance released from the vesicles binds to the postsynaptic membrane with specific molecules. This increases its permeability for sodium, calcium and potassium ions. As a result, there is an exciting postsynaptic potential. The effect of acetylcholine is limited by its hydrolysis with the participation of the enzyme acetylchol esterase.

Physiology of nicotinic molecules

The first description was promoted by intracellular tapping of electrical potentials. The nicotinic receptor was one of the first to record currents passed through a single channel. In the open state, ions K + and Na +, less divalent cations can pass through it. The conductivity of the channel is expressed in a constant value. The duration of the open state, however, is a characteristic that depends on the potential voltage applied to the receptor. At the same time, the latter is stabilized during the transition from membrane depolarization to hyperpolarization. In addition, there is a phenomenon of desensetization. It occurs with prolonged use of acetylcholine and other antagonists, which reduces the sensitivity of the receptor and increases the duration of the open state of the canal.

Electrical Irritation

Dihydro-β-erythroidin blocks the nicotinic receptors of the brain and nerve ganglia when they manifest a cholinergic response. They are also characterized by high affinity affinity with tritium-labeled nicotine. Sensitive neuronal receptors of αBGT in the hippocampus are characterized by a low susceptibility of acetylcholine, in contrast to insensitive αBGT elements. The first selective competitive antagonist is methylikaconitin.

Individual anabeese derivatives produce a selective activation effect on the αBGT receptor group. The conductivity of their ion channel is quite high. These receptors are distinguished by unique volt-dependent characteristics. Cellular current with the participation of depolarization values of e. Potential indicates a decrease in the passage of ions through the channels.

This phenomenon is regulated by the content of Mg2 + elements in the solution. This group differs from the receptors of muscle cells. The latter do not undergo any changes in the ion current when the values of the membrane potential are adjusted . Moreover, a N-methyl-D-aspartate receptor, which has a relative permeability for Ca2 + elements, shows the opposite picture. When the potential is increased to hyperpolarizing values and the content of Mg2 + ions increases, the ion current is blocked.

Features of muscarinic molecules

M-holinoretseptory belong to the class of serpentine. They transmit pulses through heterotrimeric G-proteins. A group of muscarinic receptors was identified because of their ability to bind the alkaloid muscarin. Indirectly, these molecules were described in the early 20th century when studying the effects of curare. A direct study of this group began in the 20-30's. The same century after the identification of the acetylcholine compound as a neurotransmitter supplying the impulse to the neuromuscular synapses. M-proteins are activated by the influence of muscarin and are blocked by atropine, n-molecules are activated by the action of nicotine and are blocked by curare.

After a time, a large number of subtypes were revealed in both groups of receptors. In the neuromuscular synapses there are only nicotinic molecules. Muscarinic receptors are found in glandular and muscular cells, as well as - together with n-cholinergic receptors - in neurons of the central nervous system and nervous ganglia.

Functions

Muscarinic receptors have a whole complex of different properties. First of all, they are located in the autonomous ganglia and the postganglionic fibers that leave them, directed towards the target organs. This indicates the involvement of the receptors in the translation and modulation of parasympathetic effects. These include, for example, contraction of smooth muscles, vasodilatation, increased secretion of glands, a decrease in the frequency of heart contractions. The cholinergic fibers of the central nervous system, which contain interneurons and muscarinic synapses, are concentrated mainly in the cerebral cortex, the hippocampus, the stem nuclei, and the striatum. In other areas, they are found in smaller quantities. Central m-holinoretseptory affect the regulation of sleep, memory, training, attention.