Distant interactions. Sex cells and fertilization Intercellular interactions, contact and distant

Numerous experiments indicate that some component of SCI is not a metabolic by-product, but can play a functional role and is the basis for some non-chemical interactions of biosystems. This was evidenced by the well-known experiments of A.G. Gurvich with onion roots [Gurvich, 1945] and his other works on mitogenetic radiation.

The phenomenon of distant, i.e. without direct contact and non-chemically mediated, intercellular interactions (CMI) was strictly established and studied by V.P. Kaznacheev and his colleagues in experiments with a “mirror” cytopathic effect [Kaznacheev et al., 1979, 1980; Kaznacheev and Mikhailova, 1981, 1985]. Cells under the influence of extreme factors of a physical, chemical or biological nature caused morphological changes in the recipient cell culture (placed in an isolated chamber adjacent to the first and not exposed to these factors) similar to changes in the first inducer cell culture (with a reliable probability value of 70 -78%). The interaction of cell cultures was carried out only through ultra-weak electromagnetic radiation from the cells themselves through a quartz (or mica) plate, transparent in the ultraviolet and infrared ranges. In these experiments, for the first time, it was possible to completely eliminate the chemical component of DMV. UHFs were also studied in a model that allows us to consider the role of electromagnetic radiation in the life cycle of a cell, in contrast to the model of extreme effects on the cellular system. As cultures spread apart or as quartz and mica substrates thicken, the efficiency of communication decreases, which means that the effectiveness of the mirror cytopathic effect depends on the absorption and scattering of electromagnetic waves - information carriers. Let us note the following properties of the mirror effect [Ibid]: 1. The mirror cytopathic effect is maximally manifested in pairs of homologous cell cultures, weaker in closely related cells; in heterogeneous, genetically distant from each other, there is no mirror cytopathic effect. 2. Healthy cells that have received the information from the affected cell cultures, being in contact with the next new healthy culture, are able to transmit it further; the mirror effect has the ability to pass with gradual fading up to 3-4 passages. 3. The manifestation of the effect depends on geographic latitude, solar activity and geomagnetic conditions.

One of the possible general approaches to posing and studying questions of this kind was put forward by V.P. Treasurer. According to the concept of V.P. Kaznacheev [Ibid], a biosystem (cell) can be represented as a nonequilibrium photon constellation that exists due to the influx of energy from the outside. The purely chemical mechanism of intercellular and intracellular communication may not be primary, but a consequence of more complex processes. A functioning cell is the source and carrier of a complex electromagnetic field, the structure of which is generated by biochemical processes, and controls all metabolic activities of the cell. (Membranes can be considered as the main structure - the carrier of a nonequilibrium photon constellation.) Photon constellations can be considered as the primary substrate of life itself, not as a manifestation of a secondary method of transmitting biological information. This constellation has a high degree of reliability and is the information-regulating system of the cell. Presumably, in the macromolecular protein-nucleic acid form of living matter (cells) there are other - quantum field - forms of living matter that have the ability to move in the optical medium to other unaffected macromolecular protein-nucleic acid organizations, change their state and move again, while from from one cell culture to another there is a flow of the intended form of living matter. Thus, the essence of living matter is field. This means that the material flow in the existing electromagnetic earthly environment in its movement, entering the space populated by atoms and molecules, under appropriate physical and chemical conditions, builds a secondary complex macromolecular structure from them. These structures can migrate, under appropriate conditions, from one macromolecular structure (cells, living organisms) to another, interact with each other, and change secondary biochemical properties.

Note that this concept is confirmed by the results of experiments by L. Montaigner (section 2.2).

Distant interactions mediated by SSI in the range from ultraviolet to near-infrared affect the activity of enzymes [Baskakov and Voeikov, 1996], the activity and morphology of cells and tissues [Kaznacheev and Mikhailova, 1985], the life cycle of the cell [Ibid], regulate locomotion and mutual orientation of cells determines the rate of development of embryos and their morphological features [Burlakov et al., 1999a, 1999b], and participates in the interaction of neutrophils and whole blood samples. Distant interactions (DI) are not limited to the unilateral action of one biological system on another, but also include bilateral interaction of two chemically isolated biological systems [Ibid], as well as “self-interaction” [Burkov et al., 2008]. DVs were found between the cells of not only eukaryotes, but also bacteria [Nikolaev, 1992]. DV take place at the organismal level, at the population level [Burlakov et al., 1999; Volodyaev and Beloussov, 2007] and, possibly, ecosystems.

It should be noted that DVs are quite weak, depend on many factors, and in some cases difficulties arise in controlling experimental conditions and reproducibility of their results. Nevertheless, radiation for the biosystem itself can serve as its internal information transmission system, an “attribute of life” [Kaznacheev and Mikhailova, 1985]. From this point of view, the study of DV is important for understanding the coordination of intracellular molecular processes, control of protein activity and coordination of genetic and biochemical systems that maintain homeostasis.

The question of the functional role of SSI is still debatable, but in any case it has been established that SSI reflects the biological state of organisms and their population interactions.

The mechanisms that ensure cell connection and intercellular information exchange were formed during the evolutionary transition from a single-celled organism to a multicellular one. Intercellular interactions are necessary to coordinate the activity, differentiation, motility and growth of cells within tissues and organs. The cells that make up the tissue are in contact not only with each other, but also with the extracellular matrix, consisting of fibers, protein, collagen and gelatin-like substances, represented by glycoproteins and proteoglycans. The extracellular matrix holds cells together and provides physical support and an environment in which they move and interact. Physiology and fundamentals of anatomy: textbook / Ed. A.V. Kotova, T.N. Loseva. 2011. - 1056 p. (Series " Educational literature for medical students")

Along with the renewal of the cell population, renewal of intracellular structures is constantly observed in the cells themselves (intracellular physiological regeneration).

Cell growth manifests itself in changes in their size and shape. Cell growth is not unlimited and is determined by the optimal nuclear-cytoplasmic ratio.

Cell movements. Cell migration is most typical during the gastrulation period. Migration is carried out using several mechanisms. So, they distinguish chemotaxis- movement of cells in the direction of the concentration gradient of a chemical agent. Haptotaxis- mechanism of cell movement along a concentration gradient of an adhesion molecule. Contact orientation- when in any obstacle there is only one channel left for movement. Contact inhibition- this method of movement is observed in the tapholes of a smooth ridge.

Migration is purposeful, the cells do not move chaotically, but along certain paths precisely to those parts of the embryo where mature derivatives will subsequently be formed from them. Disturbances in cell migration that occur during embryogenesis lead to the formation of such birth defects development, such as heterotopia and ectopia, i.e. to abnormal localization of organs or structures.

Mechanisms of intercellular interaction. The formation and functioning of all tissue structures can occur only on the basis of their mutual recognition and mutual adhesion, i.e. the ability of cells to selectively attach to each other or to components of the extracellular matrix. Cell adhesion is realized by special glycoproteins - adhesion molecules - cadherin, laminin, connexin, etc. Physiology and fundamentals of anatomy: textbook / Ed. A.V. Kotova, T.N. Loseva. 2011. - 1056 p. (Series "Educational literature for medical students")

Mechanisms of interaction between cells and substrate. They include the formation of cell receptors for extracellular matrix molecules. The latter include cell derivatives. Among which, the most studied adhesion molecules are collagen, fibronectin, laminin, tenascin, etc.

To communicate between migrating cells and the extracellular matrix, cells form specific receptors. These include, for example, syndecan, which ensures contact of the epithelial cell with the basement membrane due to adhesion to fibronectin and collagen molecules.

Distant intercellular interactions carried out through the secretion of hormones and growth factors. The latter are substances that have a stimulating effect on the proliferation and differentiation of cells and tissues.

The influence of the position of blastomeres on their differentiation. The differentiation of a cell is influenced by its position in a certain place in the embryo at a certain time. The outer cells form the trophoblast, and the inner cells form the embryo. Experience with blastomere transplantation shows that the formation of trophoblast or embryonic cells from blastomeres is determined by where the cell ends up - on the surface or inside a group of cells.

Gastrulation begins at the end of the second week of development and is characterized by the appearance of the ability of cells to move. With the onset of gastrulation, the first tissue-specific genes are activated. The embryoblast is divided into epiblast ( layer of cylindrical cells) and hypoblast ( layer of cubic cells facing the blastocoel). The epiblast and hypoblast together form a two-layer germinal disc ( blastodisc). Subsequently, in place of the two-layer germinal disc, the primary germ layers develop through migration and proliferation of cells: ectoderm, mesoderm and endoderm.

Hypoblast. The formation of the hypoblast (primary endoderm) occurs along a caudal-cranial gradient. The cells of the ventral part of the inner cell mass facing the blastocoel are separated into a thin layer - the hypoblast. Hypoblast cells are evicted from the inner cell mass due to weak adhesive interaction between them. Intensely proliferating hypoblast cells move along the inner surface of the trophoblast and form the extraembryonic endoderm of the yolk sac wall adjacent to the trophoblast. Histology, embryology, cytology: textbook for universities / Edited by E.G. Ulumbekova, Yu.A. Chelysheva - 3rd ed., - M.: GEOTAR-Media, 2012.

Lecture on the course “Cytology”.
Author-compiler: Associate Professor of the Department of Anatomy,
Physiology of Humans and Animals FSBEI HPE "ChSPU",
Doctor of Biological Sciences Efimova N.V.
Chelyabinsk, 2012.

Lecture outline:

LECTURE PLAN:
1) Contact interactions of cells.
2) Distant cell interactions.

Question 1: Contact interactions of cells.

The role of intercellular contacts in a multicellular organism:

Existence
individual
liquid
compartmentmen
(medium) with different
molecular
composition
is an important
for development and
maintaining
multicellular
organisms.
Compartments in a multicellular organism are separated by
epithelial cell layers (layers) that function
as barriers to maintaining a certain internal environment
(homeostasis) in each individual organ and the body as a whole.

Intercellular contacts are...

... specialized cells
structures that hold cells together
formation of tissues that create barriers
permeability and serving for
intercellular communication.

Functional types of MCC:

ICC
1. Closing
(dense)
contacts
2. Adhesive
(attachment)
contacts
3. Communication
(conductive)
contacts

external environment
internal environment
form in layer
cell barrier
permeability,
separating
different in
chemical composition
environment (for example
external and
internal environment) and
obstructive
penetration
substances through
intercellular
space.
zonula occludens = zonule of closure

Examples of normally open contacts:

morula and trophoblast (emryogenesis),
alveolocytes of the lungs,
vascular endothelium,
intestinal and kidney epithelium

I. Normally closed (solid) contacts:

0.6 µm
located on
apical
surfaces
cells;
consist of
continuous
protein chains
molecules (claudins
and occludins),
connecting
(“stitching”)
membranes of neighboring
cells.

10. Normally closed (solid) contacts

11. Functions of tight junctions:

1) Mechanically connect epithelial cells between
itself → epithelial layer.
2) Provide a permeability barrier
paracellular (intercellular) pathway
transport of most substances through
epithelium, i.e. substances selectively
transported only through membranes and
cytoplasm of cells.
3) Functional polarity of cells is maintained
epithelium. On the apical (looking into the lumen
organ or on the surface of the body) surface
only proteins are localized, and on the basolateral
(lower-lateral) - other proteins.

12. The number of Tight Junctions correlates with epithelial permeability.

Epithelia with
small
number of PCs
(renal
tubules
nephron) more
permeable
for water and
solutions than
epitheliis
numerous PCs
(uric
bubble).

13. Tight contacts:

To maintain the integrity of tight junctions
divalent cations Mg2+ and Ca2+ are required.
Contacts can be dynamically rebuilt
(due to changes in expression and degree
polymerization of occludin) and temporarily
open (for example, for the migration of leukocytes
through intercellular spaces).

14. Trans-endothelial cell migration: norm and pathology...

Staphylococcus aureus does
tunnel in the endothelium of capillaries.

15.II. Adhesive (attachment) contacts

Mechanically fastened
cells between each other
with intercellular matrix
or basal plate.
Formed between cells
those fabrics that can
be subject to friction
stretching and others
mechanical stress
(for example, epithelial
cells, heart cells
muscles).
0.1 mm

16. 2.1. Desmosome is the most common and complexly organized ICC:

From the cytoplasm to
desmosomes
are attached
1 intermediate
filaments
(keratin or
desminaceae) which
form in the cytoplasm
network with
great strength for
gap
Through desmosomes
intermediate
neighboring filaments
cells combine into
continuous network
covering the entire fabric.

17. Ultrastructure of the desmosome:

2
Desmosome in the perimembrane
space presented
attachment plate consisting
of 12 types of adapter proteins
(desmoplakin), which are connected
with intermediate filaments.
3 Cell adhesion proteins,
Desmosome = spot of adhesion
(macula adherens)
desmosome-forming cadherins are
transmembrane Ca2+ binding proteins;
provide homophilous
connection of cells when between
two identical ones join together
according to the structure of the protein molecule.

18. DESMOSOMA

1) intermediate filaments
cytoskeleton
(keratins,
desmins);
2) adapter
squirrels
(desmoplakins);
3) adhesive
transmembrane
proteins (cadherins).

19. Types of desmosomes:

In violation
functions of desmosomes
associated skin
diseases that
united under
name
"pemphigus"
(pemphigus).
There are 3 types of desmosomes: punctate, encircling and
hemidesmosomes (hemidesmosomes).
Punctate desmosome
represents a small
platform (diameter up to 0.5
µm) connecting the membranes
two neighboring cells. Quantity
punctate desmosomes on one
cell can reach 2,000.
Hemidesmosomes - contacts,
formed between cells and
extracellular matrix.

20. Skin diseases are associated with dysfunction of desmosomes, which are collectively called “pemphigus” (pemphigus).

They are usually autoimmune in nature, although
similar pathologies can also be hereditary.
In pemphigus, antibodies attack the desmosome proteins desmogleins. Patients develop blisters because the layers
the epidermis ruptures, some of its cells die, and in
The resulting cavities receive intercellular fluid.
In case of dysfunction of hemidesmosomes (hemidesmosomes)
epidermolysis bullosa develops (congenital, bullous
pemphigus). At the slightest mechanical impact
the epidermis of the skin lags behind the basal lamina, underneath
blisters form with serous or hemorrhagic
content. One of the causes of this disease is mutations
collagen XVII gene. This variant of the disease
inherited in an autosomal recessive manner.

21. Symptoms of pemphigus:

Blisters with serous or
hemorrhagic contents

22. 2.2. Adhesion Belt:

1
2
Zonula adherens =
adhesion belt
Entirely surrounds the cell and
ensures adhesion
(adhesion) of neighboring cells.
From the cytoplasmic side
formed by electron-dense plates,
consisting of actin
filaments “sewn” to
plasmalemma
auxiliary
adapter proteins (αactinin, vinculin, catenin).
In the intermembrane
space of the ICC is determined
interaction
transmembrane proteins -
3 cadherins.

23. 2.3. Focal cell contacts

Matrix receptor proteins bind fibers
matrix with membrane receptors, which in their
turn through linker (adapter) proteins connect
with actin filaments of the cytoskeleton, which
may strain the contact.

24. FC signaling function

Induction
reproduction
actin
In focal contacts
also contained
special regulatory
proteins (kinases - K), which
can change state and
contact strength.
Induction
pseudopodium
The red dotted line indicates hypothetical paths
conducting signals from focal contacts into the cell.
Through a series of intermediate proteins (red circles), such
pathways can activate cell proliferation and cause
formation of new pseudopodia on the cell surface.

25. MCC and cell behavior

Proliferation
cells

26. MCC and cell behavior...

Assembly and disassembly of focal
contacts (FC) occurs in 10120 min, and these structures are typical for
relatively slow moving
cells.

27. Focal contacts are a necessary condition for cell migration...

Breast cancer cell migration.
Cells bone marrow– SMxK (green)
capable of regenerating skin, including
including the top layer of the epidermis
(red).

28. Functions of attachment contacts:

Mechanically hold cells together
among themselves, with intercellular
matrix or basal
plate.
Stabilize the cytoskeleton, size and
cell shape; support
structural integrity of the tissue.
Provide motor reactions
cells (amoeboid movement).
Participate in cellular signaling.
Rice. Cytoskeleton of a keratinocyte.

29. Types of adhesive (attachment) contacts:

Adhesive
contacts are formed
between (1) adjacent
cells (desmosomes,
adhesion belts) or
between (2) cells and
intercellular
substance
(hemidesmosomes,
focal contacts).

30. Types of adhesive (attachment) contacts:

ICC
Cell + MO
Desmosome
Adhesion Belt
Hemidesmosome
Focal contact
Transmembrane proteins:
cadherins
integrins
Cytoskeletal proteins:
intermediate filaments
actin microfilaments

31. MECHANICAL MCC:

32.III. Communication contacts:

Communication
ICC
1. Slotted
contacts
(nexuses)
2. Synapses

33. 3.1. Gap contacts (nexuses):

Nexuses are a way
connections between cells
body with the help
protein channels
(connexons).
Through slots
contacts can
directly
transmitted from cell
to the cage small
molecules (with
molecular weight
up to approximately 1,000 D).
Gap junctions (nexes) provide ionic and
metabolic coupling (interaction) of cells.

34. 3.1. Gap contacts (nexuses):

Individual connexons
(several tens and hundreds)
focused on
limited in area
areas of membranes - plaques
(English plaque) with a diameter of 0.5-1
µm.
In the region of the membrane nexus
neighboring cells are brought closer together,
distance between them
is 2-4 nm.
Structural basis of the gap junction (nexus)
make up connexons - channels formed by six
connexin proteins.

35. Functions of slot contacts:

IN nervous system slotted
contacts is one way
transfer of excitation between
neurons (electrical
synapse).
Gap junctions in the heart
connect cardiomyocytes
to provide
contraction synchronicity
all cells of one section.
Electrical cell coupling

36. Electrical synapse...

37. Functions of slot contacts:

Gap contacts connect
follicle cells with oocyte and
the destruction of this connection is
one of the signals for ovulation
oocyte.
Chemical cell conjugation

38. Functions of slot contacts:

Significant role in
functioning
organisms play like this
called hemi-nexuses "halves" of the slots
contacts opened in
intercellular
space.
For example, they participate in
creating a calcium wave in
endothelium, releasing ATP from
cells, which contributes
maintaining blood
pressure in the vessel.

39. Purinergic system of regulation of functions

ATP molecule
previously known
just like
universal
intracellular
energy source,
also performs
communicative
functions.

40. Purinergic system of regulation of functions

ATP receptors are
sodium and
calcium channels.
ATP Regulated
increase in [Ca2+] in
cell calls like
short-term
(muscular
reduction) and
long term effects
(change in gene
expression and
for example, cellular
proliferation).

41. The effect of ATP on the circulatory system

ATP effect –
narrowing of the vessel
and blood pressure
At the synapses, SNSs are released into the cleft
ATP and neurotransmitter - norepinephrine.
ATP activates receptors on the walls
blood vessel and causes their rapid
narrowing → blood pressure increases.

42. The effect of ATP on the circulatory system

Increased blood flow
causes a shift
endothelial cells
vessel, which leads to
release of ATP,
which activates
receptors nearby
cells → NO secretion
→ dilation of the vessel
→ Blood pressure decreases.
ATP effect –
dilatation of the vessel
and ↓BP

43. In some cells, connexons can function independently of gap junctions.

Bone studies
cells* showed that
connexons can be
receptors for
antiapoptotic signals
(eg alendronate)
transducing signals
survival through
intracellular signaling
kinase/mitogen-activated pathway
protein kinase (ERK/MAPK).
* Nature Reviews Molecular Cell
Biology 4, 285 -295 (2003)

44. Connexons are “nonspecifically controlled” channels:

Connexons are

channels:
Various types of connections can interact with connexons.
proteins, such as kinases that phosphorylate
connexins and changing their properties, which can
regulate the work of the communication channel.

47. Bladder activity depends not only on the amount of drink, but also on the time of day.

Bladder activity does not depend
only on the amount drunk, but also on
time of day.
Most people have a bladder
behaves calmly at night, without waking up his family
owners at the slightest provocation.
Rice. Sleeping Japanese macaques.

48. Animal studies have shown that bladder capacity is regulated by the protein connexin-43.

Mice with increased level this protein
urinated more often: their bladder
reacted to less than usual
amount of liquid.
Connexin gene activity depended on time
days and was controlled by another protein, Rev-erbα,
directly related to the circadian
rhythm.

49. Animal studies have shown that bladder capacity is regulated by the protein connexin-43.

Connexins are short-lived and must be stored
be replenished all the time.
Obviously, an excess of connexin-43 proteins,
connecting cells of the bladder wall
make it tougher and more sensitive to
excess liquid. At night, protein production
falls and the bladder wall becomes
more elastic.

50. 3.2. Synapses are...

... specialized
intercellular
contacts,
providing
signal transmission
(nerve impulses)
excitable cells:
neurons,
muscle cells,
secretory cells.

51. Structure of a chemical synapse:

52. Synaptic transmission:

1) Synthesis and accumulation
neurotransmitter in the presynapse.
2) Secretion of a neurotransmitter in
synaptic cleft (exocytosis,
Ca2+).
3) Interaction
neurotransmitter with receptors
postsynaptic membrane.

53. Synaptic transmission:

4a). Membrane depolarization
(excitatory synapses) → specific
cell response: generation of a nerve impulse,
muscle contraction or secretion.
4b). Membrane hyperpolarization (inhibitory
synapses) → cessation of specific
processes in excitable cells.
5). Removing a neurotransmitter from
synaptic cleft to presynaptic
space: inactivation by enzymes or
translocation by special proteins.

54. Synaptic transmission of information signal:

55. Synaptic signal transmission

56. Blockade of synaptic transmission and its consequences.

Botulinum
and tetanus
toxins
block the process
exocytosis
neurotransmitters.

57. Blockade of synaptic transmission and its consequences:

Level Defects
conveyors
mediators
(norepinephrine and
serotonin) –
cause of mental
disorders,
For example,
manic-depressive
condition.
Neurotransmitter transporter blockers –
antidepressants, cocaine and amphetamines.

58. chemical synapses (clinical aspect):

Pilocarpine is an acetylcholine mimetic.
Pilocarpine is widely used for
treatment of glaucoma, because main with local
When used in the form of eye drops, it causes
constriction of the pupil and depression
intraocular pressure.
cholinomimetics
ACh + cholinergic receptors

It is worth noting the differences observed at this stage between regeneration and embryonic development. To implement regeneration, innervation is necessary. Without it, cell dedifferentiation can occur, but subsequent development is absent. During the period of embryonic morphogenesis of the limb (during cellular differentiation), the nerves are not yet formed.

In addition to innervation on early stage regeneration requires the action of metalloproteinase enzymes. They destroy matrix components, which allows cells to divide (dissociate) and actively proliferate. Cells in contact with each other cannot continue regeneration and respond to the action of growth factors. Thus, during regeneration, all variants of intercellular interactions are observed: through the release of paracrine factors diffusing from one cell to another, interaction through the matrix and through direct contact of cell surfaces.

During the dedifferentiation stage, homeotic genes are expressed in stump cellsHoxD8 AndHoxDlO, and with the beginning of differentiation - genesHoxD9 AndHoxD13. As was shown in section 8.3.4, these same genes are actively transcribed in the embryonic morphogenesis of the limb.

It is important to note that during regeneration, cell differentiation is lost, but their determination is preserved. Already at the stage of undifferentiated blastema, the main features of the regenerating limb are laid down. This does not require activation of genes that provide limb specification (Tbx-5 for front andTbx-4 for the rear). The limb is formed depending on the location of the blastema. Its development occurs in the same way as in embryogenesis: first the proximal sections, and then the distal ones.

The proximal-distal gradient that determines which parts of the growing bud will become a shoulder, which will become a forearm, and which will become a hand is set by the protein gradient Prod 1. It is localized on the surface of blastema cells and its concentration is higher at the base of the limb. This protein plays the role of a receptor, and the signal molecule (ligand) for it is a protein nAG. It is synthesized by Schwann cells surrounding the regenerating nerve. In the absence of this protein, which through ligand-receptor interaction triggers the activation of the cascade of genes necessary for development, regeneration does not occur. This explains the phenomenon of lack of limb restoration when a nerve is cut, as well as when an insufficient number of nerve fibers grow into the blastema. Interestingly, if the nerve of a newt's limb is retracted under the skin of the base of the limb, an additional limb is formed. If it is taken to the base of the tail, the formation of an additional tail is stimulated. Reduction of the nerve to the lateral region does not cause any additional structures. All this led to the creation of the concept regeneration fields.

Intercellular interactions are the interactions of cells with each other. Can be like distant, at a distance and contact. Distant interactions are carried out using soluble substances secreted by cells into their environment and affecting other cells. These substances are called mediators, or intermediaries. Hormones, biogenic amines, antibodies and many other biologically active substances can act as mediators; these substances affect the receptor apparatus of the cells with which the cell that released the mediator interacts. Consequently, distant intercellular interactions mediate the effect of hormones on cells and occur during the immune response and embryonic development (embryonic induction, see embryology) and in many other important cellular reactions.

In addition, in a multicellular organism, all cells are connected to each other using intercellular contacts (contact intercellular interactions). Contact interactions consist of several phases and include distant interactions as the initial stage:

1. Recognition by one cell of another cell (can be distant through mediators and contact through receptors).

2. Establishment of weak connections between cells.

3. Formation of stable intercellular contacts. The second and third phases are carried out using cell adhesion molecules.

All intercellular contacts are divided into three main types (Fig. 3.15, 3.16):

1. Adhesive contacts, which mechanically connect cells to each other. The main type of adhesive contacts are desmosomes. There are three types:

- punctate desmosomes (spot desmosomes). They hold cells together in separate places. At the same time, on the inner side of the cell membranes of two

cells there is an electromagnetic plate connected to a network of keratin microfilaments. These filaments end in the plate or extend along its surface. The adjacent plates of two cells are connected through the intercellular space by fibers of a protein of unknown nature. There is electron-dense material in the intercellular space;

- encircling desmosomes (zones of desmosomes). They run near the apical end of the cells along their perimeter in the form of a strip. This band consists of bundles of actin filaments localized on the cytoplasmic side. There is electron-dense material in the intercellular space;

- hemidesmosomes. They are like half of a punctate desmosome. Attach epithelial cells to the basement membrane.

Adhesion molecules, such as E-cadherin, dsmocollins, desmogleins, etc., play an important role in the functioning of adhesive contacts.

2. Tight contacts. This is a type of normally open contact. This type of contact not only mechanically connects cells with each other, but also prevents the passage of molecules between them. In tight contacts cell membranes approach each other at a distance of up to 5 nm and bind to each other using special proteins.

3. Conductive contacts. At these contacts, small molecules can be transferred from one cell to another. In this case, the membranes of two cells approach each other at a distance of up to 3 nm and form channels - connexons. Through connexons, free exchange of low-molecular substances (electrolytes, vitamins, nucleotides, ATP, sugars, amino acids, etc.) occurs between cells. Thus, this type of contact plays an important role not only in mechanical, but also in chemical communication of cells. An example of such contacts is gap junctions: nexuses between muscle cells in smooth and cardiac muscles. In this case, excitation is transferred from one cell to another. Second example - synapses- contacts between nerve cells.

In addition to these main types of intercellular contacts, there are also interdigitation- or interdigital connections, when the cytoplasm with the covering cytolemma of one cell in the form of a finger is wedged into the cytoplasm of another cell and vice versa. Interdigitation sharply increases the strength of intercellular connections, and in addition, increases the area of intercellular interactions, due to which the intercellular exchange of metabolites increases.

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