Electrical properties and cardiac myocyte structure
Burt B. Hamrell in Cardiovascular Physiology, 2018
Each myocyte is bounded longitudinally by intercalated discs and can branch (Figure 5.1). The intercalated discs connect myocytes end-to-end (Figure 5.1). Finger-like projections of the sarcolemma at the ends of myocytes are interlocked to form the intercalated disc. Desmosomes are dense areas of adherence within the intercalated disc (Figure 5.1). Desmosomes mechanically link myocytes and transmit force from one myocyte to the next. Of great importance are other specialized dense areas within the intercalated disc, the gap junctions (Figure 5.1), which have low electrical resistance (Figure 5.1). The gap junctions contain channel-like structures called connexins that are low resistance pathways from the end of one myocyte to the next interconnected myocyte. Ions move relatively freely from myocyte to myocyte through gap junctions. This accounts for the low myocyte-to-myocyte resistance and high conductance throughout heart muscle tissue.
Freeze Fracture in Lung Research
Joan Gil in Models of Lung Disease, 2020
Gap junctions represent transcellular channels that permit the exchange of small molecules and ions between adjacent cells (Gilula et al., 1972; Potter et al., 1966). While they are ubiquitous, not all epithelial and endothelial cells are linked by them at any given time. By freeze fracture, gap junctions are shown to form patches of closely packed membrane particles (connexons) that are in register with similar particles in the membrane of the adjacent cell (Fig. 1). Each connexon consists of protein subunits, arranged to form a central channel that allows electrical coupling and the exchange of molecules of up to 800-1,200 daltons. Permeability of the gap junction can be modulated by changes in pH, pCo2, Ca2+, or membrane potential. Studies of their structural organization within the membrane, their regulation, and biochemical composition are underway (for a review see Revel et al., 1985).
Role of Cell-to-Cell Coupling in Control of Myometrial Contractility and Labor
Robert E. Garfield, Thomas N. Tabb in Control of Uterine Contractility, 2019
Gap junctions are intercellular channels that link cells to their neighbors and allow the passage of inorganic ions and small molecules.56,72,75,80,89 They have been found between cells in every tissue and organ examined and are essentially ubiquitous in the animal kingdom. In electron micrographs of thin sections, they appear in regions of close opposition between cells as zones of paired, parallel membranes of unusually smooth outline separated by a narrow space of constant width—the gap—about 2 to 3 μ M (Figures 2 and 3). In freeze fracture replicas vertebrate gap junctions appear as arrays of 8 to 9.5-μ M membrane proteins organized into circular or oval plaques (Figures 4 and 5).
The role of connexins in breast cancer: from misregulated cell communication to aberrant intracellular signaling
Published in Tissue Barriers, 2022
Yagmur Ceren Unal, Busra Yavuz, Engin Ozcivici, Gulistan Mese
Both intrinsic and extrinsic factors have critical roles in breast cancer initiation and progression. Breast cancer grows into a complex microenvironment and crosstalk among cancer cells and between cancer cells and their microenvironment can alter cellular processes. Direct cell-to-cell contacts and communication in addition to signals delivered from the extracellular milieu greatly contribute to the management of cellular programs.7,8 Cell-to-cell interactions and communications can be mediated by cell adhesion proteins that form adherent junctions and tight junctions and by intercellular channels formed by gap junctions (GJ), respectively. Gap junction channels are composed of connexin subunits and facilitate the direct linkage between the cytoplasm of adjacent cells.9 Significant proportion of cellular communication in tissues is mediated by gap junctions and their aberrant expressions and/or functions are associated with hereditary genetic diseases and cancers.10 Alterations of gap junction channel activities, changes in localization and expression of connexins have been reported in various cancers including breast cancer,11–13 and this review will mainly focus on the roles of connexins and their channels in cancers with specific emphasis on breast cancers.
Targeting connexin hemichannels to control the inflammasome: the correlation between connexin43 and NLRP3 expression in chronic eye disease
Published in Expert Opinion on Therapeutic Targets, 2019
Odunayo O. Mugisho, Ilva D. Rupenthal, Francois Paquet-Durand, Monica L. Acosta, Colin R. Green
Gap junctions directly join two adjacent cells allowing the transfer of ions and molecules up to about 1500 Da [12]. Each gap junction channel is formed by the pairing or docking of two connexin hemichannels from adjacent cells. Prior to docking, hemichannels at the cell surface have a low open probability, indicated by low membrane permeability under normal physiological conditions [13]. When hemichannels open, they form a large nonselective membrane channel which has been termed a ‘pathologic membrane pore’ [13–15]. Connexin hemichannels open with injury or disease, responding to insults such as ischemia and inflammation. In vitro, for example, oxygen-glucose deprivation, metabolic inhibition, inflammatory cytokines and reduced extracellular Ca2+ all induce hemichannel opening [13,16–19]. Opening depolarizes the cell and in extreme cases will cause cell lysis [20–22]. Moreover, with opening there is an influx of Na+, Cl−, and Ca2+ as well as an efflux of K+ ions [23–26], glutamate, aspartate and ATP are released (from glial cells and neurons), and Ca2+ influx results in mitochondrial dysfunction and necrotic and apoptotic cell death [13,27,28]. Hemichannel opening can induce cytokine release [29]. These are all features that have now been associated with the inflammasome pathway.
Progress of co-culture systems in cartilage regeneration
Published in Expert Opinion on Biological Therapy, 2018
Jianyu Zou, Bo Bai, Yongchang Yao
Many researchers devote themselves to investigating the underlying mechanisms in direct co-culture systems. Some suppose that the direct cell-cell contact may result in the cell fusion of the different types of cells to form heterokaryons [36,86]. Some believe that direct physical contact facilitates the close intercellular communication and signal transmission among the co-cultured heterologous cells via autocrine and paracrine ways [34,87]. Some note that connexons, expressed by chondrocytes, form gap junctions and enhance cell signal exchange and further improve tissue formation [83,88]. Recently, a comprehensive study was carried out to determine the mechanisms behind co-culture systems [25]. This study employed a cytosolic dye transfer test and connexin 43 (a gap junction protein) staining to confirm that the communication between human articular chondrocytes and human bone marrow-derived MSCs in the direct co-culture system is through gap junctions. Gap junctions are of great importance in cell–cell connections by the exchange of nutrients and the transduction of molecular signals [89].
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