scholarly journals ASSEMBLY OF GAP JUNCTIONS DURING AMPHIBIAN NEURULATION

1974 ◽  
Vol 62 (1) ◽  
pp. 32-47 ◽  
Author(s):  
Robert S. Decker ◽  
Daniel S. Friend
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Ruthenium Red ◽  
Junctional Complex ◽  
Translational Movement ◽  
Pile Up ◽  
Neuroepithelial Cells ◽  
Solitary Domains ◽  
Number Of Particles

Sequential thin-section, tracer (K-pyroantimonate, lanthanum, ruthenium red, and horseradish peroxidase), and freeze-fracture studies were conducted on embryos and larvae of Rana pipiens to determine the steps involved in gap junction assembly during neurulation. The zonulae occludentes, which join contiguous neuroepithelial cells, fragment into solitary domains as the neural groove deepens. These plaque-like contacts also become permeable to a variety of tracers at this juncture. Where the ridges of these domains intersect, numerous 85-Å participles apparently pile up against tight junctional remnants, creating arrays recognizable as gap junctions. With neural fold closure, the remaining tight junctional elements disappear and are replaced by macular gap junctions. Well below the junctional complex, gap junctions form independent of any visible, preexisting structure. Small, variegated clusters, containing 4–30 particles located in flat, particle-free regions, characterize this area. The number of particles within these arrays increases and they subsequently blend together into a polygonally packed aggregate resembling a gap junction. The assembly process in both apical and basal regions conforms with the concept of translational movement of particles within a fluid plasma membrane.

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.

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.

Heart gap junction preparations reveal hemiplaques by atomic force microscopy

1995 ◽  
Vol 268 (4) ◽  
pp. C968-C977 ◽  
Author(s):  
R. Lal ◽  
S. A. John ◽  
D. W. Laird ◽  
M. F. Arnsdorf
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Long Range ◽  
Connexin 43 ◽  
Plasma Membranes ◽  
Aqueous Media ◽  
Freeze Fracture ◽  
Isolated Rat Heart ◽  
Hexagonal Packing ◽  
Atomic Force

Current structural models of gap junctions indicate two apposed plasma membranes with hexagonally packed hemichannels in each membrane aligning end to end. These channels connect the cytoplasms of contacting cells. Images of isolated rat heart gap junctions have been made with the atomic force microscope in aqueous media. We show that native cardiac gap junctions have a thickness of 25 +/- 0.6 nm. This decreases to 17 nm when they are treated with trypsin, which is known to remove some cytoplasmic components of connexin 43. Imaging shows subunits with a center to center spacing of approximately 9-10 nm and long range hexagonal packing, measurements in agreement with studies using freeze-fracture and negative-stain electron microscopy. In addition to gap junctions, we imaged structures that had all the characteristics of native gap junctions except their thickness was limited to 9-11 nm. They also show long range hexagonal packing and center to center spacing of 9-10 nm. These structures decrease in thickness, to 6-9 nm, when treated with trypsin. We have called these structures hemiplaques. They appear to be present endogenously in the preparation, as we have ruled out their being an artifact of imaging by AFM. However, it remains to be determined if they are a consequence of the procedure used in isolating gap junctions or a possible intermediary in gap junction formation.

scholarly journals VARIATIONS IN TIGHT AND GAP JUNCTIONS IN MAMMALIAN TISSUES

1972 ◽  
Vol 53 (3) ◽  
pp. 758-776 ◽  
Author(s):  
Daniel S. Friend ◽  
Norton B. Gilula
Keyword(s):  
Smooth Muscle ◽  
Gap Junctions ◽  
Tight Junctions ◽  
Adrenal Cortex ◽  
Freeze Fracture ◽  
Junctional Complex ◽  
Exocrine Glands ◽  
Rat Pancreas ◽  
Zonula Occludens ◽  
Mammalian Tissues

The fine structure and distribution of tight (zonula occludens) and gap junctions in epithelia of the rat pancreas, liver, adrenal cortex, epididymis, and duodenum, and in smooth muscle were examined in paraformaldehyde-glutaraldehyde-fixed, tracer-permeated (K-pyroantimonate and lanthanum), and freeze-fractured tissue preparations. While many pentalaminar and septilaminar foci seen in thin-section and tracer preparations can be recognized as corresponding to well-characterized freeze-fracture images of tight and gap junction membrane modifications, many others cannot be unequivocally categorized—nor can all freeze-etched aggregates of membrane particles. Generally, epithelia of exocrine glands (pancreas and liver) have moderate-sized tight junctions and large gap junctions, with many of their gap junctions basal to the junctional complex. In contrast, the adrenal cortex, a ductless gland, may not have a tight junction but does possess large gap junctions. Mucosal epithelia (epididymis and intestine) have extensive tight junctions, but their gap junctions are not as well developed as those of glandular tissue. Smooth muscle contains numerous small gap junctions The incidence, size, and configuration of the junctions we observed correlate well with the known functions of the junctions and of the tissues where they are found.

The syneretic lens junction

1984 ◽  
Vol 42 ◽  
pp. 16-19
Author(s):  
J. David Robertson ◽  
M.J. Costello ◽  
T.J. McIntosh
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Cell Membranes ◽  
Freeze Fracture ◽  
Enzymatic Digestion ◽  
Fiber Cell ◽  
Intermembrane Space ◽  
Minor Components ◽  
Thin Sections ◽  
Fiber Cells

The lens of the eye consists of closely adherent greatly elongated flattened narrow fiber cells that are electrically coupled by gap junctions. In thin sections the 100-150 Å intermembrane space usually seen in tissues between adjacent cells is greatly reduced between adjacent fiber cells. Freeze-fracture-etch (FFE) studies have demonstrated gap junctions between fiber cells. Several workers have observed expanses of square crystallinity in fiber cell membranes with a lattice constant of 6-7 nm. This has usually been attributed variously to artifact induced by calcium, pH or proteolytic enzymatic digestion. Square arrays have been seen in isolated fractions of fiber cell membranes prepared with detergents as minor components and dismissed as relatively insignificant and either related or unrelated to gap junctions. Some have regarded them as a form of gap junction.

Intercellular communication between epithelial and fiber cells of the eye lens

1994 ◽  
Vol 107 (4) ◽  
pp. 799-811 ◽  
Author(s):  
S. Bassnett ◽  
J.R. Kuszak ◽  
L. Reinisch ◽  
H.G. Brown ◽  
D.C. Beebe
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Cell Types ◽  
Lens Epithelium ◽  
Fiber Cell ◽  
Fracture Plane ◽  
Metabolic Cooperation ◽  
Fiber Cells ◽  
Resistance Pathway

Results of electrical, dye-coupling and morphological studies have previously suggested that gap junctions mediate communication between the anterior epithelium of the lens and the underlying lens fiber cells. This connection is believed to permit ‘metabolic cooperation’ between these dissimilar cell types and may be of particular importance to the fiber cells, which are thought incapable of autonomous ionic homeostasis. We reinvestigated the nature of the connection between epithelial and fiber cells of the embryonic chicken lens using fluorescence confocal microscopy and freeze-fracture analysis. In contrast to earlier studies, our data provided no support for gap-junction-mediated transport from the lens epithelium to the fibers. Fluorescent dyes loaded biochemically into the lens epithelium were retained there for more than one hour. There was a decrease in epithelial fluorescence over this period, but this was not accompanied by an increase in fiber cell fluorescence. Diffusional modeling suggested that these data were inconsistent with the presence of extensive epithelium-fiber cell coupling, even if the observed decrease in epithelial fluorescence was attributed exclusively to the diffusion of dye into the fiber mass via gap junctions. Furthermore, the rate of loss of fluorescence from isolated epithelia was indistinguishable from that measured in whole lenses, suggesting that decreased epithelial fluorescence resulted from photobleaching and leakage of dye rather than diffusion, via gap junctions, into the fibers. Analysis of freeze-fracture replicas of plasma membranes at the epithelial-fiber cell interface failed to reveal evidence of gap-junction plaques, although evidence of endocytosis was abundant. These studies were done under conditions where the location of the fracture plane was unambiguous and where gap junctions could be observed in the lateral membranes of neighboring epithelial and fiber cells. Paradoxically, tracer molecules injected into the fiber mass were able to pass into the epithelium via a pathway that was not blocked by incubation at 4 degrees C or by treatment with octanol and which excluded large (approximately 10 kDa) molecular mass tracers. Together with previous measurements of electrical coupling between fiber cells and epithelial cells, these data indicate the presence of a low-resistance pathway connecting these cell types that is not mediated by classical gap junctions.

Plasma membranes, cell junctions and cuticle of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea

1983 ◽  
Vol 59 (1) ◽  
pp. 159-182
Author(s):  
J. Kukulies ◽  
H. Komnick
Keyword(s):  
Gap Junctions ◽  
Structural Control ◽  
Plasma Membranes ◽  
Freeze Fracture ◽  
Septate Junction ◽  
Cell Junctions ◽  
Junctional Complex ◽  
Apical Region ◽  
Thin Sections ◽  
Aeshna Cyanea

The cell membranes and cell junctions of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea were examined in thin sections and by freeze-fracture. These epithelia function in active ion absorption and maintain a high concentration gradient between the haemolymph and the fresh-water environment. Freeze-fracturing reveals fine-structural differences in the intramembraneous particles of the luminal and contraluminal plasma membranes of these epithelia, reflecting the functional diversity of the two membranes, which are separated by the junctional complex. The particle frequency of the basolateral plasma membranes is reduced after transfer of the larvae into high concentrations of environmental salinity. The junctional complex is located in the apical region and composed of three types of cell junctions: the zonula adhaerens, seen in freeze-fracture as a nearly particle-free zone; the extended and highly convoluted pleated septate junction and randomly interspersed gap junctions of the inverted type. Gap junctions also occur between the basolateral plasma membranes. They provide short-cuts in the diffusion pathway for direct and rapid co-ordination of the interconnected cell processes. Colloidal and ionic lanthanum tracer solutions applied in vivo from the luminal side penetrate through the cuticle via epicuticular depressions, but invade only the apical portion of the junctional complex. This indicates that the pleated septate junction constitutes a structural control of the paracellular pathway across the chloride epithelia, which are devoid of tight junctions. The structure of the pleated septate junctions is interpreted as a device for the extension of the diffusion distance, which is inversely related to the net diffusion. A conservative estimate of the total length of the junction, and the number and extension of septa reveals that the paracellular route exceeds the transcellular route by a factor of 50.

Synthesis and assembly of human beta 1 gap junctions in BHK cells by DNA transfection with the human beta 1 cDNA

1995 ◽  
Vol 108 (12) ◽  
pp. 3725-3734 ◽  
Author(s):  
N.M. Kumar ◽  
D.S. Friend ◽  
N.B. Gilula
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Growth Control ◽  
Double Membrane ◽  
Correct Orientation ◽  
Junctional Communication ◽  
Junction Protein ◽  
Particle Aggregates ◽  
Metallothionein Promoter

Gap junctional communication is important in many physiological processes, including growth control, patterning, and the synchronization of cell-to-cell activities. It has been difficult to study the synthesis and assembly of gap junctions due to their low abundance. To overcome this limitation, baby hamster kidney cells (BHK) have been transfected with a human beta 1 (Cx32) connexin cDNA construct. Expression was placed under the control of the mouse metallothionein promoter that can be induced by heavy metals. The transfected cells were characterized by DNA, RNA and protein analysis, as well as by scrape loading to detect functional channels. Functional beta 1 connexin was detected only in cells transfected with beta 1 connexin cDNA in the correct orientation (beta 1-BHK). Analysis of the cells by light microscopic immunocytochemistry indicated that beta 1 connexin antigen was localized to the plasma membrane and to several intracellular compartments. Characterization with thin section electron microscopy revealed extensive areas of assembled double membrane gap junctions between cells (on the cell surface), in the endoplasmic reticulum (ER), and the nuclear envelope. This unusual intracellular distribution for assembled gap junction protein was confirmed by freeze fracture analysis, which revealed large particle aggregates, characteristic of gap junction plaques, on the fracture faces of all these membranes. The presence of gap junction particle aggregates in the ER suggests that the oligomerization of connexin can occur at its site of synthesis. Further, the process of assembly into double membrane junction structures in intracellular membranes may be driven by connexin protein concentration.

scholarly journals Cardiac gap junction configuration after an uncoupling treatment as a function of time.

1979 ◽  
Vol 82 (1) ◽  
pp. 66-75 ◽  
Author(s):  
K M Baldwin
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Homogeneous Structure ◽  
Electrical Uncoupling ◽  
Gap Junctional ◽  
Injury Control ◽  
Junction Structure ◽  
Rabbit Atrium

Rabbit ventricle either was fixed in glutaraldehyde without injury (control) or was injured before fixation, presumably causing electrical uncoupling of the gap junctions. All tissue was then processed for freeze-fracture. Replicas of control gap junctions exhibited irregular packing of the P-face particles and E-face pits. Average center-to-center spacing of the particles was 10.5 nm. Tissue fixed 1-5 min after injury showed clumping of gap junctional particles and pits. Within the clumps, the particles and pits were hexagonally packed and the center-to-center spacing of the particles averaged 9.5 nm. In tissue fixed 15-30 min after injury, the clumps of gap junctional particles had coalesced into a homogeneous structure in most junctions. The packing of the particles and pits was hexagonal and the spacing of the particles averaged 9.5 nm. A few pieces of rabbit atrium were frozen without prior fixation or cryoprotection to try to assess the effect of glutarldehyde fixation on gap junction structure. In this tissue the gap junctional particles were irregularly packed and their spacing averaged 10.0 nm.

scholarly journals Hormonal modulation of ovarian interstitial cells with particular reference to gap junctions.

1979 ◽  
Vol 81 (1) ◽  
pp. 104-114 ◽  
Author(s):  
R C Burghardt ◽  
E Anderson
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Cell Morphology ◽  
Interstitial Cell ◽  
Freeze Fracture ◽  
Interstitial Cells ◽  
Chorionic Gonadotrophin ◽  
Human Chorionic Gonadotrophin ◽  
Hormonal Modulation ◽  
Pituitary Ablation

Thin-section and freeze-fracture studies on the rat ovarian interstitial cells revealed reductions in the size and the number of gap junctions after pituitary ablation. Small gap junctions, however, persist as long as 90 days after hypophysectomy even though regressive cytoplasmic changes are completed 75 d earlier. Administration of exogenous human chorionic gonadotrophin (HCG) results in the restoration of the normal interstitial cell morphology which is accompanied by amplification of junctional membrane. Within 24 h of hormone application, gap junction growth is characterized by the appearance of formation plaques. These studies suggest that the effect of hormone on interstitial cell gap junctions is to modulate the junctional surface area.

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