MUSCULAR TISSUE

From Big Medical Encyclopedia

MUSCULAR TISSUE (textus muscularis, LNH) — group of body tissues of the animals and the person having property of contractility. Allocate smooth and cross-striped M. to t.; the last is subdivided, in turn, on skeletal and cordial. Property of contractility also nek-ry specialized kinds of other fabrics — the myoepithelial fabric (an ectodermal origin) which is a part of trailer secretory departments (acinus) salivary both sweat glands, and M. of t have. a neuroglial origin, being a component of an iris (a sphincter and the dilator of a pupil).

In development of a question of the nature and M.'s origin of t. the big contribution was made by A. A. Zavarzin, N. G. Hlopin and other domestic scientists. Smooth M. of t. the person and vertebrate animals develops as a part of derivatives of a splanchnopleura — a visceral layer of splanchnotomes (see. Mesoderm ) and by the nature treats fabrics of internal environment of an organism. Skeletal M. of t. arises from a specific embryonal rudiment — the myotome which is a part of elements of the segmented mesoderm — somites (see), and also from a mesodermal rudiment — mesenchymas (see). Cordial M. of t. develops from a coelomic epithelium. For all M. of t. similar isolation as a part of an embryonal rudiment in the form of cells of a spindle-shaped form — myshtseobrazovatelny cells, or myoblasts is characteristic.

SMOOTH MUSCULAR TISSUE

Smooth M. of t. (textus muscularis nonstriatus) of the person and vertebrate animals creates muscular coats of internals and a wall of blood vessels.

A histogenesis

For an embryonal histogenesis of smooth M. of t. isolation among the mesenchyma surrounding the developing body or vessels (an intestinal tube, a trachea, bronchial tubes, ureters, an aorta, arteries, veins etc.), the spindle-shaped cells which are located usually in two layers (internal and outside muscular coats) is characteristic. In the course of smooth M.'s differentiation of t. smooth muscle cells — smooth myocytes (myocytus glaber), or leyomiotsita, approach and form dense structure, getting a specific definitivny form.

Structure

Fig. 1. Microdrugs of a muscular coat of intestines of a salamander (slit). Smooth muscular tissue in the weakened and reduced state: 1 — kernels; 2 — myofibrils.

In a muscular coat of the majority of internals smooth muscle cells have extended (from 15 to 500 microns) a spindle-shaped form. According to a form of a cell of a kernel are extended in length, irichy at reduction of a cell the kernel can get a shtoporoobrazny form from mammals. At nek-ry species of amphibians reduction of a smooth muscle cell is followed by compression of a kernel along an axis (fig. 1). Mitochondrions (see) in a smooth muscle cell concentrate around a kernel, and also along an axis of a cell. A smooth and rough cytoplasmic reticulum (see. Endoplasmic reticulum ) it is developed poorly.

Fig. 2. Volume scheme of ultrastructure of the site of smooth muscular tissue of vertebrata: and — muscle cells; — the small site of the cells represented on the scheme and (1 — kernels; 2 — a zone of close contact of cells; 3 — mitochondrions; 4 — a plasmolemma; 5 — emboly of a plasmolemma; 6 — a cytoplasmic reticulum; 7 — protofibrils).

According to a submicroscopy, the ultrastructure of smooth muscle cells is characterized by existence of numerous plazmo-lemmalny viyachivaniye like pinotsitoznykhpuzyrk (fig. 2). Assume that transfer in a cell of the irritation causing its excitement and reduction is connected with these embolies.

The specific structural character of a smooth muscle cell found by method of usual light microscopy is existence in cytoplasm of fine fibers — myofibrils, well distinguishable on the microdrugs painted by iron hematoxylin. On diffraction patterns comes to light that myofibrils consist of thinner fibrils — protofibrils, or myofilaments. Between cells smooth M.'s stroma of t is located. — the collagenic (reticular) and elastic fibers forming dense networks around each cell. It is proved that smooth muscle cells synthesize fibers of a stroma by means of a rough cytoplasmic reticulum.

Process of reduction in smooth M. of t. on the usual gistol, drugs painted by iron hematoxylin it is found on characteristic consolidations (strips of reduction) passing through many ranks of cells. On diffraction patterns reduction of smooth muscle cells comes to light a condensation of protofibrils.

CROSS-STRIPED MUSCULAR TISSUE

Cross-striped muscular tissue (textus muscularis transverso-striatus) is presented to skeletal and cordial M. by t.

Fig. 3. The process flow diagram of a differentiation of cross-striped muscle fibers in an embryogenesis: and — a stage of myoblasts (a part of myoblasts is in a stage of a mitosis); — merge of myoblasts in myotubes (are specified by an arrow); in — the created myotube; — muscle fiber: 1 — a central axial bunch of myofibrils, 2 — kernels of muscle fiber.

Skeletal muscular tissue

Skeletal muscular tissue [textus muscularis striatus (sceleti)]. Histogenesis. Main source of development of skeletal M. of t. in an embryogenesis — a mesoderm of somites, from a cut there are «fluid» (the bookmarks moving from the place to skeletal parts) bookmarks consisting of the mezenkhimny cells creating primary models of muscles on site of their differentiation. The differentiated mezenkhimny cell takes the spindle-shaped form of a myoblast characterizing the first (cellular) stage of a differentiation. The number of myoblasts increases due to mitotic divisions, and also as assume, by transformation of cells satellites (not numerous one-nuclear cells with the condensed arrangement of chromatin in a kernel and poor development of cytoplasmatic organellas). Upon transition to the following, the second stage of a differentiation mitotic divisions stop and myoblasts merge the ends, forming myotubes (myotubuli), in to-rykh a kernel hold central axial position (fig. 3). In a peripheral zone of myotubes fibrillar and membrane structures form. The differentiation of myoblasts and myotubes can occur also in culture of fabric out of an organism. However the third stage of a differentiation — transformation of myotubes into muscle fibers with a peripheral arrangement of kernels and a central axial arrangement of myofibrils can result only in an organism from interaction with motive nerve fibrils (see. Muscles ).

Structure

Fig. 4. The classical scheme of a structure of muscle fiber on Geydengayna: 1 — a disk A; 2 — a disk I; 3 — a partition of T (telophragma); 4 — a partition of M (mesophragma); 5 — sarcosomes; 6 — cross network; 7 — myofibrils.
Fig. 5. Diffraction pattern of a sarcomere: 1 — a sarcomere; 2 — a disk A; 3 — semi-disks; 4 — a telophragma; 5 — a mesophragma; 6 — thick (miozinovy) myofilaments; 7 — thin (octynic) myofilaments.

Skeletal M. of t. it is constructed of the extended multinuclear educations — cross-striped muscle fibers (Touho-fibra transversostriata), each of to-rykh has the form of the cylinder with the rounded or pointed ends, the average sizes of fibers (at mammals and the person) — to 80 microns in the diameter and to 12 cm in length. As a rule, at vertebrata each fiber makes a single yarn. The idiosyncrasy of cross-striped muscle fibers defined by a light microscope — the cross striation caused by alternation of strips, or disks, two-refractive (anisotropic) substance — disks A [stria A (discus A)] and the deprived dvuluchepre-lomleniye (isotropic) substance — disks I [stria I (discus I)] (fig. 4). Disks A and I are a part of the thin fibrils located along an axis of cross-striped muscle fiber — myofibrils (myofibril-lae transversostriatae), forming so-called sarcomeres (fig. 5). Borders of sarcomeres have an appearance of the thin partitions crossing disks I in transverse direction — telophragmas (telophragma), or partitions of T; on old terminology the line Z. Less accurately the partition passing across a disk A — a mesophragma (mesophragma) comes to light; on old terminology — a mesophragma. At amphibians, reptiles, birds, mammals and the person of a myofibril on cross sections have outlines of a circle or a polygon to dia. 1 — 2 microns. At many species of fish, and also at arthropods, for to-rykh cross-striped M. of t is characteristic., myofibrils differ in the flattened form and on cross sections have an appearance of the extended ovals. Cross-striped muscle fiber can be considered as a huge multinucleate cell which cytoplasm (called usually by a sarcoplasm) is pushed aside to the periphery by the myofibrils holding central axial position. At all vertebrata the flattened kernels of an ellipsoidal form are located on the periphery of fiber (the tsentralnoosevy arrangement of kernels is characteristic of bony fishes and arthropods).

Under a basal membrane of muscle fibers on diffraction patterns find cells satellites.

Fig. 6. Microdrug of muscular tissue of language of a salamander (cross-striped muscle fibers): and — fiber in the weakened state; — fiber at the beginning of reduction (1 — a kernel; 2 — a disk A; 3 — a disk I; 4 — a partition of T (telophragma); 5 — a disk A in a phase of splitting on two semi-disks; 6 — a strip of L).

Process of reduction of cross-striped muscle fibers at a research under a light microscope is characterized by shortening and a thickening of sarcomeres that is followed by redistribution of anisotropic and isotropic substances (fig. 6). Characteristic morfol, line of dynamics of reduction of a sarcomere consists in splitting of a disk A on two semi-disks, between to-rymi there is a light strip of N, or a light zone (stria L, zona lucida). In process of reduction of a sarcomere anisotropic substance disperses to the approaching telophragmas, forming as a result of this movement of a strip of reduction, the replacing disks I.

Fig. 7. Volume scheme of ultrastructure of a telophragma: thin myofilaments (1) meet the ends (2), forming the arches pointed at tops.

At electronic microscopic examination of cross-striped muscle fibers thin details of a structure of myofibrils were revealed and membrane structures, poorly distinguishable at a svetooptichesky research, are open. It became clear that cross-striped M.'s myofibrils of t. consist of ultrastructural fibrils — protofibrils, or myofilaments, two types: thick (apprx. 11 nanometers in the diameter) and thin (apprx. 5 nanometers). As a part of a sarcomere thick protofibrils are located in a zone of a disk A, thin — in a zone of a disk I, forming two semi-disks divided by a telophragma, is built regions by the ends of thin protofibrils meeting in the form of the pointed arches (fig. 7). By means of specific biochemical, methods of a research it is established that protofibrils are constructed of special myoproteoses — thick of a myosin, thin generally from actin. A structure of molecules of myoproteoses — see below, the section Biochemistry of Muscular Tissue.

Fig. 8. Membrane device of cross-striped muscle fibers: 1 — cross sections of myofibrils; 2 — a sarcolemma; 3 — a tubule of T-system; 4 — tanks of a sarcoplasmic reticulum; 5 — tubules of a sarcoplasmic reticulum (L-tubules); 6 — a cover of L-tubules; 7 — triads; 8 — mitochondrions; 9 — thin myofilaments; 1 about — thick myofilaments.

The membrane device of cross-striped muscle fibers forms a complex system, four main structural components are a part a cut: 1) sarcolemma (sarcolemma), or plasmolemma; 2) system of cross tubules (A T-tubule, channels of the CU is those we, from armor. transversus cross); 3) a sarcoplasmic reticulum (reticulum sarcoplasmaticum) consisting of two departments — the tsister-new, located in a zone disk I, and canalicular, making longwise the oriented network (L-tubules, from armor. longitu-dinalis longitudinal) in a zone of a disk A; 4) the typical cellular membrane components which are a part of a lamellar complex (Golgi's complex) and a cytoplasmic reticulum (ergastoplazma), located with hl. obr. in perinuclear area (fig. 8). The sarcolemma as a specific cover of cross-striped muscle fibers includes two structural components — internal, homogeneous, and outside, fibrous, on reactions on gistol, dyes close to collagen. At electronic microscopic examination it became clear that on actually cellular, or internal, the membrane having thickness, typical for cellular membranes (apprx. 7,5 nanometers) and structure, the membrane of amorphous structure containing polysaccharides to-ruyu often is located call a basal membrane. The basal membrane is covered by the cover consisting of fine collagenic fibers. The plasmolemma in zones of a telophragma forms finger-shaped embolies (a tubule of T-system) in fibers between myofibrils, surrounding each of them with a ring. On tubules of T-system the excitement extending on a plasmolemma reaches the sokratitelny devices located in fiber. Enter the most close connection of a tubule of T-system with tanks of a sarcoplasmic reticulum in a zone of a disk I where walls of tubules approach walls of tanks. On diffraction patterns profiles of cuts through areas of contact of tubules of T-system with tanks of a sarcoplasmic reticulum have an appearance of three pulled together cavities called by triads.

Tanks of a sarcoplasmic reticulum are located around myofibrils in the form of couplings, from to-rykh lengthways myofibrils the L-tubules forming network in a zone of a mesophragma depart. Along fibers between myofibrils, occupying with the most part one or two sarcomeres, are located mitochondrions (on old terminology of a sarcosome), to the Crimea closely prilezhat tubules of T-system. About kernels on diffraction patterns typical cytoplasmatic organellas are found: lamellar complexes (see. Golgi complex ), double membranes of ergasto-plasma, ribosomal complexes, free ribosomes (see), and also sometimes complexes of centrioles.

Nervous device of cross-striped M. of t. consists of afferent (sensitive) nervous structures — neuromuscular spindles, and also motor, or motive (efferent) structures — motor plates, or plaques. Neuromuscular spindles, iner-virutsya from sensitive neurons of spinal nodes and represent complex structures, to-rykh are a part specific changed (intrafusal — «intra spindle») the muscle fibers surrounded with a dense fibrous bag of a spindle-shaped form, and the innervating their nerve fibrils. Motor plates in skeletal muscles receive nervous impulses from motor-neurons of front horns of a spinal cord.

Further spread of activation on muscle fiber is connected with a plasmolemma and tubules of T-system, by means of to-rykh excitement covers internal sokratitelny structures of fiber.

Structurally functional types of muscle fibers

In skeletal muscles of vertebrata, including mammals and the person, distinguish two main types of muscle fibers: white, providing a bystry (phase) physical activity, and reductions, red, capable to long not oscillatory maintenance. Structure of almost all muscles mixed; in them there are both white, and red fibers. Preferential content of these or those fibers defines belonging of muscles to this or that type. White muscle fibers on the gistol, structure differ in the high content of myofibrils at rather small volume of a sarcoplasm, and also thinner telophragmas. Biochemical these fibers differ in absence or the insignificant maintenance of a myoglobin, from to-rogo coloring of muscles depends. Histochemical white muscle fibers differ in lack of triglycerides, and also high content of a glycogen and the glycolytic enzymes providing energy demands of fiber. The abundance of cytoplasmatic organellas, in particular mitochondrions in a sarcoplasm, and also availability of triglycerides is characteristic of red muscle fibers along with the high content of a myoglobin causing their red color.

Heart muscular tissue (textus muscularis cardiacus)

Histogenesis

Source of development of cordial M. of t. in an embryogenesis — a coelomic epithelium from which there is a mezenkhimny rudiment which is exposed to a differentiation in cordial M. of t. The myoblasts developing from a mezenkhimny rudiment turn into cordial muscle cells — cardiomyocytes (myocytus cardiacus) creating similarity of fibers, in to-rykh myoblasts do not merge in myotubes, and keep cellular structure, separating from each other inserted plates (see. Heart ).

Structure

Fig. 9. Scheme of the Diffraction pattern of the site of a cardiac muscle (longitudinal section): 1 — myofibrils; 2 — a disk A; 3 — a disk I; 4 — thick myofilaments; 5 — thin myofilaments; 6 — mitochondrions; 7 — an inserted plate; 8 — tubules of G-system; 9 — a sarcoplasmic reticulum.

Unlike skeletal cordial M. of t. it is constructed of the cells connected in network by means of the large branchings making similarity of muscle fibers. Owing to such arrangement cardiomyocytes have incorrectly cylindrical form with the step bases, to-rye on longitudinal gistol, cuts have an appearance of the step line — an inserted plate, or an inserted disk (discus intercalatus). Unlike skeletal M. of t. in cordial muscle cells of a kernel borrow tsentrat no-axial situation while myofibrils form the dense coupling around a nuclear zone extending to a plasmolemma. At gistol, a research by means of a light microscope cross striation of myofibrils seems same, as well as in myofibrils of a skeletal myotube. However electronic microscopic examination opens between them the nek-ry distinctions connected with a cellular texture of cordial M. of t. (fig. 9). T-system in cordial M. of t. it is developed more intensively: tubules vpyachivatsya together with a basal membrane in a sarcoplasm. Division of a sarcoplasmic reticulum on tsisterno-vy (adjacent to semi-disks I) and canalicular (located in a zone of a disk A) departments is expressed less considerably, than in skeletal M. to t.: each sarcomere is put into the coupling from the intertwining tubules with small tanks, to-rye form with tubules of T-system of a triad in a zone of telophragmas. Characteristic sign of cordial M. of t. — abundance of mitochondrions, to-rye are localized by chains between myofibrils, quite often being located in a sarcomere so that their ends adjoin to telophragmas. Cavities ergastoplaz-we, ribosomes and lamellar complexes are found hl. obr. about kernels. Due to the cellular texture of cordial M. of t. myofibrils are interrupted in zones of inserted plates where fine (octynic) ends form specific basic structures in the form of the pointed arches. More powerful system T - tubules and M.'s myofibrils of t. hearts, perhaps, it is connected with need of ensuring the increased durability of a cardiac muscle. On gistol, a picture of reduction cordial M. of t. it is similar to skeletal. Elektronnomikroskopichesky picture of reduction of cordial M. of t. it is treated from positions of the theory of sliding developed for skeletal M. by t.

Age changes

Specific feature of skeletal M. of t. consists in relative stability of its structural structure: the constant number of muscle fibers in each skeletal muscle is determined soon after the birth and remains prior to senile involution. Age changes of skeletal M. of t. are characterized by reduction of volume of muscle fibers. The same patterns, perhaps, extend also to cordial M. of t., for a cut age changes of volume of cardiomyocytes are also characteristic. Due to the dying off of separate muscle fibers in skeletal M. of t. and substitution by their connecting fabric at senile age elasticity and M.'s elasticity of t decrease. However in some cases (at correct a gigabyte. mode and adequate muscular activity) normal structure of skeletal and cordial M. of t. remains till an extreme old age.

Age changes of smooth M. of t. are studied insufficiently.

Changes of muscular tissue at morbid conditions

Smooth M. of t. covers of bodies of respiratory, digestive, urinogenital systems, and also a wall of blood vessels can be exposed patol, to changes of hl. obr. as a result of disturbance of nervous and endocrine regulation, and also vitamin, salt and a microelement-nogo of balance. Patol. smooth M.'s change t. (infiltration of smooth muscle cells fatty and limy inclusions) it is observed at atherosclerotic defeat of a wall of blood vessels. Smooth M.'s sites of t. malignancies under the influence of the general etiol, factors of tumoral growth can be exposed (see. Tumours ). Meet as benign tumors — leiomyomas (see), and malignant — leiomyosarcomas (see), coming from smooth M. of t. number of bodies: intestines, bronchial tubes, etc.

For skeletal M. of t. specific structural reaction to various disturbances of metabolism is characteristic: dystrophy of the myofibrillar and membrane device, emergence of fatty inclusions, vacuolation of a sarcoplasm and especially vitreous degeneration of muscle fibers which is expressed in development in them cross located glybok, strips and nodes (a so-called tsenkerovsky degeneration). The Denervatsionny atrophy of skeletal muscles at the first stage is characterized by increase in level of synthetic processes (increase in content of RNA), strengthening of plastic activity and structural changes typical for regeneration processes (transition of kernels to tsentralnoosevy situation, development of myoblasts, splitting of muscle fibers); at later stages there is a thinning of muscle fibers, obesity of a sarcoplasm, dystrophy of muscle fibers to the subsequent substitution by connecting fabric. The Denervatsionny atrophy of skeletal muscles at the first stage at corresponding to lay down. actions it is reversible. Postdenervatsion-nomu hl are exposed to recovery. obr. motor plates. According to R. P. The Geneva (1974) neuromuscular spindles after a long denervatsionny atrophy are not recovered.

Cordial M. of t. reacts specific structural changes to various pathogenic influences, including steady gi-perfunktsionalny stress, a cut can cause cordial M.'s hypertrophy of t., expressed to hl. obr. in a thickening of muscle fibers. At systematic poisoning (e.g., alcohol, nicotine) observe fatty dystrophy of a stroma of cordial M. of t.

At the experimental heart attack caused by bandaging of coronal vessels characteristic ischemic changes of cordial M. of t are observed.: swelling and destruction of mitochondrions, superreduction of sarcomeres (high extent of their shortening) with disorganization of the protofib-rillyarny device and sarkotubu-lyarny system. Both in skeletal, and in cordial M. of t. can be observed as high-quality (see. Myoma , Rhabdomyoma ) and malignant (see. Rhabdomyosarcoma ) new growths.

Plastic activity of muscular tissue is expressed in processes primary (embryonal) and secondary (regeneration, transplant, renervatsionny, hyper functional) a histogenesis. Smooth M. of t. has rather high plastic properties providing a possibility of regeneration at its damages. Demonstrative example of high plastic activity of smooth M. of t. the hyperplasia of a smooth muscle wall of a uterus at pregnancy is. In an experiment it is proved that in this state smooth M. of t. a uterus, postponed by autotransplantation in the crushed view of the place of a remote skeletal muscle, can create smooth muscle model of a skeletal muscle. In this case the muscle consists of the smooth muscle cells forming similarity of the skeletal muscle connected by means of sinews with certain points of a skeleton in a form; sinews, obviously, form both fibroblasts, and smooth muscle cells.

Question of a way of self-updating of smooth M. of t. it is insufficiently studied. A. A. Zavarzin's school developed a hypothesis of the cambial mechanism of this process (smooth M.'s differentiation of t. occurs at the expense of special cambial cells of the connective tissue nature). During the studying of regeneration of smooth muscular tissue in an experiment mitotic divisions of smooth muscle cells are observed.

As it is established in an experiment by A. N. Studitsky, A. R. Strigano-va (1951), A. N. Studitsky (1959, 1978), R. P. Geneva (1974), regeneration and transplant activity of cross-striped M. of t., contrary to old ideas of low level of its plastic properties, it was very high.

Difficulty of direct use of the methods of a free autoplasty of M. of t developed in an experiment. in surgical practice consists in insufficient study of specific plastic properties of skeletal M. of t. person. The tests developed in an experiment for testing of plastic activity of M. of t. (autotransplantation of the t crushed by M. under skin, M.'s denervation reinnervation of t., stimulation of secondary development of M. of t. introduction to a diet of Thyreoidinum raising standard metabolism), demand a special research in relation to a human body. Experience comparative (on different types of animals) studying of a free autoplasty of muscles (or in the crushed state, or after preliminary denervation or traumatization) showed that M. of t. dogs has high plastic activity. By means of the methods of preparation of M. of t stated above. at dogs it is possible to replace large (to 7 cm in length) fragments of muscles that provides a complete recovery of their function.

On the representations existing earlier, cordial M. of t. has low plastic activity; the fact that nekrotizirovanny sites of cordial M. of t was considered as the proof of this situation., resulting from a heart attack, are replaced with connecting fabric.

However by a number of researchers it is established that cordial M. of t. possesses the specific mechanism of self-recovery, to-ry it is provided, on the one hand, with the connective tissue framework replacing the site of the t damaged by cordial M. during rather short term. (e.g., омертвев^ shiya as a result of a heart attack) the working hypertrophy and a hyperplasia of the remained sites of a cardiac muscle arises a connective tissue hem, and more slowly reacting to damage by the block actually of cardiomyocytes for the account to-rykh. Essential role in cordial M.'s self-updating t. the intracellular regeneration of cardiomyocytes including gradual replacement of the cytoplasmatic and nuclear organellas functioning a certain term neogenic plays (both by their reproduction and growth, and by molecular reorganization).

BIOCHEMISTRY of MUSCULAR TISSUE

Chemical composition of skeletal muscular tissue

In skeletal M. of t. mammals from 72 to 80% of water, apprx. 20 — 28% of weight of M. of t contain. makes a solid residue, hl. obr. proteins. In addition to proteins, in M.'s structure of t. extractive nitrogen-containing substances, nitrogen-free substances (a glycogen and other carbohydrates, various lipids, salts of organic matters, etc.), and also salts inorganic to - t and other chemical connections (tab. 1) enter.

Skeletal M.'s proteins of t. are divided into three basic groups: sarcoplasmic, myofibrillar and proteins of a stroma. According to H. N. Yakovleva (1974), falls to the share of sarcoplasmic proteins apprx. 35%, myofibrillar — 45% and proteins of a stroma — 20% of all myoproteose. The specified groups of proteins differ from each other on water solubility and salt environments with various ionic strength of solution markedly (half-sums of works of concentration of each ion on a square of its charge).

Sarcoplasmic proteins are dissolved in water and in salt environments with low ionic strength. The division of sarcoplasmic proteins existing earlier on mio a gene, globulin X, myoalbumin and proteins pigments is denied by a number of authors. The term «myogen» is collective. In particular, the series of compounds, allocated with enzymatic activity, napr, enzymes of glycolysis is a part of proteins of group of myogen { zymohexase, a glitseraldegid-3-phosphate-dehydrogenase, a glitserol-3-phosphate-dehydrogenase, phosphorylase, a lactate dehydrogenase, etc.). At salt fractionation also the myoalbumin close or even identical on the properties to albumine of blood serum gets to fraction of miogenovy proteins. Carry also dnkhatelny pigment to sarcoplasmic proteins myoglobin (see) and the various enzymes localized by hl. obr. in mitochondrions and the catalyzing processes of tissue respiration, oxidizing phosphorylation, and also nek-ry reactions of nitrogen and lipidic metabolism. Faces (P. Lehky, 1974) and others discovered new group of sarcoplasmic proteins — parvalbumina, to-rye are capable to connect calcium ions, however fiziol, the role of parvalbumin remains insufficiently clear.

Myofibrillar proteins — a myosin, actin and actomyosin are dissolved in salt environments with high ionic strength. Also so-called regulatory proteins — tropomyosine, troponin, and-aktinin, r-aktinin, forming in a muscle with actomyosin a uniform complex concern myofibrillar squirrels.

The main myofibrillar protein — a myosin makes 50 — 55% of dry weight of myofibrils. V. A works. Engelgardt and M. N. Lyubimova it is shown that the myosin has ATF-aznoy activity, i.e. is enzyme with ability to catalyze splitting of ATP on ADF and phosphoric to - that. The chemical energy of ATP which is released during the enzymatic reaction going with the participation of a myosin turns into mechanical energy of the reduced muscle. Relative pier. the weight (weight) of a myosin of skeletal muscles of the person apprx. 500 000. The molecule of a myosin possessing the extended form (length of its 150 nanometers) consists of two heavy polypeptide chains with relative a pier. weighing 205 000 — 210 000 and several short light chains with relative a pier. it is powerful apprx. 20 000. Heavy chains form long twirled and - a spiral («tail» of a molecule), the end of each heavy chain together with light chains creates a globule («head» of a molecule) capable to connect to actin. These heads are given from the main core of a molecule. The light chains which are in a head of a miozinovy molecule and taking part in manifestation ATF-aznoy of activity of a myosin, geterogenna on amino-acid structure. Quantity of light chains in a molecule of a myosin at different types of animals and in different types of muscles unequally. The molecules of a myosin definitely oriented in space form so-called thick miozinovy threads (thick myofilaments) in a sarcomere.

The actin making apprx. 20% of dry weight of myofibrils open F. Shtraubom in 1942, exists in two forms: globular actin (G-actin) and fibrillar actin (F-actin). Molecule of G-actin with relative a pier. weighing 42 000 consists of one polypeptide chain, 374 amino-acid rests take part in education a cut. The F-actin which is a product of polymerization of G-actin has structure of a dvukhtyazhevy spiral, details a cut are found not quite out.

At muscular contraction the myosin enters connection with F-actin, forming a new proteinaceous complex — actomyosin. The last has ATF-aznoy activity. However ATF-aznaya activity of actomyosin differs from ATF-aznoy activities of a myosin: actomyosin is activated by ions of magnesium and inhibited by ethylene diamine tetraacetate (EDTA) and ATP in high concentration whereas mgozinovy ATP-ase is inhibited by ions of magnesium, EDTA is activated and not inhibited by high concentration of ATP. Optimum pH values for both ATP-ases are also various.

The contained in myofibrils tropomyosine, troponin and nek-ry other regulatory squirrels directly participate in regulation of process of muscular contraction. A molecule of tropomyosine, open Bailey (To. Bailey) in 1946, consists of two and - spirals and has an appearance of a core 40 nanometers long; relative pier. weight of tropomyosine 65 000. Falls to the share of tropomyosine apprx. 4 — 7% of all miofpbrillyarny proteins. Troponpn — globular protein, open S. Ebashi in 1963; its relative pier. weight apprx. 80 000. In skeletal muscles of the person troponin makes only apprx. 2% of all miofpbrillyarny proteins.

Troponin, connecting to tropomyosine, forms the complex called Ebasi native tropomyosine. This complex is attached to octynic filaments and gives to actomyosin of skeletal muscles of vertebrata sensitivity to calcium ions.

It is shown that troponin it is capable to be phosphorylated with the participation of the protein kinases dependent on a cyclic adenozin-Z', 5' - monophosphate (tsAMF). The question of whether phosphorylation of a tropo-nin in a complete organism has relation to regulation of muscular contraction, remains still not clear.

Proteins of a stroma in skeletal M. of t. are presented generally collagen (see) and its derivatives, and also elastin (see). Stroma of skeletal M. of t., remaining after exhaustive extraction of muscular homogenate salt solutions with high ionic strength, consists considerably of connective tissue elements of a wall of vessels and nerves, and also a sarcolemma and nek-ry other structures.

Extractive nitrogen-containing substances of skeletal M. of t. are presented by adipic nucleotides — ATP, ADF and AMF (see. Adenozinfosforny acids ), nucleotides of a neadenino-vy row, creatine phosphate, creatine, creatinine, carnosine, anserine, free amino acids, etc. By data I. I. Ivanova (1969), the maintenance of adipic nucleotides in skeletal M. of t. a rabbit (in µmol! of crude weight of fabric) makes: ATP — 4,43; ADF — 0,81; AMF — 0,93. The maintenance of nucleotides of a neadeninovy row in M. of t. in comparison with quantity of adipic nucleotides it is not enough.

On a share of nitrogen creatine (see) and creatine phosphate (see. Phosphagens ), according to D. L. Ferdman (1966), about 60% of nonprotein nitrogen of muscles are necessary. Creatine phosphate and creatine participate in the chemical processes connected with muscular contraction.

Imidazolsoderzhashchy dipeptides — carnosine (see) and its metilirovanny derivative anserine (see) — are capable to recover operability of the tired muscles and to influence transfer of nervous impulses from a nerve on muscles.

From free amino acids in M. of t. concentration is highest glutamic acid (see) — apprx. 120 mg / 100 ml and its amide glutamine (see) — 80 — 100 mg / 100 ml. In M. of t. a number contains phosphatides (see): phosphatidylsincaline, phosphatidylethanolamine, fosfatidil-serine, etc.

These connections play an important role in M.'s structure of t., being a part of cellular membranes. Phosphatides take part also in exchange processes, in particular as substrates of tissue respiration. Other nitrogen-containing substances M. of t.: urea, uric to - that, adenine, guanine, xanthine and hypoxanthine — contain in small concentration and, as a rule, are either intermediate, or end products of a nitrogen metabolism.

Nitrogen-free substances of skeletal M. of t. are presented generally glycogen (see); its concentration fluctuates from 0,3 to 3% in terms of crude weight. The tenth and 100-th shares of percent fall to the share of other representatives of carbohydrates. In M. of t. find only traces of free glucose and very few geksozofosfat. In the course of metabolism of glucose, and also amino acids in M. of t. are formed milk, Pyroracemic and there are a lot of others carboxylic to - t. Neutral fats and cholesterol are found also in this or that quantity.

Inorganic salts in skeletal M. of t. contain in a type of ions. Among cations have the greatest concentration potassium (see) and sodium (see). Potassium of hl. obr. it is concentrated in muscle fibers, and sodium is preferential in intercellular substance. Much lower in skeletal M. of t. content of magnesium, calcium and iron; in M. of t. contain also microelements (see) — cobalt, aluminum, nickel, boron, zinc, etc.

Some features of chemical composition of smooth and heart muscular tissue at mammals. The t given about chemical structure of smooth and cordial M. are received generally on a lab. animals; information about chemical structure of these groups M. of t. at the person are very limited. Cordial M. of t. on the maintenance of a number of chemical connections the t is intermediate between skeletal and smooth M. So, the general content of protein nitrogen in skeletal M. of t. a rabbit — 30 — 31 mg/g of fabric, in a myocardium — apprx. 23,5 mg/g, and in smooth muscles of a uterus (myometrium) — within 20,3 mg/g of fabric.

Cordial and especially smooth M. of t. contain in comparison with skeletal M. of t. it is less than miofpbrillyarny proteins. So, the content of myofibrillar proteins (in mg of nitrogen on 1 g of fabric) in skeletal muscles of a rabbit 17,31, in a myocardium — 7,32, and in myometriums — 3,90. Concentration of proteins of a stroma in a myocardium and smooth M. of t. above, than in skeletal muscles.

By data I. I. Ivanova (1961), falls to the share of nitrogen of proteins of a stroma in skeletal muscles of a rabbit 10,1% of the general nitrogen M. of t., in a myocardium — 28,2%, and in myometriums — 40,4%. In a muscle of a left ventricle of heart the maintenance of myofibrils of yarny proteins, in particular actomyosin, is much higher, than in auricles and in tissue of a myocardium in general that, undoubtedly, is connected with more expressed sokratitelny function of this department of a myocardium. There are features and in fractional composition of sarcoplasmic proteins of a myocardium; so, proteins of group of myogen in percentage terms contain a little, but the content of myoalbumin is more, than in a sarcoplasm of skeletal muscles.

Content of ATP in cordial M. of t. (2,60 µmol! of fabric) below, than in skeletal (4,43 mkmol/g), and above, than in smooth M. of t. (1,38 µmol! г). It is established that the content of ATP and creatine phosphate is unequal in various departments of a myocardium. In walls of the ventricles of heart performing considerable work, these vysokoergichesky connections ensuring muscle work energy contain 40% more, than in auricles.

On the maintenance of a glycogen, carnosine and anserine cordial M. of t. also the t is intermediate between skeletal and smooth M. Concentration an imidazole - the containing dipeptides in a myocardium apprx. 10 mg / 100 ml, in smooth M. of t. only traces of anserine and carnosine are found.

There is a certain dependence between the nature of activity of muscles and content of phospholipids. Myocardium in comparison with skeletal and smooth M. of t. richer with phospholipids (tab. 2), oxidation to-rykh, invisible, delivers a considerable part of the energy necessary for its reduction.

Change of chemical composition of skeletal muscular tissue of mammals in ontogenesis

Embryonal skeletal M. of t. on chemical structure the t considerably differs from skeletal M. adult individuals. Muscles of embryos contain more water, than in functionally mature M. of t. Respectively the general protein content in M. of t. embryos (in terms of crude fabric) it appears lower, than in muscles of animals of the same look in the post-natal period of development. At a chicken embryo on 1 g of crude M. of t. 10 mg, and at four day chickens of 32 mg of protein nitrogen are necessary. In comparison with M. of t. in functionally unripe muscle the content of myofibrillar proteins (a myosin and actomyosin) and above — proteins of a stroma, and also myoalbumin and other proteins is lower than an adult organism. In process of fetation the content of myofibrillar proteins increases and increases ATF-aznaya activity in muscular extracts.

For embryonal M. of t. high content of nucleoproteids, and also ribonucleic and deoxyribonucleic to - t is characteristic. In process of development of an embryo the content of nucleoproteids and nucleinic to - t in M. of t. quickly decreases. Makroergichesky connections (ATP and creatine phosphate) in functionally unripe M. of t. it is much less, than in muscles of mature individuals. Imidazolsoderzhashchy dipeptides (anserine and carnosine) appear as a part of M. of t. during strictly certain period of ontogenesis; time of their emergence is closely connected with the beginning of motive function, formation of the reflex arc providing a possibility of a motive reflex, emergence calcium sensitivity of actomyosin and the beginning of operation of «ionic pumps» (see. Transport of ions ). There are also idiosyncrasies in fermental and isofermental ranges of embryonal M. of t. So, it is established that during ontogenesis the isofermental range changes lactate dehydrogenases (see); in skeletal muscles 3 — a 5-month embryo of a share of isoenzymes of a lactate dehydrogenase — LDG3 and LDG2 is the share respectively 40 and 31% of the general activity of a lactate dehydrogenase. In the course of embryonic development in skeletal muscles there is a gradual increase of activity of isoenzymes of LDG4 and LDG5 and decrease of the activity of isoenzymes of LDG1, LDG2 and LDG3 so at adult individuals in skeletal muscles isoenzymes of LDG5 and LDG4 have the greatest activity already.

The functional biochemistry of cross-striped muscular tissue

the Main function of muscles is reduction. At the same time the work connected with transformation of chemical energy in mechanical is carried out (see. Mekhanokhimichesky processes ). Muscle fiber is capable to be reduced only in the presence in the environment of ATP and a certain ion concentration of calcium. Under the influence of nervous impulse in muscle fiber there is a change of permeability of intracellular membranes and as a result of it is an exit in interfibrillar space from tanks and tubules of a sarcoplasmic reticulum and T-system of a quantity of calcium ions, to-rye communicate with troponiny. Conditions for interaction of actin with a myosin with formation of an aktomiozinovy complex are as a result created. At the same time due to energy of ATP sliding of octynic threads along miozinovy is carried out, i.e. happens muscular contraction (see). Then there steps dissociation of actomyosin on a myosin and actin, and the new act of «charging» (phosphorylation) of a myosin by its interaction at the same time begins with ATP in the presence of ions of magnesium.

Sources of energy of muscle performance

the Sokratitelny device of a muscle cell is provided with enough energy in the form of ATP due to continuous resynthesis of this makroergichesky connection which happens first of all owing to transphosphorylation of ADF creatine phosphate. This reaction kataliziruyetya enzyme creatine kinase:

The Kreatinkinazny way of resynthesis of ATP is extremely bystry and the most effective (at the expense of each molecule of creatine phosphate molecule ATP is formed). For this reason a number of researchers did not manage to determine long time decrease in concentration of ATP and respectively strengthening of ADF even at rather long tetanus. Only having applied specific inhibitor of a creatine kinase (1-fluorine-2,4-d1 nitrophenol), and also the agents interfering oxidative transformation of ADF into ATP, D. Cain and soavt. (1962) could show direct disintegration of ATP with a simultaneous gain of inorganic phosphate and ADF at single reduction of the isolated muscle of a frog. These results in further were confirmed with some other authors.

Nek-roye the amount of ATP can resintezirovatsya during adenilatkinazny (miokinazny) reaction:

For any fabric, including and muscular, are available two fundamental biochemical, process, in the course to-rykh high-energy phosphoric connections are generated. One of these processes — glycolysis (see), another — tissue respiration (see. biological oxidation ). The most important and effective of them is tissue respiration. At sufficient supply with oxygen the muscle, despite the anaerobic mechanism of reduction, finally works due to the energy which is formed during aerobic oxidation both decomposition products of carbohydrates, and some other substrates of tissue respiration, in particular fat to - t, and also acetate and acetoacetate (see. Tricarboxylic acids cycle ).

There are data proving that creatine phosphate in cordial M. of t. it is capable to carry out a role not only some kind of depot of easily mobilized makroergrshesky phosphatic groups, but also to play also a role of a transport form of the energy-rich phosphatic bonds which are formed in the course of tissue respiration and the related oxidizing phosphorylation. According to the concept offered by V. A. Saks, etc. (1975) transfer of energy in cytoplasm of a cell of a myocardium comes from mitochondrions according to the following scheme: The ATP which is formed as a result of oxidizing «phosphorylations and getting to a matrix of mitochondrions is transferred through an inner membrane of mitochondrions with participation specific ATP — ADF-translocases to an active center of a mitochondrial pzoferment of a creatine kinase, to-ry is located on outer side of an inner membrane; in an intermeme - abusive space (in the presence of ions of magnesium) in the presence in the environment of creatine equilibrium triple enzyme - a substrate complex — creatine - kreatinkina - for — ATP — Mg is formed 2+  ; this complex then breaks up with formation of creatine phosphate and ADF — Mg 2+ . Creatine phosphate diffuses in cytoplasm where it is used in myofibrillar kreatinkinazny reaction for a refosforilirovaniye of ADF formed in the act of reduction. Are suggested that not only in cordial, but also in skeletal M. of t. the similar way of transport of energy from mitochondrions to myofibrils takes place.

During the moderate work the muscle can cover the metabolic cost due to aerobic metabolism. However at big loadings when the possibility of supply with oxygen lags behind the need for it, for muscles the hl a political way of supply with energy is used. At hard muscular work the speed of splitting of a glycogen or glucose with education milk to - you increase in hundreds of times. The respectively contents milk to - you in M. of t. about 100 — 120 mg in 100 ml and can increase above. Milk to - that with a blood flow in a significant amount comes to a liver where due to energy of oxidizing processes it resintezirutsya in glucose and a glycogen (gluconeogenesis).

The listed mechanisms of resynthesis of ATP at muscle performance turn on in strictly certain sequence. The most emergency is creatine kinases-ny the mechanism, and only after — 20 sec. of hard work begin strengthening of glycolysis, this process reaches a maximum in 40 — 80 sec. At less hard work bigger value gets an aerobic way of resynthesis of ATP.

Content of ATP and creatine phosphate in cordial M. of t. below, than in skeletal muscles, and the consumption of ATP is very big therefore resynthesis of ATP in a myocardium takes place much more intensively, than in skeletal M. t. For a cardiac muscle of hematothermal animals and the person the main way of formation of high-energy phosphoric connections is the way oxidizing phosphorylations (see), connected with oxygen absorption. Regeneration of ATP in the course of anaerobic splitting of carbohydrates has no (glycolysis) in heart of the person of practical value. For this reason the cardiac muscle is very sensitive to a lack of oxygen. Idiosyncrasy of a metabolism of cordial M. of t. in comparison with skeletal is as well the fact that aerobic oxidation of substances of not carbohydrate nature during the work of a cardiac muscle has bigger value, than at reduction of a skeletal muscle. Only 30 — 35% of the oxygen absorbed by heart are normal, is spent for oxidation of carbohydrates and products of their transformation. The main substrate of breath in a cardiac muscle are fat to - you. Oxidation of not carbohydrate substances normal provides apprx. 65 — 70% of need of a myocardium for energy. However at increase in level of carbohydrates in blood (e.g., right after food) consumption by their cardiac muscle increases. The consumption of oxygen on oxidation of carbohydrates sharply increases, and oxidation rate fat to - t in a myocardium decreases. On the contrary, on an empty stomach and at starvation energy demands of heart generally become covered due to oxidation fat to - t.

Biochemical changes in skeletal muscular tissue at pathology

the General for the majority of diseases of muscles (the progressing muscular dystrophies, an atrophy of muscles because of their denervation, a polymiositis, damages of muscles at nek-ry avitaminosis, etc.) falloff in muscles of content of myofibrillar proteins, increase of concentration of proteins of a stroma and nek-ry sarcoplasmic proteins, including myoalbumin is. Along with change of fractional composition of myoproteoses at damages of muscles decrease in concentration of ATP and creatine phosphate is observed. Also decrease ATF-aznoy in activity of sokratitelny proteins (myosin), reduction of contents an imidazole - the containing dipeptides is noted. Consider that decrease in content of anserine and carnosine is connected! not with disturbance of biosynthetic processes, and with strengthening of disintegration of dipeptides.

At the progressing muscular dystrophies and other diseases of the muscles tied with disintegration of muscular tissue shifts in phospholipidic structure of muscles often are noted: considerably the maintenance of a fos-fatidilkholin and phosphatidylethanol-amine decreases, concentration of sphingomyelin and a lizofosfatidilkholina increases. Mechanisms of change of phospholipidic structure of M. of t. at pathology are not found out yet, also the role of these shifts in a pathogeny of muscular dystrophies is unknown.

For many forms of pathology of M. of t. disturbance of metabolism of creatine and its strengthened allocation with urine is characteristic — creatinuria (see). The question of the reasons of a creatinuria at diseases of muscles cannot be considered as finally solved still. The creatinuria at patients with a myopathy, perhaps, is result of disturbance in skeletal M. of t. processes of fixing (deduction) of creatine and its phosphorylation. As a result of disturbance of process of synthesis of creatine phosphate also creatinine is not formed; keeping of the last in urine sharply decreases. Owing to a creatinuria and disturbance of synthesis of creatinine the creatinine coefficient sharply raises (see. Creatine ).

At M.'s pathology of t. it is possible to observe a certain pattern in change of activity of enzymes in muscles: activity of the enzymes localized in a sarcoplasm decreases; slightly activity of the enzymes connected with mitochondrions changes; considerably activity of lizosomalny enzymes increases. At last, it is shown that at many diseases of muscular system there come shifts in system of cyclic adenosinemonophosphate (tsAMF): in M. of t. the maintenance of tsAMF decreases, activity of phosphodiesterase increases, and ability of adenylatecyclase to be activated under the influence of adrenaline and sodium fluoride is broken.

Tables

&Tablntsanbsp; 1. Chemical composition of skeletal muscular tissue of mammals (according to I. I. Ivanov, 1974)



Table 2. Content of phospholipids in different types of muscular tissue of a rabbit





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A. H. Studitsky; B. F. Korovkin (biochemical).

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