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N J Lane

Publications and source records attributed to N J Lane.

At least 37 records · Page 2Linked to original sources
PubMed1992

Ebselen. Antioxidant capacity in renal preservation.

Ebselen (PZ51) was tested for its ability to inhibit oxidative membrane damage and improve outcome of rabbit kidneys rendered cold ischaemic for 72 hr. In view of the rapid metabolism of ebselen, the antioxidant capacities of its two principal metabolites were first compared with that of the parent drug in an in vitro hepatic microsomal lipid peroxidation system initiated by NADPH/Fe(3+)-ADP. The potent antioxidant activity of ebselen was confirmed but metabolite I (2-glucuronylselenobenzanilide) exhibited no antioxidant potential up to a concentration of 50 microM; metabolite II (4-hydroxy-2-methyl-selenobenzanilide) did inhibit lipid peroxidation but was about 80 times less effective than the parent compound. The storage of rabbit kidneys in hypertonic citrate solution at 0 degrees for 72 hr of cold ischaemia resulted in greatly increased susceptibility to oxidative membrane damage in both the cortex and medulla as determined by the subsequent in vitro formation of two markers of lipid peroxidation (Schiff's bases and thiobarbituric acid-reactive material). Inclusion of ebselen (50 microM) in the flush and storage solution led to a highly significant reduction in these oxidative markers in both regions of the kidney. Intracellular and interstitial oedema was noted in organs subjected to 72 hr cold ischaemia and was reduced by ebselen (50 microM in the flush/storage solution). The rate of post-ischaemic lipid peroxidation was found to correlate well with the extent of oedema in the renal medulla (r = 0.84, P less than 0.001) but no such correlation was found in the cortex. Administration of ebselen (5.5 mg/kg i.v. and 100 microM in the flush/storage solution) did not improve the long-term survival of rabbits following autotransplantation of a single kidney stored for 48 or 72 hr. No protective effect of ebselen could be demonstrated either in terms of graded physiological function or histological outcome.

Animals↗
PubMed1992

Freeze-fracture evidence for a novel restricting junction at the blood-brain barrier of the cuttlefish Sepia officinalis.

The blood-brain barrier in the cuttlefish Sepia officinalis has been studied with the freeze-fracture technique. Previous thin-section electron microscopy showed that a restricting junction is formed between perivascular glial processes in microvessels and venous vessels, and between pericytes in arterial vessels; the restriction appeared not to be a classical zonula occludens or septate junction. In freeze-fracture replicas from brain optic and vertical lobe, endothelial cells, pericytes and perivascular glia could be recognized by their morphology and relation to the vascular lumen. In microvessels, endothelial and pericyte membranes showed sparse but uniform distribution of P-face intramembranous particles, with no particular particle aggregations. Perivascular glial membranes had a higher density of intramembranous particles but again no particle alignments characteristic of known restricting junctions were seen, although clusterings of intramembranous particles resembling gap junctions were present. In larger venous vessels, the perivascular glial layer showed a multilamellated organization, but again no arrays of intramembranous particles were detected, although this should be a favourable site for visualization of the restricting junctions. The walls of arterial vessels showed collagen deposits and cell processes with apparent intracellular myofilamentous profiles, but no intramembranous junctional particle arrays. It is concluded that the junctional zone observed in thin section electron microscopy is not associated with aligned aggregations of intramembranous particles detectable in freeze-fracture replicas, strengthening the evidence that this is a novel type of restricting junction.

Animals↗
PubMed1992

A fibre matrix model for the restricting junction of the blood-brain barrier in a cephalopod mollusc: implications for capillary and epithelial permeability.

A model is proposed for the novel restricting junction forming the blood-brain barrier in a cephalopod mollusc, the cuttlefish Sepia officinalis. The model is based on electron-microscopic findings, from both thin-section and freeze-fracture material, the distribution of electron-dense tracers, and radioisotopic measurements of permeability using small non-electrolytes. Biochemical properties of Sepia plasma proteins are also considered. It is proposed that an effective blood-brain barrier is achieved by a combination of mechanisms. As much as 90% of the Sepia brain microvessel wall is covered by a 'seamless' glial sheath, without intercellular clefts, limiting the number of potential leakage sites. The remaining clefts follow a tortuous course increasing the diffusion path to the neuropile. Entry into the clefts is reduced by a restricting junctional region at the luminal end, characterized by delicate striations spanning the cleft, and forming an effective barrier to both horseradish peroxidase and ionic lanthanum. This is a novel junctional type, different from previously-described vertebrate and invertebrate occluding junctions. It is proposed that the junction acts as a fine-mesh molecular filter, with condensed extracellular material in the cleft, cross-linked and consolidated by bound plasma protein. Cephalopod haemocyanin or its subcomponents are considered likely candidates for the bound protein. The model predicts that blood-brain barrier permeability should be sensitive to the charge structure of the extracellular matrix and the presence of protein, and is analogous to the 'fibre matrix' model of vertebrate capillary permeability. The Sepia blood-brain barrier also highlights the different strategies available for constructing a restricting cell layer, and suggests a possible evolutionary pattern underlying the present range of junctional mechanisms in vertebrate and invertebrate epithelia.

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PubMed1992

Structural domains of the tight junctional intramembrane fibrils.

Freeze-fracture reveals intramembrane fibrils lying along the intermembrane contacts that characterize tight junctions. Tight junctions from a variety of species are reexamined here by rapid freezing prior to freeze-fracture. The tight junction fibril is uprooted alternatively from either the cytoplasmic or the exoplasmic hemibilayer during freeze-cleavage, exposing two distinct but complementary views of its hybrid structure within the same replica. When the transmembrane fibril is uprooted from the exoplasmic hemibilayer it appears on the P-fracture face as a smooth-surfaced cylinder which is sometimes resolved into periodic globular structures. The lack of indication that the P-face cylinder has been pulled out through the opposite membrane half indicates that this domain of the fibril is, in large part, buried in the hydrophobic interior of the membrane. However, when the transmembrane fibril is uprooted from the cytosolic hemibilayer it appears on the E-fracture face as a row of irregular intramembrane particles. The irregular particles on the E-face aspect of the fibril are interpreted as corresponding to transmembrane protein segments that may very well make projections onto the cytosolic surface of the bilayer. En face views of the outermost junction strand between adjacent epithelial cells show periodic lines on the bilayer on each side of the junction which are interpreted as periodic transmembrane protein segments arising from the core structure of the tight junction fibril. If the backbone of the tight junction strand is an inverted cylindrical micelle, it must typically include proteins, which might anchor it to structures outside the membrane bilayer.

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PubMed1991

Morphology of glial blood-brain barriers.

Glial cells, in certain situations in the CNS, may become modified to form the structural basis of the blood-brain barrier. This occurs in more primitive vertebrates, such as the elasmobranch fish, and in some higher invertebrates. In the latter, the outermost glial sheath, often called the perineurium in avascular ganglia, substitutes functionally for the vascular endothelium of higher organisms. The intercellular junctions between the lateral borders of these modified glial or perineurial cells may be of several types. In nearly all cases, adhesive and communicating (gap) junctions are found together with an occluding junctional structure. The latter is assumed to be the morphologic basis of the observed blood-brain barrier. It varies in nature and may be one in which the adjacent cell membranes fuse, partially or completely, to form a classical tight junction, or it may be one in which the cell membranes remain separated by a distinct intercellular cleft. If the latter, the cleft may be straddled by columns or septal ribbons, between which a charged matrix substance may be found. Restrictive linker junctions, recently found to be the basis of the interglial barrier in cephalopod CNS, as well as that of myriapods, are characterized by cross-striations or columns which, in combination with charged residues, inherent either in them or in the associated extracellular matrix, slow down the entry of exogenous molecules. Septate junctions, which occur between glial cells in certain other invertebrates, exhibit intercellular septal ribbons, which do not prohibit paracellular transport of all substances but may slow down the passage of some by virtue of charged moieties. There is an association of cytoskeletal components with these septate, linker, and tight junctions; the role of the cytoskeleton in tight junctions, which can be seen by freeze fracture to be based on simple ridges in insects or a more complex network of them in arachnids, may also be important in the regulation of paracellular permeability. The structural details of the junctions in different groups are summarized and their physiologic implications discussed.

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PubMed1990

Evidence for a transcellular cisternal route across the caecal epithelium of an insect.

The cells of the mesenteric caeca in the midgut of certain insects possess a labyrinth of transepithelial cisternae. Their existence can be seen in thin sections of lanthanum-incubated tissue, where the tracer enters not only the intercellular clefts but also membranous cisternae which are inpocketings from, and, in continuity with, both the lateral clefts and basal membrane. These infoldings, which are numerous, run from the basal or lateral surfaces into the perinuclear region of the cells, where they are found, laden with lanthanum, as smooth cisternae or vesicles in the peripheral cytoplasm near the plasma membrane. These can be followed in serial sections and are quite distinct from other sub-surface cisternae of the lateral borders which are studded with ribosomes on the cytoplasmic surface. Near the luminal surface, tracer-laden structures in the form of vesicles and granules become increasingly predominant over those in the form of cisternae. Freeze-fracture replicas confirm the above observations, in that the plasma membrane of the intercellular cleft can be characterized as such unequivocally, since it exhibits smooth septate junctional E face grooves and P face ridges. Lateral infoldings, cisternae and vesicles can be seen arising directly from these junction-bearing membranes. The transepithelial cisternae and vesicles may be the morphological basis of an insect transcellular transport system, comparable to the tubulo-cisternal endoplasmic reticulum present in the transporting secretory and absorptive epithelia of vertebrate tissues. However, in insect midgut caecal epithelia, the cisternae appear to be, albeit presumably transiently, in direct continuity with the extracellular space, forming a plasma membrane reticular system which seems not to be the case with the tubulo-cisternal endoplasmic reticulum which terminates in subsurface cisternae.

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PubMed1990

Changes in intercellular junctions during peripheral nerve regeneration in insects.

Peripheral nerves of the adult cockroach have been cut and the changes in glial cells followed during the subsequent process of regeneration. After three to four weeks of regrowth, the severed tips of nerves were examined by freeze-fracture to assess the state of intercellular junctions between the perineurial sheath cells as well as the underlying glial cells. Both pleated septate and gap junctions were found in the immature state; their intramembranous particle (IMP) distribution was characteristic of junctions in the process of assembly, since the IMPs were irregularly and loosely arrayed in contrast with the parallel septate junctional IMP rows and gap junctional plaques found in the fully regenerated or control tissues. These junctional stages resembled those occurring in developing embryonic or metamorphosing insect tissues.

Animals↗
PubMed1989

Novel arthropod cell junctions with restrictive intercellular 'linkers'.

The peripheral glial cells that surround the components of the avascular CNS in certain groups of primitive arthropods are characterized by unusual intercellular junctions. In the centipedes and millipedes (Myriapoda), these glial cells are associated by interconnecting filamentous 'linkers' which produce a reduction, but not an occlusion, of the intercellular cleft; these are interposed between conventional gap junctions. In replicas, the freeze-cleave images are of loosely aggregated gap junctional connection plaques, fracturing on to the extracellular membrane half leaflet (E face), together with linear alignments of intramembranous particles (IMPs) and furrows; complementary P face ridges also occur. Exogenous tracers appear unable to penetrate beyond these junction-rich glial clefts, possibly by binding to the 'linkers' or extracellular matrix between them. Peripheral glial cells in the cerebral ganglion of the horseshoe crab, Limulus, are also characterized by linear IMP arrays; in this case they primarily exhibit E face grooves and complementary ridges of P face IMPs, which also do not produce complete membrane fusion. These, too, are intimately associated with gap junctional plaques of E face particles or P face pits. These intramembranous particle rows are novel structural modifications, called here 'linker' junctions, and are quite distinct from conventional tight or septate junctions found between the outer glial cells in more highly evolved arthropods such as the insects and arachnids. They seem to represent a new category of intercellular junction.

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PubMed1988

Tissue and species conservation of the vertebrate and arthropod forms of the low molecular weight (16-18000) proteins of gap junctions.

Gap junctions have been isolated from four murine tissues, from rat and Xenopus laevis liver, and from Nephrops norvegicus (Norway lobster) hepatopancreas. The preparations of gap junctions from each vertebrate tissue contain a single major protein, Mr 16,000, and those from Nephrops hepatopancreas a protein, Mr 18,000. Immunocytochemical studies using affinity-purified antibodies raised against gap junctions from Nephrops show the junctional origin of the 18k protein. Immunological studies using Western blotting and biochemical studies using tryptic peptide mapping show no significant differences between the 16k junctional proteins of mouse and hence provide no evidence of tissue variation. These studies also suggest that the mouse, rat, and Xenopus 16k proteins and the Nephrops 18k protein share some common structural features.

Animals↗
PubMed1988

Actin filaments are associated with the septate junctions of invertebrates.

Septate junctions are almost ubiquitous in the tissues of invertebrates but are never found in those of vertebrates. In spite of their widespread occurrence and hence obvious importance to the invertebrates, their precise function has remained elusive although they have been variously considered to be regions of cell-cell coupling, permeability barriers or adhesion sites. This report demonstrates that elements of the cytoskeletal system insert into the cytoplasmic face of septate junctions. Actin filaments, identified by virtue of their capacity to bind the S1 subfragment of rabbit myosin, are associated with the membranes of septate junctions. Cytochalasin D, an actin depolymerizer, leads to disorganization of the intramembrane components of these junctions. These data suggest that a primary role of septate junctions could be to maintain intercellular cohesion and hence tissue integrity. The assembly and localization of these junctions may be mediated, directly or indirectly, by the cytoplasmic actin filaments associated with their lateral membranes.

Actins↗
PubMed1988

The initial stages in the action of an insecticidal delta-endotoxin of Bacillus thuringiensis var. israelensis on the epithelial cells of the malpighian tubules of the insect, Rhodnius prolixus.

The effects of the 27 X 10(3) Mr insecticidal delta-endotoxin from Bacillus thuringiensis var. israelensis have been studied using, as a model system, isolated insect Malpighian tubules. At all concentrations of the toxin higher than 1 microgram ml-1 (4 X 10(-8) moll-1) applied to the outer surface of the tubules, fluid secretion failed within about 30 min. Except at very high concentrations, where failure always takes at least 30 s, there was an inverse relationship between the concentration of toxin and the time of failure of toxin-treated tubules. During exposure to toxin, the tubules were initially unaffected for a relatively long period and then rapid failure occurred. If the tubules were removed into toxin-free saline just before failure would have occurred, fluid secretion remained normal for at least 2 h, but on return to the origin toxin-containing saline failure was almost immediate. The toxin was found not to bind to the basement membrane. Ultrastructural changes became evident as tubule failure occurred. These initially involved modifications to the basal side of the cells, but later also to the luminal microvilli. Intercellular junctions became disassociated and cytoplasmic vacuolization occurred. The population of intramembranous particles in the basal membranes became reduced with time. Our findings suggest the following hypothesis for the initial stages in the interaction of the toxin with the tubules. Toxin molecules attach to the accessible cell membranes progressively and irreversibly. They do not readily associate by diffusing laterally in the membrane, so that toxic effects develop only when sufficiently large numbers of them attach close together. The molecules may then associate in some way as a complex, perhaps forming a pore in the membrane. Relatively few such pores lead rapidly to cell failure and death.

Animals↗
PubMed1987

Freeze-fracture studies on the giant axon and ensheathing Schwann cells of the squid.

The giant axons and encompassing sheaths from the stellar nerves of the squids Sepioteuthis sepioidea and Loligo forbesi have been analysed by freeze-fracture. The axolemma exhibits many intramembranous particles (IMPs) that fracture onto the cytoplasmic membrane half-leaflet (P-face); the larger IMPs may be aggregated into clusters. Axoplasmic subsurface cisternae are found beneath this membrane. Clustered or aligned arrays of P-face IMPs are also found on the membranes of the Schwann cells that intimately encapsulate the giant axons as well as 'capitate' projections of Schwann cells into the axons. When adjacent Schwann cells abut directly against one another, aligned E-face IMPs are found along the fracture plane of the upturning membranes. These E-face alignments of IMPs have complementary furrows on the Schwann cell membranes which exhibit no complementary structure on the axolemma as they represent the clefts between adjacent glial cells. The other Schwann cell membranes exhibit P-face dimples and E-face (extracellular membrane half-leaflet) protuberances which may reflect endo- or exocytotic activity; alternatively they may represent caveolae. Comparable structures are occasionally observed at axo-glial interfaces. However, those in the Schwann cell membrane could be part of the transverse tubular lattice system which also exists in adaxonal glia. Beyond the Schwann cells, layers of endoneurial cells (fibrocytes) are interleaved by collagen-filled spaces. These cells exhibit extensive cross-fractured intracellular invaginations as well as inpushings of the extracellular matrix material. Their membranes exhibit a large number of IMPs.

Animals↗
PubMed1987

The lack of a structured blood-brain barrier in the onychophoran Peripatus acacioi.

Onychophorans are 'living fossils' frequently purported to have evolved from the same ancestor as the arthropods and annelids. In the CNS of Peripatus acacioi, beneath an outer acellular neural lamella, glial cells ensheath the cerebral ganglion and the nerve cords. These glial cells are, however, attenuated and rather few in number and, although they interdigitate with one another, they seem to lack intercellular junctions. Exogenous tracers penetrate between them and into the underlying neuropile, suggesting that there is no structural blood-brain barrier. Throughout the nervous tissue, extracellular spaces occur which contain banded collagen fibrils embedded in a matrix material. Thin glial cell processes, characterized by dense filaments, surround these regions and frequently form hemi-desmosomes with the extracellular matrix. The peripheral nerve cell bodies have a range of diameters; some have the characteristics of neurosecretory neurons. Granules in such neurons are produced by the Golgi saccules and associated fenestrated membranes which also possess many coated vesicles. Comparable granules are also found in axonal tracts, but no distinct peripheral neurohaemal areas have been found. Lysosomes are common in the nerve cell bodies and are frequently in the form of multivesicular bodies or large phagocytic vacuoles. Beneath the outer nerve cells lie many tracheae, arranged as a ring around the central neuropile which consists of glial processes, extracellular matrix, axons and nerve terminals. These nerve terminals occur throughout the central neuropile and are characterized by dense pyramidal presynaptic specializations and postsynaptic subsurface cisternae. The nervous system of Peripatus is relatively simple in its organization, in the lack of glial intercellular junctions and in the ready accessibility of substances from the external milieu.

Animals↗
PubMed1986

The intramembrane structure of septate junctions based on direct freezing.

Smooth septate junctions from the midgut of the cricket, Acheta, and the horseshoe crab, Limulus, as well as Hydra-type septate junctions from the epidermis of Hydra have been studied by freeze-fracture after direct freezing using the liquid helium-cooled copper block/slam freezing method. The exoplasmic fracture face at both types of septate junction exhibits rows of closely packed but irregularly shaped intramembrane particles. Complementary to these particle rows, on the protoplasmic fracture face, are sharply defined grooves with a periodic variation in depth and width that was conspicuous in Hydra but less well defined in arthropods. The closely packed, irregular particles on the exoplasmic faces could represent plastically deformed portions of transmembrane proteins pulled through the bilayer during freeze-fracture. On the basis of this interpretation, the grooves on the protoplasmic faces represent a confluence of the bilayer disruptions occurring during fracturing. The structures observed here are different from those reported in replicas of glutaraldehyde-fixed and glycerol-cryoprotected tissue, in which the intramembrane junctional components partition with the protoplasmic face and often assume the appearance of continuous cylinders. This comparison illustrates some of the artifacts associated with freeze-fracturing and shadowing. On the basis of a comparison of freeze-fracture replicas and sections of lanthanum-infiltrated tissues, the relationship between intramembrane junctional components and intercellular septal elements is analysed.

Animals↗
PubMed1986

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

Animals↗
PubMed1985

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

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.

Animals↗
PubMed1985

Embryonic development of glial cells and their junctions in the locust central nervous system.

The embryonic development of the specialized glial cells that form the perineurial blood-brain barrier in the locust CNS has been studied by freeze-fracture and tracer uptake. These cells migrate to form bracelet cell arrangements around the nervous tissues between day 4 to day 10 of embryonic differentiation which lasts 14 days in toto. A number of different kinds of intercellular junction form between the bracelet cells from day 8 to day 13 of development. These include gap junctions with features characteristic of arthropods, which seem to assemble by lateral migration of 13-nm E face intramembranous particles (IMPs), which ultimately cluster to form a large number of mature plaques of varying diameters. Less numerous are tight junctions which serve to restrict entry of exogenous molecules, including lanthanum and cationic ferritin, thereby forming the blood-brain barrier; these appear to assemble by migration of individual 8- to 10-nm P face IMPs into ridges which are found between the overlapping fingers of the perineurial bracelet cell processes. Septate junctions also mature at this stage in embryonic development by apparent assembly of IMPs into characteristic aligned rows; these may serve to slow down the entry of positively charged molecules as well as being adhesive, although anionic ferritin may leak into the CNS even after septate and tight junction formation. The observed changes in cellular associations and the formation of the blood-brain barrier coincide with the onset of mature neuronal electrical properties and spontaneous synaptic input.

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