Gap junctions in the differentiated neural retinae of newly hatched chickens

1976 ◽  
Vol 22 (3) ◽  
pp. 597-606
Author(s):  
H. Fujisawa ◽  
H. Morioka ◽  
H. Nakamura ◽  
K. Watanabe
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Tight Junctions ◽  
Thin Section ◽  
Outer Nuclear Layer ◽  
Double Cone ◽  
Linear Arrays ◽  
Intramembrane Particles ◽  
Plexiform Layers ◽  
Membrane Region

Gap junctions in the neural retinae of newly hatched chickens were examined in thin section and by freeze cleaving. Unusual gap junctions containing linear arrays of intramembrane particles are found between principal and accessory cones which form a double cone at the region of the outer limiting membrane. These unusual gap junctions are often continuous with macular aggregates of hexagonally packed intramembrane particles which are characteristic of a typical gap junction. Typical gap junctions are also found in both the outer and the inner plexiform layers and in the outer nuclear layer, but are not so abundant as in the outer limiting membrane region. The sizes of intramembrane particles and their centre-to-centre spacing within the macular aggregate of a gap junction in differentiated neural retinae are slightly larger than those in undifferentiated neural retinae. Tight junctions are not found in differentiated neural retinae.

Tight and gap junctions in the intestinal tract of tunicates (Urochordata): a freeze-fracture study

1986 ◽  
Vol 84 (1) ◽  
pp. 1-17
Author(s):  
N.J. Lane ◽  
R. Dallai ◽  
P. Burighel ◽  
G.B. Martinucci
Keyword(s):  
Gap Junctions ◽  
Tight Junctions ◽  
Thin Section ◽  
Intestinal Tract ◽  
Freeze Fracture ◽  
Intestinal Cells ◽  
Fracture Profile ◽  
Tracer Studies ◽  
Septate Junctions ◽  
Fracture Study

The intestinal tracts from seven different species of tunicates, some solitary, some colonial, were studied fine-structurally by freeze-fracture. These urochordates occupy an intermediate position phylogenetically between the vertebrates and the invertebrates. The various regions of their gut were isolated for examination and the junctional characteristics of each part investigated. All the species examined exhibited unequivocal vertebrate-like belts of tight-junctional networks at the luminal border of their intestinal cells. No septate junctions were observed. The tight junctions varied in the number of their component strands and the depth to which they extended basally, some becoming loose and fragmented towards that border. The junctions consisted of ridges or rows of intramembranous particles (IMPs) on the P face, with complementary, but offset, E face grooves into which IMPs sometimes fractured. Tracer studies show that punctate appositions, the thin-section correlate of these ridge/groove systems, are sites beyond which exogenous molecules do not penetrate. These junctions are therefore likely to represent permeability barriers as in the gut tract of higher chordates. Associated with these occluding zonular junctions are intermediate junctions, which exhibit no identifiable freeze-fracture profile, and macular gap junctions, characterized by a reduced intercellular cleft in thin section and by clustered arrays of P face particles in freeze-fractured replicas; these display complementary aggregates of E face pits. The diameters of these maculae are rarely very large, but in certain species (for example, Ciona), they are unusually small. In some tissues, notably those of Diplosoma and Botryllus, they are all of rather similar size, but very numerous. In yet others, such as Molgula, they are polygonal with angular outlines, as might be indicative of the uncoupled state. In many attributes, these various junctions are more similar to those found in the tissues of vertebrates, than to those in the invertebrates, which the adult zooid forms of these lowly chordates resemble anatomically.

The application of freeze-fracture in the analysis of intercellular junctions in pleuro-pulmonary tumors

1990 ◽  
Vol 48 (3) ◽  
pp. 540-541
Author(s):  
T. M. Mukherjee ◽  
J. G. Swift
Keyword(s):  
Gap Junctions ◽  
Tight Junctions ◽  
Thin Section ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Squamous Cell Carcinomas ◽  
Cell Junctions ◽  
Thin Sections ◽  
Pulmonary Tumors ◽  
Diagnostic Importance

Thin section and freeze-fracture techniques have been used to examine the morphology of cell junctions in a variety of pleuro-pulmonary tumours with the aim of identifying features that may be of diagnostic importance or of significance in the development of the tumour. Freeze-fracture preparations are particularly useful for the analysis of cell junctions, since extensive face views of the interior of the cell membrane are exposed. This enables precise characterisation of the type of junctions present, their extent and their inter-relationships.Freeze-fracture replicas can reveal the presence of junctions that would be difficult or impossible to detect in thin sections. For example, desmosomes are a well-known feature in thin sections of squamous cell carcinomas, but these tumours may also have focal tight junctions and gap junctions (Figs. 1,2). The tight and gap junctions can occur separately (Fig.l), or in combination (Fig. 2). Similarly, in a recent study of a case of “Ewing’s sarcoma”, replicas showed the presence of unusual, elaborate focal tight junctions, a feature never suspected from the routine thin section studies of this tumour.

Flounder intestinal absorptive cells have abundant gap junctions and may be coupled

1984 ◽  
Vol 246 (1) ◽  
pp. C77-C83 ◽  
Author(s):  
R. L. Curtis ◽  
J. S. Trier ◽  
R. A. Frizzell ◽  
N. M. Lindem ◽  
J. L. Madara
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Intestinal Epithelium ◽  
Winter Flounder ◽  
Potential Difference ◽  
Intestinal Cell ◽  
Intramembrane Particles ◽  
Absorptive Cells ◽  
Small Intestinal ◽  
Apical Membranes

We noted that, unlike mammalian intestinal absorptive cells, cells of the winter flounder (Pseudopleuronectes americanus) displayed abundant gap junctions on the lateral plasma membrane. We compared the distribution of gap junctions in winter flounder to that in rabbit intestinal epithelium. We also examined for evidence of gap junction-mediated intercellular coupling by comparing the cell-to-cell variation of electrical potential difference across winter flounder intestinal cell apical membranes with that in rabbit small intestinal epithelium in which gap junctions are rare. Gap junctions were seen in 95% of flounder absorptive cells and were localized largely to the apical third of the lateral membrane. Individual gap junctions often contained several hundred uniform 9-nm intramembrane particles. Gap junction size and structure was independent of the position of individual absorptive cells on mucosal folds. These findings sharply contrasted flounder intestinal absorptive cells with rabbit small intestinal absorptive cells, in which gap junctions were rarely detected and when present consisted of few intramembrane particles. Correlating with this distribution of morphologically detectable gap junctions, rabbit small intestinal epithelial cells demonstrated marked variability in potential difference across their apical membranes, whereas those in flounder small intestine showed little variation in apical membrane potential difference. Thus, in contrast to intestinal epithelium of rabbits, flounder intestinal epithelium demonstrates morphological and functional characteristics, suggesting a substantial degree of electrical coupling.

A New Junctional Structure in the Epithelia of Insects of the Order Dictyoptera

1972 ◽  
Vol 10 (3) ◽  
pp. 683-691
Author(s):  
N. E. FLOWER
Keyword(s):  
Epithelial Cells ◽  
Gap Junctions ◽  
Gap Junction ◽  
Tight Junctions ◽  
Hexagonal Array ◽  
Septate Junctions ◽  
New Type ◽  
Junctional Complexes ◽  
Junctional Structure

The junctional complexes in the epithelia of insects of the order Dictyoptera have been investigated using the freeze-etch technique. As well as septate junctions, a new type of junction has been identified and the name ‘inverted gap junction’ proposed. The patch-like distribution of the inverted gap junctions basal to and often closely associated with septate junctions is very similar to the form of gap junctions and their relationship to tight junctions in vertebrates. This suggests that the inverted gap junctions, like normal gap junctions, could perform a communicating function between epithelial cells. The following features distinguish inverted gap junctions from normal gap junctions in freeze-etch preparations: (i) the arrays of particles and holes within inverted gap junctions appear on B- and A-type faces respectively, i.e. on the opposite faces to the particles and holes in gap junctions; (ii) the particles within inverted gap junctions appear to lie in rows which anastomose to form an irregular net, and not in an hexagonal array, as occurs in gap junctions.

scholarly journals Unusual structural features and assembly of gap and pleated septate junctions in embryonic cockroach CNS

1985 ◽  
Vol 76 (1) ◽  
pp. 269-281
Author(s):  
L.S. Swales ◽  
N.J. Lane
Keyword(s):  
Gap Junctions ◽  
Tight Junctions ◽  
Glial Cell ◽  
Structural Features ◽  
Septate Junctions ◽  
Intramembrane Particles ◽  
Cell Processes ◽  
Gap Junctional ◽  
Perineurial Cells

Junctional assembly in the developing CNS in cockroach embryos has been studied during the last half of neurogenesis. Atypical linear tracts of gap junctions are found to develop between attenuated cytoplasmic glial cell processes and their overlying perineurial cells during the last third of development. During both perineurial and glial gap-junctional formation, 13 nm E face (EF) intramembrane particles (IMPs), such as are characteristic of arthropod gap junctions, are seen initially as free IMPs; these then become arranged in loose irregular clusters or alignments and finally are aggregated in plaques. P face ridges (or EF grooves), typical of tight junctions, are found on the same perineurial membrane face as assembling gap-junctional PF pits (or EF particles). Pleated separate junctions also develop between adjacent perineurial processes during the last third of embryogenesis; these form by the apparent migration of individual 8 nm PF IMPs into meandering rows, which then become aligned in numerous orderly parallel stacks. Although all these junctions occur on the same perineurial membrane face, the IMPs that form the different junctional types never appear to be confused during junctional assembly. The cues to signal the advent of these precise patterns, however, are unknown.

scholarly journals Two Drosophila Innexins Are Expressed in Overlapping Domains and Cooperate to Form Gap-Junction Channels

2000 ◽  
Vol 11 (7) ◽  
pp. 2459-2470 ◽  
Author(s):  
Lucy A. Stebbings ◽  
Martin G. Todman ◽  
Pauline Phelan ◽  
Jonathan P. Bacon ◽  
Jane A. Davies
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Ectopic Expression ◽  
In Vivo Studies ◽  
Electrophysiological Properties ◽  
Gap Junction Channels ◽  
Overlapping Domains ◽  
In Vitro Data

Members of the innexin protein family are structural components of invertebrate gap junctions and are analogous to vertebrate connexins. Here we investigate two Drosophila innexin genes,Dm-inx2 and Dm-inx3 and show that they are expressed in overlapping domains throughout embryogenesis, most notably in epidermal cells bordering each segment. We also explore the gap-junction–forming capabilities of the encoded proteins. In pairedXenopus oocytes, the injection of Dm-inx2mRNA results in the formation of voltage-sensitive channels in only ∼ 40% of cell pairs. In contrast, Dm-Inx3 never forms channels. Crucially, when both mRNAs are coexpressed, functional channels are formed reliably, and the electrophysiological properties of these channels distinguish them from those formed by Dm-Inx2 alone. We relate these in vitro data to in vivo studies. Ectopic expression ofDm-inx2 in vivo has limited effects on the viability ofDrosophila, and animals ectopically expressingDm-inx3 are unaffected. However, ectopic expression of both transcripts together severely reduces viability, presumably because of the formation of inappropriate gap junctions. We conclude that Dm-Inx2 and Dm-Inx3, which are expressed in overlapping domains during embryogenesis, can form oligomeric gap-junction channels.

Freeze-fracture studies of frog atrial fibres

1976 ◽  
Vol 22 (2) ◽  
pp. 427-434
Author(s):  
F. Mazet ◽  
J. Cartaud
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Outer Membrane ◽  
Electrical Coupling ◽  
Freeze Fracture ◽  
Present Knowledge ◽  
Inner Membrane ◽  
Freeze Fracturing ◽  
Morphological Variant ◽  
Characteristic Features

The freeze-fracturing technique was used to characterize the junctional devices involved in the electrical coupling of frog atrial fibres. These fibres are connected by a type of junction which can be interpreted as a morphological variant of the “gap junction” or “nexus”. The most characteristic features are rows of 9-nm junctional particles forming single or anastomosed circular profiles on the inner membrane face, and corresponding pits on the outer membrane face. Very seldom aggregates consisting of few geometrically disposed 9-nm particles are found. The significance of the junctional structures in the atrial fibres is discussed, with respect to present knowledge about junctional features of gap junctions in various tissues, including embryonic ones.

Investigation of the roles of Ca2+ and InsP3 diffusion in the coordination of Ca2+ signals between connected hepatocytes

2001 ◽  
Vol 114 (11) ◽  
pp. 1999-2007
Author(s):  
Caroline Clair ◽  
Cécile Chalumeau ◽  
Thierry Tordjmann ◽  
Josiane Poggioli ◽  
Christophe Erneux ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Significant Role ◽  
Signaling Molecules ◽  
Rat Hepatocyte ◽  
Inositol 1,4,5 Trisphosphate ◽  
Gap Junction Coupling ◽  
Junction Coupling ◽  
Insp3 Receptor

Glycogenolytic agonists induce coordinated Ca2+ oscillations in multicellular rat hepatocyte systems as well as in the intact liver. The coordination of intercellular Ca2+ signals requires functional gap-junction coupling. The mechanisms ensuring this coordination are not precisely known. We investigated possible roles of Ca2+ or inositol 1,4,5-trisphosphate (InsP3) as a coordinating messengers for Ca2+ spiking among connected hepatocytes. Application of ionomycin or of supra-maximal concentrations of agonists show that Ca2+ does not significantly diffuse between connected hepatocytes, although gap junctions ensure the passage of small signaling molecules, as demonstrated by FRAP experiments. By contrast, coordination of Ca2+ spiking among connected hepatocytes can be favored by a rise in the level of InsP3, via the increase of agonist concentrations, or by a shift in the affinity of InsP3 receptor for InsP3. In the same line, coordination cannot be achieved if the InsP3 is rapidly metabolized by InsP3-phosphatase in one cell of the multiplet. These results demonstrate that even if small amounts of Ca2+ diffuse across gap junctions, they most probably do not play a significant role in inducing a coordinated Ca2+ signal among connected hepatocytes. By contrast, coordination of Ca2+ oscillations is fully dependent on the diffusion of InsP3 between neighboring cells.

scholarly journals In vivo assembly of tight junctions in fetal rat liver.

1975 ◽  
Vol 67 (2) ◽  
pp. 310-319 ◽  
Author(s):  
R Montesano ◽  
D S Friend ◽  
A Perrelet ◽  
L Orci
Keyword(s):  
Tight Junctions ◽  
De Novo ◽  
Early Stage ◽  
Fetal Life ◽  
Bile Canaliculi ◽  
Linear Arrays ◽  
Fetal Rat ◽  
Particle Aggregates ◽  
Fetal Rat Liver

Examination of glutaraldehyde-fixed, freeze-fractured livers from 14-15-day rat fetuses provided the basis for the following observations. Membrane particles align in otherwise poorly particulated areas of the presumptive pericanalicular plasma membrane (A face), frequently forming a discontinuous "honey-comb" network joining small particle islands. Even at this early stage, contiguous B-fracture faces contain furrows, rather than rows of pits, distinguishing the linear particle aggregates on the A face as developing tight junctions rather than gap junctions. Short segments of these linear arrays merge with smooth ridges clearly identifiable as segments of discontinuous tight junctions. With the continuing confluence of particulate and smooth ridge segments, mature tight junctions become fully appreciable. We conclude that tight junctions form de novo by the alignment and fusion of separate particles into beaded ridges which, in turn, become confluent and are transformed into continuous smooth ones. At 21 days of fetal life, most of the images of assembly have disappeared, and the liver reveals well-formed bile canaliculi sealed by mature tight junctions.

scholarly journals Gap junction structures after experimental alteration of junctional channel conductance.

1985 ◽  
Vol 101 (5) ◽  
pp. 1741-1748 ◽  
Author(s):  
T M Miller ◽  
D A Goodenough
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Electron Micrographs ◽  
Time Course ◽  
Structural Changes ◽  
Lucifer Yellow ◽  
Freeze Fracture ◽  
Channel Conductance ◽  
Experimental Alteration ◽  
Quick Freezing

Gap junctions are known to present a variety of different morphologies in electron micrographs and x-ray diffraction patterns. This variation in structure is not only seen between gap junctions in different tissues and organisms, but also within a given tissue. In an attempt to understand the physiological meaning of some aspects of this variability, gap junction structure was studied following experimental manipulation of junctional channel conductance. Both physiological and morphological experiments were performed on gap junctions joining stage 20-23 chick embryo lens epithelial cells. Channel conductance was experimentally altered by using five different experimental manipulations, and assayed for conductance changes by observing the intercellular diffusion of Lucifer Yellow CH. All structural measurements were made on electron micrographs of freeze-fracture replicas after quick-freezing of specimens from the living state; for comparison, aldehyde-fixed specimens were measured as well. Analysis of the data generated as a result of this study revealed no common statistically significant changes in the intrajunctional packing of connexons in the membrane plane as a result of experimental alteration of junctional channel conductance, although some of the experimental manipulations used to alter junctional conductance did produce significant structural changes. Aldehyde fixation caused a dramatic condensation of connexon packing, a result not observed with any of the five experimental uncoupling conditions over the 40-min time course of the experiments.

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