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PubMed1983

Electron microscopic serial section analysis of nodes of Ranvier in lumbosacral spinal roots of the cat: ultrastructural organization of nodal compartments in fibres of different sizes.

The general ultrastructural organization of nodes of Ranvier in peripheral nerve fibres from 2 to 20 microns in diameter (D) was investigated in the adult cat using serially sectioned ventral and dorsal spinal roots. The study was performed in order to collect and systematize information considered necessary for a morphometric analysis of the node of Ranvier. In all cases a node of Ranvier could be divided into a central nodal axon segment and a surrounding nodal Schwann cell compartment. The latter included a nodal gap matrix substance, more or less overlapping nodal Schwann cell collars and, as a rule, also a Schwann cell brush-border emanating from the nodal Schwann cell collars and occupying the nodal gap. The relative size and the organization level of the nodal Schwann cell compartment increased with increasing fibre size up to a fibre diameter of 8-10 microns. At this fibre size the nodal gap was of a fairly even height (1 micron) all around the nodal axon and contained a thick brush-border of densely packed, more or less radially arranged Schwann cell microvilli. In very small fibres (D less than 3 microns) the nodal gap was low (less than 0.1 microns) and contained no or few microvilli. In fibres greater than 10 microns in diameter the relative size and the degree of structural order of the nodal Schwann cell compartment decreased with increasing fibre size. Drastic sectorial variations in nodal gap height and local thinning-out of the brush-border became prominent features in the largest fibres. The possible in vivo organization of the nodal Schwann cell compartment is discussed. Preliminary calculations indicate that the extracellular space directly surrounding the nodal axon might be quite small and that the area open for free communication between this extracellular space and the endoneurial space might be very much restricted, measuring as little as 2% of the area of the nodal axolemma. Algorithms for calculating various nodal structural parameters are discussed.

Animals↗
PubMed1991

Intracellular localization of group II phospholipase A2 in rat vascular smooth muscle cells and its possible relationship to eicosanoid formation.

We investigated the localization of group II phospholipase A2 (PLA2-II) in rat vascular smooth muscle cells (VSMCs) by applying immunofluorescence and immunoelectron microscopy with its polyclonal antibody. In unstimulated cells, no immunolabelling was detected in the cells. On the other hand, in the cells stimulated with tumor necrosis factor (TNF) and/or forskolin (FK), intense fluorescence was detected in the cytoplasm. The immunoperoxidase reactions were detected in the cisternae of rough endoplasmic reticulum (rER), trans-cisternae of Golgi apparatus, and small vesicles beneath the plasma membrane. Western blot analysis showed VSMCs secrete PLA2-II after stimulation. Secreted PLA2-II was associated with the plasma membrane and extracellular matrix. Colchicine inhibited PLA2-II synthesis and its secretion to the extracellular space. These observations indicate that in VSMCs PLA2-II is synthesized at rER. transported to Golgi apparatus, discharged into extracellular space via the small vesicles, and microtubules may concern with its process. Furthermore, in VSMCs treated with TNF or TNF + FK, prostaglandin E2 formation was also increased. Actinomycin D and cycloheximide inhibited the potentiation of the prostaglandin E2 formation induced by TNF or TNF + FK, indicating that both RNA and protein synthesis are required for the potentiation. These results suggest an involvement of PLA2-II in the prostaglandin formation.

Animals↗
PubMed1981

Differential effects of ouabain and 2,4-dinitrophenol on contractile tension of and on sodium and calcium efflux from frog heart ventricular strips.

1 The efflux, from heart ventricular strips of Rana pipiens, of sodium ((22)Na) and calcium ((45)Ca) was measured simultaneously.2(22)Na efflux could be resolved into two first order kinetic components: k(I) = 0.105 min(-1), thought to represent efflux from the extracellular space, and k(II) = 0.0182 min(-1) representing efflux from the cells.3(45)Ca efflux was also resolved into an extracellular component, k(I) = 0.1216 min(-1); and an intracellular one, k(II) = 0.0102 min(-1). (45)Ca k(II) was greatly increased by 2,4-dinitrophenol (DNP), but unchanged by caffeine. This suggests that it represents a mitochondrial calcium compartment.4(22)Na k(II) was not changed by DNP. This indicates that, at the time of DNP addition, (22)Na was passively bound to undefined intracellular components.5 Ouabain (10(-6) M) decreased (45)Ca efflux (k(II)) initially but at later periods slightly increased it. The former effect is thought to be due to an action at the plasma membrane level, while the latter probably represents an increased exchangeability of mitochondrial calcium. The same effects were always found when ouabain was applied at different times of strip superfusion.6 Ouabain (0.25 to 4 muM) did not decrease the k(II) of (22)Na efflux. Kinetic reasons are presented which indicate that, in this preparation, the activity of the sodium pump may be too fast to be measured by means of (22)Na efflux, therefore these findings do not necessarily mean that ouabain does not inhibit active sodium transport.7 The time course of the inotropic effect of ouabain was also studied in ventricular strips of Rana pipiens heart that were stimulated at 0.2 Hz with biphasic, 2 ms pulses of supramaximal intensity, and incubated in Ringer solution containing 1.1 mM calcium, or in ;calcium-free' Ringer (residual calcium: 5.2 muM), or in ;calcium-free' Ringer with 0.1 mM of the calcium chelator ethyleneglycol bis (beta-aminoethylether) N,N'-tetraacetic acid (EGTA).8 In Ringer, the inotropic effect of ouabain was already observed at 5-10 s after steroid addition, even with the lowest concentration tested (0.25 muM), while signs of toxicity appeared only after 15 min in 4 muM ouabain, the highest concentration used.9 When the strips were incubated in ;calcium-free' Ringer solution, force of contraction decayed to 1-2% of that in 1.1 mM calcium. Addition of 4 muM ouabain to these hypodynamic strips led to a progressive increase in contractile force of up to 300%, that started after a 50 s latency period. No signs of toxicity were observed.10 Incubation of the strips in EGTA-Ringer also reduced contractile force to about 2% of that in Ringer, and 4 muM ouabain also increased force of contraction by approximately the same amount as seen in ;calcium-free' Ringer, but the effect began after a 10 min latency period. The concentration of calcium ion (Ca(2+)) in the extracellular space of strips incubated in EGTA-Ringer, was approximately 800 fold lower than in Ringer, and 60 fold lower than in ;calcium-free' Ringer solution.11 Caffeine (20 mM) induced, in strips previously incubated for 1 h in 4.4 mM calcium Ringer solution plus 10(-6) M ouabain, a marked initial contracture, that relaxed spontaneously, and was followed by slow waves of contracture. This was not observed if the strips were incubated, prior to caffeine, in 4.4 mM calcium Ringer without ouabain, or in 1.1 mM calcium Ringer solution that contained 10(-6) M ouabain.12 Based on these findings, a hypothesis that can explain the inotropic effect of cardioactive steroids is presented.

2,4-Dinitrophenol↗
PubMed1993

Atypical granules in the eyes of the white mutant of Drosophila melanogaster are lysosome-related organelles.

In the pigment cells of the white mutant of Drosophila melanogaster, as described earlier, two types of abnormal granules are found by conventional electron microscopy. However, both types of abnormal granules, in addition to those in pigment cell invaginations, are also present in the cytoplasm of the photoreceptor cells. Three enzymes (acid phosphatase, peroxidase, and tyrosinase) are localized within the eyes of wild type and white mutant Drosophila melanogaster by electron microscopy. Peroxidase activity is present in lamellar bodies close to the rhabdomeral microvilli of both fly types. However the organelles containing peroxidase activity are 6-fold more frequent in the wild type than in the mutant. Acid phosphatase is present in lamellar bodies between and at the bases of the rhabdomeral microvilli of the wild type, as well as in ommochrome granules of the photoreceptor cells. In the white mutant, however, acid phosphatase was located in electron lucent vacuoles in the cytoplasm of the receptor cells. These acid phosphatase-positive vacuoles also contained both types of abnormal granules. The latter result indicates that abnormal granules in the receptor cells originate from lysosomal degradation and that targeting of lysosomal enzymes is altered in the white mutant. Due to the tyrosinase activity in the hemolymph of flies, the extracellular spaces are electron dense after DOPA incubation. Since some abnormal granules within the photoreceptor cells are not surrounded by an extracellular space, they can be assumed to originate within the photoreceptor cells.

Acid Phosphatase↗
PubMed2000

Aspects of the pathology and etiology of 'drippy gill' disease of the cultivated mushroom Agaricus bisporus.

Agaricus bisporus sporocarps exhibiting characteristic 'drippy gill' symptoms from a natural outbreak were examined. Discrete bacterial droplets on the hymenial lamellae often coalesced to form ribbons of bacterial ooze. Longitudinal splits on the stipe were lined with a similar bacterial ooze. Bacteria isolated from both the hymenium and stipe were identified as Pseudomonas agarici, and were confirmed to be the causal organism by satisfying Koch's postulates. By light and transmission electron microscopy, the causal bacteria were found to colonize the extrahyphal spaces and degrade the extracellular matrix within affected sporocarps. Degradation of the extracellular matrix was shown to reduce the integrity of the sporocarp, and result in stipe splitting and hymenium disruption. In artificial inoculations of the pileus, bacteria were shown to exist predominantly in sporocarp tissue below the point of inoculation and above affected areas of the hymenium, indicating an approximately vertical passage through the sporocarp via the extracellular spaces. The dissolution of the extracellular matrix, and the observed failure of the bacterium to produce a toxin active against A. bisporus, allow the bacteria to pass through protective membranes unnoticed, and infect the stipe and hymenium prior to veil break. These observations dispel previous assumptions of intrahyphal existence and transmission. In the few instances in which the bacteria were observed to be intrahyphal, the host fungal cell wall was often broken, suggesting intrahyphal existence was opportunistic rather than obligatory. The taxonomic position of a bacterium isolated previously from sporocarps exhibiting symptoms similar to those of drippy gill was determined by examining the biochemical and nutritional profiles of the bacterium, and comparing them with other Pseudomonas agarici isolates.

Agaricus↗
PubMed1971

Morphological correlates of increased coupling resistance at an electrotonic synapse.

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.

Animals↗
PubMed1977

Ultrastructural basis of impulse propagation failure in a nonbranching axon.

The morphological basis of intermittent conduction failure in the excitor axon innervating the crayfish opener and stretcher muscles was investigated using the electron microscope. The connective tissue component of the sheath surrounding the axon was found consistently to be thinner in the region at which blocking occurs than in control regions located one cm either proximally or distally, at which blocking does not occur. Otherwise in these regions differences in the width of the periaxonal spaces, the length or width of the mesaxons, the density of mitochondria, the width of the adaxonal glial cell layer, or the structure of lamination of the sheath are not observed. Because of the thinner connective tissue component of the sheath in the joint region, neighboring axons are distributed more densely around the excitor, and the volume of the extracellular space is reduced. The possibility that the reduced extracellular space might allow excessive accumulation of potassium during repetitive discharge, causing conduction block, is discussed. Alternative mechanisms consistent with this morphology are also considered.

Animals↗
PubMed1993

Strontium, a tracer to study the transport of calcium in mineralizing tissues by electron probe microanalysis.

In growth plate cartilage the mineralization starts extracellularly in the lower hypertrophic zone. The mineral formed is the calcium phosphate apatite. Enough calcium and phosphate must be available at the mineralization front as well as in regions with proceeding mineralization. There must be a transport of Ca (and phosphate) to these sites. Electron probe X-ray microanalysis is a well established method to analyze element concentrations in small volumes, but it cannot discriminate isotopes. Strontium is similar to Ca in its chemical and biological behaviour and is therefore a suitable tracer to investigate the transport of Ca. Small amounts of Sr (0.1 g per kg body weight) were administered intraperitoneally to young rats. After definite intervals of time ranging from 10 to 120 min, 2-4 rats were killed. On freeze dried cryosections the Sr/Ca ratio of the serum and of the intra- and extracellular space of the growth plate were measured. The Sr/Ca ratio reaches its maximum after about 10 min in the serum and after 20 min in the extracellular space of growth plate cartilage. The intracellular Sr/Ca ratio shows large variations because of the low intracellular Ca and Sr concentration, and is lower than the extracellular ratio for times shorter than 30 min. No significant differences were found between the different cell zones of the unmineralized growth plate cartilage. The results demonstrate that the transport of Ca to the growth plate cartilage is relatively fast and that in growth plate cartilage, Ca is transported extracellularly, not intracellularly.

Animals↗
PubMed1999

Animal plasma membrane energization by proton-motive V-ATPases.

Proton-translocating, vacuolar-type ATPases, well known energizers of eukaryotic, vacuolar membranes, now emerge as energizers of many plasma membranes. Just as Na(+) gradients, imposed by Na(+)/K(+) ATPases, energize basolateral plasma membranes of epithelia, so voltage gradients, imposed by H(+) V-ATPases, energize apical plasma membranes. The energized membranes acidify or alkalinize compartments, absorb or secrete ions and fluids, and underwrite cellular homeostasis. V-ATPases acidify extracellular spaces of single cells such as phagocytes and osteoclasts and of polarized epithelia, such as vertebrate kidney and epididymis. They alkalinize extracellular spaces of lepidopteran midgut. V-ATPases energize fluid secretion by insect Malpighian tubules and fluid absorption by insect oocytes. They hyperpolarize external plasma membranes for Na(+) uptake by amphibian skin and fish gills. Indeed, it is likely that ion uptake by osmotically active membranes of all fresh water organisms is energized by V-ATPases. Awareness of plasma membrane energization by V-ATPases provides new perspectives for basic science and presents new opportunities for medicine and agriculture.

Animals↗
PubMed1998

Suppression of cell adhesion and spreading activities of fibronectin by arginine-specific ADP-ribosyltransferase from chicken polymorphonuclear leukocytes.

Arginine-specific ADP-ribosyltransferase present in secretory granules of chicken polymorphonuclear leukocytes (so-called heterophils) was shown to be released into the extracellular space by secretagogues (Terashima et al., J. Biochem. 120 (1996) 1209-1215). In the present work, we examined fibronectin as an extracellular target protein of the released transferase. Fibronectin was ADP-ribosylated by purified transferase and stoichiometry of ADP-ribose incorporation into fibronectin was 1.0 mol/mol of fibronectin. Cell adhesion and spreading assays revealed that ADP-ribosylation of fibronectin markedly inhibited the adhesion activity of fibronectin. A proteolytic peptide map of ADP-ribosylated fibronectin demonstrated that the modification occurs in the cell binding domain of fibronectin. ADP-ribosylation of the RGD peptide suggests that the RGD sequence is the modification site in the domain. ADP-ribosylation of fibronectin in plasma means that fibronectin can probably serve as the substrate for extracellularly released ADP-ribosyltransferase in vivo. Thus, in the extracellular space, ADP-ribosyltransferase released from polymorphonuclear leukocytes may perhaps be involved in regulation of cell adhesion process by interfering with the activity of fibronectin.

ADP Ribose Transferases↗
PubMed1994

Food deprivation protects the rat striatum against hypoxia-ischemia despite high extracellular glutamate.

In a model that combines hypoxia with ischemia, the relationship between histological outcome, evoked rise in blood glucose, and striatal glutamate release was investigated in the 24-h food-deprived and normally fed rat. Food deprivation protected the dorsolateral striatum very effectively, as was shown with a silver stain. An online monitoring technique based on microdialysis showed that, in the protected condition, more glutamate was released into the striatal extracellular space than in the compromised condition. The possibility that the microdialysis results were influenced by a difference in shrinking of the extracellular space following food deprivation was excluded by the measurements of whole-tissue impedance. During the hypoxic-ischemic challenge, blood glucose rose in normally fed rats, but was suppressed almost completely after food deprivation. These results led us to conclude that, in our model of hypoxia-ischemia, the amount of glutamate released is not related directly to the extent of brain damage, but the increase in blood glucose may determine at least part of the brain damage.

Animals↗
PubMed1984

Transsarcolemmal calcium movements in arterially perfused rabbit right ventricle measured with extracellular calcium-sensitive dyes.

Activation-dependent changes of mean extracellular calcium concentrations were monitored spectrophotometrically in arterially perfused right ventricle of rabbit via extracellular application of the calcium-sensitive absorption dyes, antipyrylazo III and tetramethylmurexide. After rest periods of 3 minutes or longer, 10% of total dye-accessible calcium (300-500 microM) is depleted cumulatively from the extracellular space by four to eight beats at 2 Hz stimulation. During continued stimulation, or during quiescence following a depletion response, mean extracellular calcium concentrations return toward the prestimulatory level in the course of 2-4 minutes. A single stimulation placed 2-30 seconds subsequent to rapid pacing results in a potentiated beat with an accompanying net increment of mean extracellular calcium. Total dye-accessible calcium can increase by at least 4% at such a beat, and depletion responses can be repeated immediately thereafter. During a sequence of such responses, extracellular calcium lost cumulatively during three to five rapid beats is replenished, for the most part, by a single post-stimulatory beat. These results demonstrate that most of the "activator pool" of cellular calcium can turn over to the extracellular space during a single contraction cycle in rabbit myocardium, and suggest that, in mammalian myocardium, diastolic calcium efflux may be quantitatively negligible in relation to efflux during excitation-contraction coupling.

Animals↗
PubMed1975

Intercellular junctions in podocytes of the nephrotic glomerulus as seen with freeze-fracture.

The glomeruli of rats rendered nephrotic by administration of aminonucleoside of puromycin were studied with the freeze-fracture technique. The alterations of the podocytes consisted of a progressive blunting of the foot processes and of the disappearance of the extracellular space normally present between the foot processes at the level of the slit pore. In parallel with the closure of the extracellular space, fracture faces of the plasma membrane of the latered podocytes revealed the presence of peculiar membrane differentiations represented mainly by irregular chains of membrane-associated particles in the fracture face A and by variegated grooves in the fracture face B. The presence of grooves in fracture face B indicates that the chains of particles in fracture face A are likely to be tight junctions rather than linear gap junctions. However, since the presence of continuous ridges is exceptional, it is suggested that the tight junctions are the "leaky" -type and that the podocytes many have only limited capacities for assembling junctions of the "tight" -type.

Animals↗
PubMed1976

Kinetics of horseradish peroxidase migration through cerebral cortex.

This study provides a semiquantitative description of the migration of the extracellular space marker, horseradish peroxidase (HRP), through the cerebral cortex. Following a continuous subarachnoid infusion of HRP, this marker was fixed rapidly within the cortical extracellular space (ECS) by intravascular aldehyde perfusion fixation. Microscopic measurements of the maximum depth of penetration of HRP into the cortex perpendicular to the pial surface were taken from coronal whole brain sections of rabbits that had been exposed to HRP for varying periods of time. The depth of penetration plotted as a function of time of exposure to HRP produced a 'diffusion profile'. The failure of experimental points to conform to an ideal diffusion curve indicates that simple diffusion alone is an inadequate explanation of the rate of movement of large molecular solutes from the subarachnoid space through the cerebral cortical ECS. The complex pattern of migration velocity of HRP through cortex may be due to alterations of flux of this solute which result from variations in the volume of ECS in different cortical laminae and to the presence of bulk flow of extracellular fluid in the deeper cortical regions.

Animals↗
PubMed1994

Stromal expression of tenascin is inversely correlated to epithelial differentiation of hormone dependent tissues.

We were previously investigating the expression of the extracellular matrix glycoprotein tenascin in normal and malignant endometrial tissues of humans and rodents. These studies suggested that the expression of tenascin was induced by proliferating epithelia (normal and particularly malignant) and was downregulated with their differentiation. The aim of this study was to investigate the hormone dependency of tenascin expression in (a) the transplantable EnDA endometrial tumor model with or without estrogen deprivation (ovariectomy) of the animals, (b) DMBA-induced rat mammary tumors with or without a hormonal treatment of the animals [ovariectomy, antiestrogen (tamoxifen) or antiprogestin (ZK 98299) treatment] and (c) in the rat prostate of untreated or androgen deprived animals (orchiectomy, flutamide-, casodex- or cyproterone acetate (CPA)-treatment). 1. Estrogen withdrawal by ovariectomy did not affect tenascin expression in transplantable EnDA endometrial adenocarcinoma, meaning the entire extracellular space of the stromal mesenchyme was decorated by tenascin immunoreactivity. 2. In untreated DMBA-induced rat mammary tumors almost the entire extracellular space of the stroma was stained by tenascin immunoreactivity. Ovariectomy and antiestrogen treatment did not affect tenascin expression. In contrast, antiprogestin treatment induced terminal differentiation of mammary tumor cells and in parallel downregulated tenascin expression. 3. In the normal rat prostate no tenascin was detectable by immunocytochemistry. However, following androgen deprivation we found tenascin expression in the stroma of the prostate. The most prominent expression was observable after CPA-treatment, possibly due to its progestagenic potency. In conclusion, the hormones and antihormones tested show no direct effect on the stromal expression of tenascin. However, proliferative activity and a low degree of differentiation of the epithelium induces tenascin expression, whereas epithelial differentiation apparently shuts down tenascin expression. Preliminary in vitro studies suggest that paracrine acting growth factors trigger the hormonal regulation of tenascin expression.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2002

Transepithelial organic anion transport by shark choroid plexus.

Spiny dogfish shark (Squalus acanthias) lateral and IV choroid plexuses (CPs) are ultrastructurally similar to the corresponding tissues of rat. However, shark IV CP is proportionally larger and easily accessible. Moreover, this epithelial sheet can be halved and studied in Ussing flux chambers. We have used confocal fluorescence microscopy and radiotracer techniques to characterize transepithelial transport of the organic anions (OAs) fluorescein (FL) and 2,4-dichlorophenoxyacetic acid (2,4-D), respectively, by shark CP. Lateral and IV CP accumulated 1 microM FL, with highest levels in the underlying extracellular spaces, intermediate levels in epithelial cells, and lowest levels in the medium. 2,4-D and probenecid inhibited FL accumulation in cells and extracellular spaces, suggesting that these substrates compete for common carriers. Unidirectional absorptive [cerebrospinal fluid (CSF)-to-blood] and secretory (blood-to-CSF) fluxes of 10 microM [(14)C]2,4-D were measured under short-circuited conditions in IV CP mounted in Ussing chambers. 2,4-D underwent net absorption, with an average flux ratio of 7. Probenecid, 2,4,5-trichlorophenoxyacetic acid, and 5-hydroxyindolacetic acid reduced net absorption, reversibly inhibiting unidirectional absorption, with no effect on secretion. Ouabain irreversibly reduced net 2,4-D absorption and cellular and extracellular accumulation of FL, suggesting energetic coupling of OA absorption to Na(+) transport. Collectively, these data indicate that shark CP actively removes OAs from CSF by a process that is specific and active.

2,4-Dichlorophenoxyacetic Acid↗