[Ultrastructure of specialized intercellular contacts]

The review contains some literary evidence and the authors' own data on the ultrastructure and molecular organization of specialized intercellular junctions (tight, septate, intermediate, gap junctions and desmosomes). The analysis of structural organization of junctions was carried out using data obtained by various electron microscopic techniques (ultrathin sections, freeze-cleaving, negative contrasting, optical diffraction of electron microscopic images), low-angle X-ray diffraction and biochemical methods. Some aspects of structural organization of specialized junctions providing for their functioning are concerned. Among other things, recent findings on the molecular structure of connexons and on their conformational changes promoting permeability regulation of their hydrophilic channels are reviewed. Available data on the lability of specialized junctions, both in the process of the organism's viability and during pathological states and after certain experimental treatment, are emphasized. Facts testifying to the lability of separate components of a junction including its perimembraneous cytoplasmic regions, are in a good agreement with a widespread liquid-mosaic model of the structural organization of cell membranes.