DESMOSOMES (grech, desmos communication, a sheaf + soma a body) — the structures providing communication between cells at metaphytes.
The greatest development of D. is reached in epithelial fabrics. Come to light on the adjoining surfaces of the next cells. Under a light microscope of D. have an appearance of the small phaeochrous little bodies which are often lying in the educations taken earlier for intercellular bridges. To them tonofibrils — the fine ends passing in cytoplasm of epithelial cells meet. Electronic microscopic examinations showed what in the area D. of continuous communication between cells does not exist. Consist of two symmetrically located half, between to-rymi the intercellular space remains; one half of D. belongs to one cell, another — next (fig.). Each of half, length apprx. 0,2 microns, includes the site of a cytoplasmic membrane — plasmolemmas and a layer of cytoplasm, adjacent to it. The cytoplasmic membrane in that part where it is D.'s part, is thickened and has an appearance of a tight homogeneous coat. Under a cytoplasmic membrane the layer is located with the knitting rich with mucopolysaccharides of cytoplasm, in Krom there is a dense attachable plate 15 — 20 nanometers thick. Tonofibrils which, having described loops in the form of wide arches, come back in cytoplasm approach this plate.
Width of intercellular space between D.'s half makes 20 nanometers and more. Sometimes in it note existence of the cement substance representing a lipidomukopolisakharidny complex on chemical structure. It is possible that the cement substance, covering with a thin coat a surface of cellular covers, strongly is connected with them. Thanks to it the distance between the next cells is reduced. Are not always constant structures. In the course of migration of cells, napr, in epidermis of skin, they continuously collapse and arise again. The main function D. — to provide mechanical communication between cells. Therefore in spite of the fact that D. consist of two half, in places where they are located, cells are connected among themselves most strongly. The tonofibrils which are coming to an end in D. serve as an intracellular support.
Except typical D., along a basal surface of epithelial cells so-called semi-desmosomes which on the ultrastructure are quite similar to D. sometimes come to light, but represent only their half.
The septirovanny D. having an appearance of bee cells are characteristic of cells of backboneless animals: cytoplasmic membranes of the next cells throughout 0,15 — 0,3 microns are connected by cross partitions — septa (outgrowths of a dense periblast of a cytoplasmic membrane). In septirovanny D. there are neither plates of an attachment, nor tonofibrils.
The hypotheses made for an explanation of the mechanism of strong coupling of cells, much. It agrees one of them, it occurs by direct chemical bonds between surfaces of cells as a result of a complementary arrangement on the next cellular surfaces of any active groups (SH-, - OH, - NH 2 etc.). Tyler and Weiss (A. Tyler, 1946; P. Weiss, 1947) suggested that chemical contacts between cells are similar to reaction antigen — an antibody (see Antigen antibody reaction).
According to other hypothesis it is supposed that at molecular level contacts of cells are made as calcic bridges. It is shown [to Gerbst (S. by Herbst), 1900] that the crushed eggs of a sea hedgehog placed in the water deprived of calcium ions are divided into separate blastomeres by simple stirring. Against this hypothesis there is a number of objections, in particular, that by theoretical calculations the space between cells shall not exceed 1 nanometer whereas actually it makes 20 nanometers and more. Was widely adopted physical. Curtice's hypothesis (A. Curtis, 1962) who assumed that forces of pushing away in the form of the negative charge inherent to a surface of the majority of cells, are counterbalanced with forces of an attraction — van-der-vaalsovymi by forces (see. Molecule ). At their expense the surfaces having a similar structure are attracted to each other and make a start if their structure differs. At the same time there are no direct proofs of action of van-der-vaalsovykh of forces in live systems yet. There are some more various hypotheses of D.'s nature, however each of them svoystven the common fault connected with lack of sufficient knowledge about thin physical. - chemical structure of the components forming D.
See also Cell .
Bibliography: Alov I. A., Braude A. I. and Aspiz M. E. Fundamentals of functional morphology of a cell, M., 1966; Velsh U. and Shtorkh F. Introduction to cytology and histology of animals, the lane with it., M., 1976; In about l to about in and O. V. and Tarabrin S. B. Embriogenez of the person and his regulation, page 44, M., 1973; Polikar A. Molecular cytology of membranes of a zooblast and its microenvironment, the lane with fr., Novosibirsk, 1975; it, Elements of physiology of a cell, the lane with fr., L., 1976, bibliogr.; Robertis E., Novinsky V. and With and e with F. Cytobiology, the lane with English, M., 1973; With u r t i s A. S. cell Contact and adhesion, Biol. Rev., v. 37, p. 82, 1962.
E. F. Kotovsky.