scholarly journals COEXISTENCE OF GAP AND SEPTATE JUNCTIONS IN AN INVERTEBRATE EPITHELIUM

1971 ◽  
Vol 50 (1) ◽  
pp. 92-101 ◽  
Author(s):  
A. J. Hudspeth ◽  
J. P. Revel
Keyword(s):  
Electron Microscope ◽  
Gap Junctions ◽  
Gap Junction ◽  
Extracellular Space ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
High Electron ◽  
Septate Junctions ◽  
Electrotonic Coupling ◽  
Lanthanum Tracer

The intercellular junctions of the epithelium lining the hepatic caecum of Daphnia were examined. Electron microscope investigations involved both conventionally fixed material and tissue exposed to a lanthanum tracer of the extracellular space. Both septate junctions and gap junctions occur between the cells studied. The septate junctions lie apically and resemble those commonly discerned between cells of other invertebrates. They are atypical in that the high electron opacity of the extracellular space obscures septa in routine preparations. The gap junctions are characterized by a uniform 30 A space between apposed cell membranes. Lanthanum treatment of gap junctions reveals an array of particles of 95 A diameter and 120 A separation lying in the plane of the junction. As this pattern closely resembles that described previously in vertebrates, it appears that the gap junction is phylogenetically widespread. In view of evidence that the gap junction mediates intercellular electrotonic coupling, the assignment of a coupling role to other junctions, notably the septate junction, must be questioned wherever these junctions coexist.

Phylogenetic Relationships within Theinvertebrata in Relation to Thestructure of Septate Junctions and the development of ‘Occluding’ Junctional Types

1982 ◽  
Vol 53 (1) ◽  
pp. 279-305 ◽  
Author(s):  
COLIN R. GREEN ◽  
PATRICIA R. BERGQUIST
Keyword(s):  
Tight Junction ◽  
Phylogenetic Relationships ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
Simple Type ◽  
Septate Junctions ◽  
Exterior Surface ◽  
Lanthanum Tracer ◽  
To Come

The structures of 13 variants of invertebrate septate junction are reviewed on the basis offreeze-fracture, lanthanum tracer and thin-section studies. In addition, a simple type ofoccluding junction in the phylum Porifera, a variation of tight junction in the phylum Tunicateand the vertebrate tight junction are covered. All the junctions considered form a belt around the apical circumference of cells lining a lumen or an exterior surface. The large number of these junctions now recognized permits discussion relating to invertebrate classification and suggested phylogenetic relationships, and to the development of intercellular junctions. The relationships revealed are discussed under three headings: Coelenterates and lower invertebrates, Proterostomia (the annelid, molluscan and arthropod lineage) and the Deuterostomia(the echinoderm and chordate lineage). It is proposed that the pleated septate junction of the lower invertebrates resembles that of the hydrozoan rather than anthozoan Coelenterates. This lower invertebrate pleated septate junction occurs in several lower invertebrate phyla including the Annelida (of the proterostome lineage), but also occurs in the Sipunculoidea, a group supposedly on the deuterostome lineage.The proterostome line includes the molluscs and the arthropods, which have the molluscarthropodpleated septate junction. Several variations of the smooth septate junction are alsoseen in Arthropoda. Among the deuterostomes the Chaetognatha have both a paired septatejunction and a pleated junction and are therefore considered to be not very far removed fromthe Sipunculoidea. The echinoderms and hemichordates also have double-septum septatejunctions. In addition however, these two phyla have anastomosing septate junctions thatare very similar, varying only in their final configuration. Of the two, the echinoderm anastomosingseptate junction most closely resembles the tight junction seen in the tunicates, and the Hemichordata are therefore considered to be a lateral development from the main lineof chordate evolution. The tunicates have a tight junction similar to that seen in vertebrates;it is however more ‘leaky’ and has distinctive freeze-fracture characteristics.In the phylum Porifera a form of simple parallel membrane junction appears to serve anoccluding function. This junction has regular intercellular spacing in the absence of any septaand it is suggested that the spacing in septate junctions is probably not dictated by the septa.This interpretation is reasonable particularly when the diversity of septal types in conjunctionwith stable intercellular spacing is considered. Finally, a theory is put forward suggesting thatin evolution a change from the septate to the tight junction could simply involve a modificationof a ‘membrane spacing factor’, which allows the membranes of adjacent cells to come together at intervals, in the normal tight junction pattern.

Isolation and characterization of invertebrate smooth septate junctions

1983 ◽  
Vol 62 (1) ◽  
pp. 351-370
Author(s):  
C.R. Green ◽  
C. Noirot-Timothee ◽  
C. Noirot
Keyword(s):  
Molecular Weight ◽  
Gap Junctions ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
Major Protein ◽  
Septate Junctions ◽  
Isolation And Characterization ◽  
Significant Difference ◽  
Freeze Fracture Electron Microscopy

Using modifications of techniques used for the isolation of macula type intercellular junctions (gap junctions and desmosomes) the arthropod smooth septate junction has been isolated from insect midgut tissue. Midguts from cockroaches or mealworms were used and membrane fractions were obtained by sucrose gradient and ultracentrifugation techniques. Preparations with reasonable concentrations of septate junction were obtained and have been studied by thin-section, negative-stain and freeze-fracture electron microscopy. The junctions appeared to be well preserved, although there was evidence that the junction strands were able to slide within the plane of the membrane. Septa were seen to have a cross-striated appearance when viewed after negative staining but their exact structure remained difficult to determine. Polyacrylamide gel electrophoretic studies demonstrated the reproducibility of the isolation procedure and showed that septa may have a 47 000 molecular weight glycoprotein component. Gel electrophoresis also gave some indication of the intramembrane biochemistry of the smooth septate junction, with proteins of 31 000 and 32 000 molecular weight always occurring in the junction fractions. The junctions were, however, very sensitive to both mechanical and chemical treatments, the septa were destroyed by rough homogenization or by treatment with urea at a concentration as low as 1 M. Freeze-fracture of untreated, isolated junctions demonstrated no differences from junctions in intact tissue, while replicas of urea-treated material were more difficult to interpret as the component parts of the junctions became separated once the septa had been destroyed. Gap junctions were also obtained and resisted both mechanical and chemical treatment, which destroyed the septate junctions. Their major protein component appeared to have a molecular weight of 36 000. Attempts to isolate pleated septate junctions (from insects, molluscs and annelids) by the same techniques failed, implying a significant difference in the structures of the two types of septate junction.

scholarly journals A freeze-fracture and lanthanum tracer study of the complex junction between Sertoli cells of the canine testis.

1978 ◽  
Vol 76 (1) ◽  
pp. 57-75 ◽  
Author(s):  
C J Connell
Keyword(s):  
Tight Junctions ◽  
Sertoli Cells ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
Septate Junctions ◽  
Thin Sections ◽  
En Face ◽  
Lanthanum Tracer ◽  
Complex Junction

What appear to be true septate junctions by all techniques currently available for the cytological identification of intercellular junctions are part of a complex junction that interconnects the Sertoli cells of the canine testis. In the seminiferous epithelium, septate junctions are located basal to belts of tight junctions. In thin sections, septate junctions appear as double, parallel, transverse connections or septa spanning an approximately 90-A intercellular space between adjacent Sertoli cells. In en face sections of lanthanum-aldehyde-perfused specimens, the septa themselves exclude lanthanum and appear as electron-lucent lines arranged in a series of double, parallel rows on a background of electron-dense lanthanum. In freeze-fracture replicas this vertebrate septate junction appears as double, parallel rows of individual or fused particles which conform to the distribution of the intercellular septa. Septate junctions can be clearly distinguished from tight junctions as tight junctions prevent the movement of lanthanum tracer toward the lumen, appear as single rows of individual or fused particles in interlacing patterns within freeze-fracture replicas, and are seen as areas of close membrane apposition in thin sections. Both the septate junction and the tight junction are associated with specializations of the Sertoli cell cytoplasm. This is the first demonstration in a vertebrate tissue of a true septate junction.

Dissociation of lens fibre gap junctions releases MP70

1988 ◽  
Vol 91 (3) ◽  
pp. 415-421 ◽  
Author(s):  
J. Kistler ◽  
S. Bullivant
Keyword(s):  
Electron Microscope ◽  
Gap Junctions ◽  
Gap Junction ◽  
Plasma Membranes ◽  
Gradient Centrifugation ◽  
Membrane Structures ◽  
Treatment Results ◽  
Double Membrane ◽  
Lens Fibre ◽  
Junction Proteins

MIP and MP70 are putative gap junction components in the plasma membranes of the mammalian lens fibre cells. We show now that MP70 can be solubilized separately from MIP in mild detergent solutions, and that this treatment results in the dissociation of the fibre gap junctions. Solubilized MP70 was isolated as 16.9 S particles by velocity gradient centrifugation and in the electron microscope had the appearance of short double-membrane structures consistent with connexon-pairs. These observations open a new experimental avenue in which to characterize separately the two putative lens gap junction proteins structurally and functionally.

Effects of diminished expression of connexin43 on gap junction number and size in ventricular myocardium

2000 ◽  
Vol 278 (5) ◽  
pp. H1662-H1670 ◽  
Author(s):  
Jeffrey E. Saffitz ◽  
Karen G. Green ◽  
William J. Kraft ◽  
Kenneth B. Schechtman ◽  
Kathryn A. Yamada
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Ventricular Myocytes ◽  
Intercellular Junctions ◽  
Ventricular Myocardium ◽  
Electron Microscopic ◽  
Confocal Immunofluorescence Microscopy ◽  
Normal Number ◽  
Gap Junction Channel ◽  
Junction Protein

Gap junction number and size vary widely in cardiac tissues with disparate conduction properties. Little is known about how tissue-specific patterns of intercellular junctions are established and regulated. To elucidate the relationship between gap junction channel protein expression and the structure of gap junctions, we analyzed Cx43 +/− mice, which have a genetic deficiency in expression of the major ventricular gap junction protein, connexin43 (Cx43). Quantitative confocal immunofluorescence microscopy revealed that diminished Cx43 signal in Cx43 +/− mice was due almost entirely to a reduction in the number of individual gap junctions (226 ± 52 vs. 150 ± 32 individual gap junctions/field in Cx43 +/+ and +/− ventricles, respectively; P < 0.05). The mean size of an individual gap junction was the same in both groups. Immunofluorescence results were confirmed with electron microscopic morphometry. Thus when connexin expression is diminished, ventricular myocytes become interconnected by a reduced number of large, normally sized gap junctions, rather than a normal number of smaller junctions. Maintenance of large gap junctions may be an adaptive response supporting safe ventricular conduction.

scholarly journals On gap junction structure.

1980 ◽  
Vol 86 (1) ◽  
pp. 190-198 ◽  
Author(s):  
G Zampighi ◽  
J M Corless ◽  
J D Robertson
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Rat Liver ◽  
Extracellular Space ◽  
Plasma Membranes ◽  
Negative Staining ◽  
The Other ◽  
Central Axis ◽  
Thin Sectioning ◽  
Junction Structure

We have studied the stain distribution within rat liver gap junctions for specimens prepared by thin sectioning and negative staining. Pools of stain molecules exist in two specific locations with respect to the distinctive morphological units (connexons) of the junction. One pool of stain surrounds the connexons and is restricted to the extracellular space in the gap between the adjacent plasma membranes. The other pool of stain is located along in the central axis of each connexon, measures 1-2 nm in diameter and 4-5 nm in length, and is restricted to the gap region. On rare occasions, barely discernible linear densities seem to extend from this latter pool of stain and traverse the entire width of the junction. The data indicate the existence of a hydrophilic cavity along the central axis of te connexon which, in most instances, is restricted to the gap region. However, the precise depth to which this cavity may further extend along the connexon axis is still uncertain.

scholarly journals MORPHOLOGICAL CORRELATES OF INCREASED COUPLING RESISTANCE AT AN ELECTROTONIC SYNAPSE

1971 ◽  
Vol 49 (1) ◽  
pp. 173-188 ◽  
Author(s):  
George D. Pappas ◽  
Y. Asada ◽  
M. V. L. Bennett
Keyword(s):  
Electron Microscope ◽  
Schwann Cell ◽  
Extracellular Space ◽  
Physiological Solution ◽  
Mechanical Injury ◽  
Electrotonic Coupling ◽  
Giant Axons ◽  
Cell Processes ◽  
Coupling Resistance ◽  
Hexagonal Network

Close appositions between axonal membranes are present in the septum between adjacent axonal segments of the septate or lateral giant axons of the crayfish Procambarus. In sections the closely apposed membranes appear separated by a space or gap. The use of lanthanum indicates that there may be structures connecting the apposed membranes. The apparent gap is actually a network of channels continuous with the extracellular space. Adjacent axonal segments are electrotonically coupled at the septa. The coupling resistance is increased by mechanical injury of an axon, immersion in low Cl- solutions, and immersion in low Ca++ solutions, followed by a return to normal physiological solution. Septa at which coupling resistance had been measured were examined in the electron microscope. The induced increases in coupling resistance are associated with separation of the junctional membranes (with the exception of the moderate increases during immersion in low Ca++ solutions). Schwann cell processes are present between the separated axonal membranes. When nerve cords in low Cl- solutions are returned to normal physiological solution, coupling, i.e., electrotonic synapses. A model of an electrotonic synapse is proposed in which tween axonal membranes are again found. The association between the morphological and physiological findings provides further evidence that the junctions are the sites of electrotonic coupling, i.e., electrotonic, synapses. A model of an electrotonic synapse is proposed in which intercytoplasmic channels not open to the extracellular space are interlaced with a hexagonal network of extracellular channels between the apposed junctional membranes.

scholarly journals THE STRUCTURAL ORGANIZATION OF THE SEPTATE AND GAP JUNCTIONS OF HYDRA

1972 ◽  
Vol 52 (2) ◽  
pp. 397-408 ◽  
Author(s):  
Arthur R. Hand ◽  
Stephen Gobel
Keyword(s):  
Gap Junctions ◽  
Intercellular Space ◽  
Structural Organization ◽  
Barrier Properties ◽  
Ruthenium Red ◽  
Septate Junction ◽  
Intercellular Coupling ◽  
Lanthanum Hydroxide ◽  
Septate Junctions ◽  
Large Numbers

The septate junctions and gap junctions of Hydra were studied utilizing the extracellular tracers lanthanum hydroxide and ruthenium red. Analysis of the septate junction from four perspectives has shown that each septum consists of a single row of hexagons sharing common sides of 50–60 A. Each hexagon is folded into chair configuration. Two sets of projections emanate from the corners of the hexagons. One set (A projections) attaches the hexagons to the cell membranes at 80–100-A intervals, while the other set (V projections) joins some adjacent septa to each other. The septate junctions generally contain a few large interseptal spaces and a few septa which do not extend the full length of the junction. Basal to the septate junctions the cells in each layer are joined by numerous gap junctions. Gap junctions also join the muscular processes in each layer as well as those which connect the layers across the mesoglea. The gap junctions of Hydra are composed of rounded plaques 0.15–0.5 µ in diameter which contain 85-A hexagonally packed subunits. Each plaque is delimited from the surrounding intercellular space by a single 40-A band. Large numbers of these plaques are tightly packed, often lying about 20 A apart. This en plaque configuration of the gap junctions of Hydra contrasts with their sparser, more widely separated distribution in many vertebrate tissues. These studies conclude that the septate junction may possess some barrier properties and that both junctions are important in intercellular adhesion. On a morphological basis, the gap junction appears to be more suitable for intercellular coupling than the septate junction.

scholarly journals Adaptation of the heart to hypertension is associated with maladaptive gap junction connexin-43 remodeling

2008 ◽  
pp. 7-11
Author(s):  
M Fialová ◽  
K Dlugošová ◽  
L Okruhlicová ◽  
F Kristek ◽  
M Manoach ◽  
...  
Keyword(s):  
Ventricular Fibrillation ◽  
Gap Junctions ◽  
Gap Junction ◽  
Connexin 43 ◽  
Isolated Heart ◽  
Intercellular Junctions ◽  
Membrane Surfaces ◽  
Rat Hearts ◽  
Junction Protein ◽  
Heart Preparation

We hypothesized that hypertension-related myocardial remodeling characterized by hypertrophy and fibrosis might be accompanied by cell-to-cell gap junction alterations that may account for increased arrhythmogenesis. Intercellular junctions and expression of gap junction protein connexin-43 were analyzed in rat heart tissues from both spontaneous (SHR) and L-NAME model of hypertension. Isolated heart preparation was used to examine susceptibility of the heart to lethal ventricular fibrillation induced by low potassium perfusion. Ultrastructure observation revealed enhanced neoformation of side-to-side type while internalization of end-to-end type (intercalated disc-related) of gap junctions prevailed in the myocardium of rats suffering from either spontaneous or L-NAME-induced hypertension. In parallel, immunolabeling showed increased number of connexin43 positive gap junctions in lateral cell membrane surfaces, particularly in SHR. Besides, focal loss of immunopositive signal was observed more frequently in hearts of rats treated with L-NAME. There was a significantly higher incidence of hypokalemia-induced ventricular fibrillation in hypertensive compared to normotensive rat hearts. We conclude that adaptation of the heart to hypertension-induced mechanical overload results in maladaptive gap junction remodeling that consequently promotes development of fatal arrhythmias.

Types of intercellular junctions in teleost ovarian follicles (plecoglossus altivelis)

1978 ◽  
Vol 36 (2) ◽  
pp. 556-557
Author(s):  
K. Toshimori ◽  
C Ōura ◽  
F Yasuzumi
Keyword(s):  
Electron Microscope ◽  
Gap Junctions ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Ovarian Follicles ◽  
The Other ◽  
Follicle Cells ◽  
Plecoglossus Altivelis ◽  
Zonula Occludens ◽  
Intramembraneous Particles

In animal ovarian follicles, many investigators have reported various types of intercellular junctions such as desmosome (macula adherens), gap junction (nexus) and tight junction (zonula occludens). Between adjacent follicle cells, though both desmosomes and gap junctions were clearly presented, no tight junctions were ellucidated by electron microscope excepting Adams and Hertig (guinea pig;1964) and Espey and Stutts (rabbit;1972). On the other hand, between the oocyte and follicle cells, though desmosmes or desmosome-like areas were shown, no gap junctions were recognized to exist excepting Amsterdam et al. (1976) who suggested the presence of small gap junctions on rat oocyte surfaces and Anderson and Albertini (1976) who showed the presence of aggregations of intramembraneous particles on the oocyte surfaces in mouse, rat, rabbit and monkey. Types of intercellular junctions in animal ovarian follicles were not completely understood, because few workers applied freeze-fracture technique to demonstrate junctions excepting Anderson and Albertini (1976).

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