Comparative analysis of crystalline lens gap junctions

1984 ◽  
Vol 42 ◽  
pp. 114-117
Author(s):  
J.R. Kuszak ◽  
Y.H. Shek ◽  
K.C. Carney ◽  
J.L. Rae
Keyword(s):  
Comparative Analysis ◽  
Cell Membrane ◽  
Gap Junctions ◽  
Gap Junction ◽  
Transmembrane Proteins ◽  
Crystalline Lens ◽  
Species Variation ◽  
Intracellular Location ◽  
Fiber Cells ◽  
Electrophysiological Studies

In freeze-etch replicas, gap junctions are identifiable on PF faces as raised plaques of membrane with aggregated hexameric transmembrane proteins. On EF faces, gap junctions are seen as imprinted membrane plaques that have pits corresponding to the connexons of the gap junction from the previously conjoined cell. By these criteria, several investigators have demonstrated that gap junctions are more numerous between fiber cells of the crystalline lens than between cells of any other organ. A review of this literature suggests that there is considerable species variation in the percent of fiber cell membrane specialized as gap junction in crystalline lenses. In electrophysiological studies, cells are considered to be electrotonically coupled to one another if an intracellular potential change can be elicited at essentially all locations when current is applied at a single intracellular location. Electrotonic coupling is presumed to be mediated by gap junctions.

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.

Activated macrophages inhibit enterocyte gap junctions via the release of nitric oxide

2008 ◽  
Vol 294 (1) ◽  
pp. G109-G119 ◽  
Author(s):  
Rahul J. Anand ◽  
Shipan Dai ◽  
Christopher Rippel ◽  
Cynthia Leaphart ◽  
Faisal Qureshi ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Gap Junctions ◽  
Gap Junction ◽  
Intestinal Inflammation ◽  
Lucifer Yellow ◽  
Close Association ◽  
Activated Macrophages ◽  
Intracellular Location ◽  
Gap Junction Communication ◽  
No Release

Enterocytes exist in close association with tissue macrophages, whose activation during inflammatory processes leads to the release of nitric oxide (NO). Repair from mucosal injury requires the migration of enterocytes into the mucosal defect, a process that requires connexin43 (Cx43)-mediated gap junction communication between adjacent enterocytes. Enterocyte migration is inhibited during inflammatory conditions including necrotizing enterocolitis, in part, through impaired gap junction communication. We now hypothesize that activated macrophages inhibit gap junctions of adjacent enterocytes and seek to determine whether NO release from macrophages was involved. Using a coculture system of enterocytes and macrophages, we now demonstrate that “activation” of macrophages with lipopolysaccharide and interferon reduces the phosphorylation of Cx43 in adjacent enterocytes, an event known to inhibit gap junction communication. The effects of macrophages on enterocyte gap junctions could be reversed by treatment of macrophages with the inducible nitric oxide synthase (iNOS) inhibitor l-Lysine ω-acetamidine hydrochloride (l-NIL) and by incubation with macrophages from iNOS−/− mice, implicating NO in the process. Activated macrophages also caused a NO-dependent redistribution of connexin43 in adjacent enterocytes from the cell surface to an intracellular location, further suggesting NO release may inhibit gap junction function. Treatment of enterocytes with the NO donor S-nitroso- N-acetylpenicillamine (SNAP) markedly inhibited gap junction communication as determined using single cell microinjection of the gap junction tracer Lucifer yellow. Strikingly, activated macrophages inhibited enterocyte migration into a scraped wound, which was reversed by l-NIL pretreatment. These results implicate enterocyte gap junctions as a target of the NO-mediated effects of macrophages during intestinal inflammation, particularly where enterocyte migration is impaired.

Connexin 43 ubiquitination determines the fate of gap junctions: restrict to survive

2015 ◽  
Vol 43 (3) ◽  
pp. 471-475 ◽  
Author(s):  
Teresa M. Ribeiro-Rodrigues ◽  
Steve Catarino ◽  
Maria J. Pinho ◽  
Paulo Pereira ◽  
Henrique Girao
Keyword(s):  
Plasma Membrane ◽  
Gap Junctions ◽  
Gap Junction ◽  
Intercellular Communication ◽  
Connexin 43 ◽  
Transmembrane Proteins ◽  
Post Translational Modifications ◽  
Gap Junction Intercellular Communication

Connexins (Cxs) are transmembrane proteins that form channels which allow direct intercellular communication (IC) between neighbouring cells via gap junctions. Mechanisms that modulate the amount of channels at the plasma membrane have emerged as important regulators of IC and their de-regulation has been associated with various diseases. Although Cx-mediated IC can be modulated by different mechanisms, ubiquitination has been described as one of the major post-translational modifications involved in Cx regulation and consequently IC. In this review, we focus on the role of ubiquitin and its effect on gap junction intercellular communication.

scholarly journals Lens intracellular hydrostatic pressure is generated by the circulation of sodium and modulated by gap junction coupling

2011 ◽  
Vol 137 (6) ◽  
pp. 507-520 ◽  
Author(s):  
Junyuan Gao ◽  
Xiurong Sun ◽  
Leon C. Moore ◽  
Thomas W. White ◽  
Peter R. Brink ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Hydrostatic Pressure ◽  
Gap Junctions ◽  
Gap Junction ◽  
Mouse Models ◽  
Single Layer ◽  
Wild Type Mouse ◽  
Pressure Sensing ◽  
Fiber Cells ◽  
Gap Junction Channels

We recently modeled fluid flow through gap junction channels coupling the pigmented and nonpigmented layers of the ciliary body. The model suggested the channels could transport the secretion of aqueous humor, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be just a few mmHg and difficult to measure. In the lens, however, there is a circulation of Na+ that may be coupled to intracellular fluid flow. Based on this hypothesis, the fluid would cross hundreds of layers of gap junctions, and this might require a large hydrostatic gradient. Therefore, we measured hydrostatic pressure as a function of distance from the center of the lens using an intracellular microelectrode-based pressure-sensing system. In wild-type mouse lenses, intracellular pressure varied from ∼330 mmHg at the center to zero at the surface. We have several knockout/knock-in mouse models with differing levels of expression of gap junction channels coupling lens fiber cells. Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels. When the lens’ circulation of Na+ was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally. These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.

Multiple structural types of gap junctions in mouse lens

1993 ◽  
Vol 106 (1) ◽  
pp. 227-235 ◽  
Author(s):  
W.K. Lo ◽  
T.S. Reese
Keyword(s):  
Epithelial Cells ◽  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Freeze Substitution ◽  
Fiber Types ◽  
Fiber Cells ◽  
Structural Types

Gap junctions in the epithelium and superficial fiber cells from young mice were examined in lenses prepared by rapid-freezing, and processed for freeze-substitution and freeze-fracture electron microscopy. There appeared to be three structural types of gap junction: one type between epithelial cells and two types between fiber cells. Epithelial gap junctions seen by freeze-substitution were approximately 20 nm thick and consistently associated with layers of dense material lying along both cytoplasmic surfaces. Fiber gap junctions, in contrast, were 15–16 nm (type 1) or 17–18 nm thick (type 2), and had little associated cytoplasmic material. Type 1 fiber gap junctions were extensive in flat expanses of cell membrane and had a thin, discontinuous central lamina, whereas type 2 fiber gap junctions were associated with the ball-and-socket domains and exhibited a dense, continuous central lamina. Both types of fiber gap junction had a diffuse arrangement of junctional intramembrane particles, whereas particles and pits of epithelial gap junctions were in a tight, hexagonal configuration. The type 2 fiber gap junctions, however, had a larger particle size (approximately 9 nm) than the type 1 (approximately 7.5 nm). In addition, a large number of junctional particles typified the E-faces of both fiber types but not the epithelial type of gap junction. Gap junctions between fiber and epithelial cells had structural features of type 1 fiber gap junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Calmodulin-mediated gating of lens gap junction channels in vesicles

1984 ◽  
Vol 42 ◽  
pp. 134-137
Author(s):  
Camillo Peracchia ◽  
Stephen J. Girsch
Keyword(s):  
Gap Junctions ◽  
Freeze Fracture ◽  
Orthogonal Arrays ◽  
Eye Lens ◽  
Lens Fiber ◽  
Cell Coupling ◽  
Particle Spacing ◽  
Fiber Cells ◽  
Gap Junction Channels ◽  
Communicating Junctions

The fiber cells of eye lens communicate directly with each other by exchanging ions, dyes and metabolites. In most tissues this type of communication (cell coupling) is mediated by gap junctions. In the lens, the fiber cells are extensively interconnected by junctions. However, lens junctions, although morphologically similar to gap junctions, differ from them in a number of structural, biochemical and immunological features. Like gap junctions, lens junctions are regions of close cell-to-cell apposition. Unlike gap junctions, however, the extracellular gap is apparently absent in lens junctions, such that their thickness is approximately 2 nm smaller than that of typical gap junctions (Fig. 1,c). In freeze-fracture replicas, the particles of control lens junctions are more loosely packed than those of typical gap junctions (Fig. 1,a) and crystallize, when exposed to uncoupling agents such as Ca++, or H+, into pseudo-hexagonal, rhombic (Fig. 1,b) and orthogonal arrays with a particle-to-particle spacing of 6.5 nm. Because of these differences, questions have been raised about the interpretation of the lens junctions as communicating junctions, in spite of the fact that they are the only junctions interlinking lens fiber cells.

Early ossicle growth in the regenerating disc of a brittle star

1994 ◽  
Vol 52 ◽  
pp. 364-365
Author(s):  
M. Shlepr ◽  
R. L. Turner
Keyword(s):  
Cell Membrane ◽  
Light Microscopy ◽  
De Novo ◽  
Current Model ◽  
Syncytium Formation ◽  
Brittle Star ◽  
Intracellular Location ◽  
Limited Volume ◽  
Tissue Calcification

Calcification in the echinoderms occurs within a limited-volume cavity enclosed by cytoplasmic extensions of the mineral depositing cells, the sclerocytes. The current model of this process maintains that the sheath formed from these cytoplasmic extensions is syncytial. Prior studies indicate that syncytium formation might be dependent on sclerocyte density and not required for calcification. This model further envisions that ossicles formed de novo nucleate and grow intracellularly until the ossicle effectively outgrows the vacuole. Continued ossicle growth occurs within the sheath but external to the cell membrane. The initial intracellular location has been confirmed only for elements of the echinoid tooth.The regenerating aboral disc integument of ophiophragmus filograneus was used to test the current echinoderm calcification model. This tissue is free of calcite fragments, thus avoiding questions of cellular engulfment, and ossicles are formed de novo. The tissue calcification pattern was followed by light microscopy in both living and fixed preparations.

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.

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