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At least 613 records · Page 34Linked to original sources
PubMed1996

Cytosolic phospholipase A2 (cPLA2) immunoreactivity is elevated in Alzheimer's disease brain.

Phospholipase A2 (PLA2) is the key enzyme that initiates the arachidonic acid cascade, which leads to the generation of multiple eicosanoid products. Many of these products are believed to play an important role in the inflammatory process. Activation of PLA2 is observed under pathological conditions where inflammation is present. Cytosolic PLA2 (cPLA2) is activated by very low levels of calcium and is thought to control receptor-mediated eicosanoid production and to participate in intracellular signal transduction processes. In view of the presence of numerous inflammatory mediators and acute phase proteins in the Alzheimer's disease (AD) brain, localization of cPLA2 in AD brain was evaluated and compared to that observed in nonneurologically diseased controls. In this study, a monoclonal antibody raised against cPLA2 was used to immunostain tissue sections of human cerebral cortex. Five AD cases and six neurologically normal cases were evaluated in the occipital cortex and the cerebellum. Two of the AD cases were also examined in other cortical regions. Granular-like staining with anti-cPLA2 was found to be associated with astrocytes in the cortex of both control and AD cases. Colocalization with GFAP confirmed that cPLA2 immunoreactivity is associated almost exclusively with protoplasmic astrocytes. Staining was abolished when sections were labeled with antibody that had been preadsorbed with purified cPLA2. In AD brain, cPLA2 immunoreactive astrocytes were greater in number and more intensely stained than those in control cases. cPLA2 immunoreactivity was virtually absent in the cerebelium of AD and control cases, despite the presence in this region of diffuse amyloid in two AD cases and amyloid angiopathy in a third case. In the cortex, cPLA2 immunoreactive astrocytes were detected in regions that contained numerous A beta deposits. The finding of elevated levels of cPLA2 immunoreactivity in AD brain supports the hypothesis that there is an active inflammatory process occurring in AD.

Adult↗
PubMed1999

Beijerinck's contribution to the virus concept--an introduction.

The existence of viruses was first recognized when certain pathogens were found to pass through filters that otherwise stop bacteria. Pasteur made such observations in 1887 with the pathogen of rabies, but he thought that the pathogen was a very subtle microbe. In 1886 Adolf Mayer studied the mosaic disease of tobacco plants. He was unable to observe the least trace of a microbe, but still assumed that the pathogen was a bacterium. In 1892 Iwanovsky demonstrated that tobacco mosaic was caused by an agent that passed through bacteria-proof filters but he insisted till the end of his life that the tobacco mosaic virus was a small bacterium. Similar observations were made by Loeffler and Frosch in 1898 on foot-and-mouth disease of cattle. Beijcrinck confirmed the filterability of tobacco mosaic virus but confirmed its properties in more detail and then, in 1898, firmly concluded that tobacco mosaic virus is not a microbe but a contagium vivum fluidum. His idea that a pathogen can be a soluble molecule that proliferates when it is part of the protoplasm of a living cell was revolutionary and new. This new concept has laid the foundation of virus research and directed further studies on the nature of viruses.

Animals↗
PubMed1996

Clinical and laboratory evidence of the importance of the tick D. marginatus as a vector of B. burgdorferi in some areas of sporadic Lyme disease in Bulgaria.

56 adult ticks D. marginatus and 38 adult ticks H. punctata were sampled by the flagging method, transferred to the laboratory, dissected and tested for infection with Lyme disease spirochetes. 3 (7.9%) of the adult H. punctata and 2 (3.57%) of the adult D. marginatus were infected with B. burgdorferi (Bb). This report also presents the case of a patient, who developed Lyme disease symptoms after he had been bitten by a D. marginatus tick. The clinical diagnosis was confirmed by serological testing and by a biopsy, taken from the patient's skin lesion. The skin biopsy was examined under an electron microscope and Bb was found in the sections of the deeper strata of the dermis in two structural forms: (a) cylindrical bodies (protoplasm cylinder) with circular ends covered with a three-layered membrane; (b) granules, situated among the collagenous fibres either closely adhered to them or covered with a membrane. The result of the study demonstrates that in single cases in some ecosystems, ticks D. marginatus might be implicated in Bb transmission to humans as secondary vectors.

Adult↗
PubMed1991

The epidemiology of headache among children with brain tumor. Headache in children with brain tumors. The Childhood Brain Tumor Consortium.

In this report we present aspects of the epidemiology of headache (i.e., pain in the head, face, ear, or neck) among children with brain tumors. The data are derived from the 3,291 subjects in the Childhood Brain Tumor Consortium databank. Overall, 62% of the children with brain tumors experienced chronic or frequent headaches prior to their first hospitalization: 58% of children with supratentorial tumors and 70% of children with infratentorial tumors. The relative frequency of headache increased through age 7 and then leveled off regardless of tumor location. For children under age 5, headache rarely had a duration of more than 1 year prior to hospitalization. Among children over age 4, headache duration of at least one year was significantly greater for supratentorial than for infratentorial tumors. Children with a brain tumor and headache had a different distribution of symptoms and neurologic signs than those without headache. Tumor location and headache status were interactively associated with the presence of other symptoms and neurologic signs. Children with headache had a greater number of other symptoms and neurologic signs. Regardless of tumor location among children with headache, nausea or vomiting, papilledema, and hypoactive tendon reflexes were more frequent, while upper extremity weakness, optic atrophy, and irritability were less frequent. Diplopia, coma, stiff neck, anesthesia or hypesthesia, pupillary abnormalities, and abnormalities of personality, academic performance, or speech were associated with headache in children with supratentorial tumors. No specific symptoms or neurologic signs were associated with headache in children with infratentorial tumors. Supratentorial craniopharyngioma, ependymoma, and protoplasmic astrocytoma were associated with significantly high rates of headache as was infratentorial pilocytic astrocytoma.

Adolescent↗
PubMed1983

Growth, morphology, and serial transplantation of anaplastic human gliomas in athymic mice.

Sixteen of 17 anaplastic human gliomas (AHGs) transplanted into athymic mice produced progressively growing subcutaneous nodules at the site of implantation. Thirty-four of 68 animals (50%) receiving transplanted tissue developed 500 m3 tumors in 24 to 364 days. Fourteen AHG were passed to a second animal generation, and 11 showed continued growth. Eight of these were serially passed, with one reaching a sixth animal generation, four reaching a fifth, and a three third. Once growth occurred in a second animal generation, no AHGs were lost in subsequent passages because of failure to grow. Of 234 animals receiving tumors beyond the first animal generation, 189 (80.8%) developed tumors. Average doubling times of the exponentially growing tumors in serial passage ranged from 3.0 to 19.1 days. This growth rate tended to increase and stabilize in early animal passages. The tumors growing in animals contained cell types which were present in the original human tumors, including fibrillary and protoplasmic astrocytes, small anaplastic cells, gemistocytes, anaplastic spindle cells, and multinucleate giant cells. Glial fibrillary acidic protein (GFAP) was detected in 15 of 17 biopsy specimens and in 12 of 14 AHGs in animals. These data illustrate the value of the athymic mouse system for the investigation of human brain tumors by demonstrating a high rate of successful transplantation, quantitative growth data on serially passed tumors, and morphological and immunochemical resemblance of the tumors in mice to the original human tumors.

Animals↗
PubMed1993

Distribution of taurine-like immunoreactivity in the mouse liver during ontogeny and after carbon tetrachloride or phenobarbital intoxication.

The ontogenic pattern of development of taurine-like immunoreactivity (TLI) was studied in the mouse liver. The effect on adult mice of carbon tetrachloride or phenobarbital treatment was also examined. Light-microscopically, granules of TLI were first found in the liver from 17-day-old embryos, diffusely distributed throughout the lobules. These positive granules increased with age, were most numerous in the two-week-old mouse, and were notably decreased in the central region of some lobules in the three-week-old mouse. In mature mice, hepatocytes containing TLI-positive granules were distributed unevenly in each liver lobule, and were located predominantly in the peripheral region. Electron-microscopically, TLI was observed in small vesicles in the cytoplasm of hepatocytes and was found mainly in the cisternal lumen of smooth-surfaced endoplasmic reticulum. Some taurine-positive vesicles surrounding the reticulum seemed to associate with the protoplasm. Similar positive vesicles were often located near the bile canaliculi. In carbon tetrachloride-intoxicated mature mice, TLI was no longer limited to the peripheral region of lobules; hepatocytes situated in the central region of lobules also contained intense TLI. In mice injected with a small and repeated dose of phenobarbital, the distribution pattern of TLI was similar to that in the untreated group. However, in mice injected with a large dose of phenobarbital, TLI was markedly increased, especially in the central region of lobules. The results demonstrate that the distribution pattern of TLI in mouse liver changes during development, and that the pattern in mature mice is affected by intoxication with carbon tetrachloride or a toxic dose of phenobarbital.

Animals↗
PubMed1992

Epidemiology of seizures in children with brain tumors. The Childhood Brain Tumor Consortium.

We examined potential clinical and pathologic correlates of seizures among the 3,291 children in the Childhood Brain Tumor Consortium database. Fourteen percent had seizures prior to their hospitalization for a brain tumor. Among children who had a supratentorial tumor, seizures occurred in 22% of those less than 14 years of age. The prevalence of seizures increased to 68% of older teenagers. Among children with an infratentorial tumor, the prevalence of seizures was relatively constant at 6% over all age groups. The onset of seizures began more than one year prior to surgical tumor removal in over half of the children aged five or more with supratentorial tumors, significantly longer than for those of the same age with infratentorial tumors. Almost all children (98.9%) with an infratentorial tumor and seizures had at least one other symptom and more than three-fourths of them had at least three. Eighty-nine percent of children with a supratentorial tumor and seizures had at least one other symptom and more than one-half had at least three symptoms. Regardless of whether the tumor was above or below the tentorium, confusion or stupor and coma were more common in children with seizures than in children without seizures. Among children with supratentorial tumors, symptoms of a declining academic performance or an abnormality of personality, speech, walking, or sensation were significantly more frequent in children with seizures, while visual symptoms (other than visual loss or diplopia) and nausea or vomiting were less frequent. Among children with supratentorial tumors, those who had seizures were more likely to have paralysis of an arm, hand, or face, confusion or stupor, or coma and less likely to exhibit irritability, papilledema, optic atrophy, decreased visual acuity, pupillary abnormalities, or abducens paresis. Among children with infratentorial tumors, those with seizures were significantly less likely to have truncal ataxia, but more likely to experience confusion, stupor, or coma. In the supratentorial compartment, astrocytoma (nos), protoplasmic astrocytoma, anaplastic astrocytoma, and ependymoma were more frequently associated with seizures than was craniopharyngioma. No infratentorial tumor type was more or less likely to be associated with seizures. All common tumor types that were represented in both the supratentorial and the infratentorial compartment except astrocytoma (nos) were associated with significantly greater rates of seizures when located in the supratentorial compartment. The tumor location with the highest incidence of seizures was, as expected, the superficial cerebrum. More than 40% of the children with such tumors had seizures.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1989

Intraobserver reproducibility in assigning brain tumors to classes in the World Health Organization diagnostic scheme. The Childhood Brain Tumor Consortium.

We studied how reproducibly neuropathologists assign childhood brain tumors to World Health Organization (WHO) diagnostic categories using a subsample from the Childhood Brain Tumor Consortium (CBTC) data. Among the 713 cases, 539 (76%) received the same diagnosis on two different readings by the same team of two neuropathologists. Among the 297 tumors in the supratentorial compartment, 201 (68%) received the same diagnosis on both reviews, whereas among the 392 tumors in the infratentorial compartment, 320 (82%) received the same diagnosis. The eight tumor diagnoses that were the most reliable were craniopharyngioma, germinoma, teratoma, medulloblastoma, pilocytic astrocytoma, ependymoma, subependymal giant cell astrocytoma, and choroid plexus papilloma, Px, the conditional probability of agreement given that one of the reviews resulted in specific diagnosis 'X', ranged from 0.97 to 0.75 for these diagnoses. In contrast, Px for 16 other childhood brain tumor diagnostic categories ranged from 0.60 to 0.00. Pilocytic astrocytoma, ependymoma, medulloblastoma, and astrocytoma not otherwise specified (nos) had significantly lower Px values (p less than 0.05) when these tumors were located in the supratentorial compartment than when below the tentorium. Px was not significantly lower for any category when tumors were located in the infratentorial compartment. The array of substituted diagnoses that lowered reproducibility was greater when tumors were located supratentorially. To improve the definitions, eliminate overlapping diagnostic categories, and sharpen the fuzzy boundaries that contribute substantially to limited reproducibility, we suggest: (1) the categories of astrocytoma nos, fibrillary astrocytoma, and protoplasmic astrocytoma be collapsed into a single category of astrocytoma; (2) the diagnostic category of desmoplastic medulloblastoma be combined with medulloblastoma; and (3) the criteria for anaplasia should be further refined to include quantification of critical histologic features, e.g., agreed upon operational definitions for amount of cell density, number of mitoses and pleomorphism for anaplastic astrocytoma and anaplastic ependymoma.

Brain Neoplasms↗
PubMed1992

The carbohydrate epitope 3-fucosyl-N-acetyllactosamine is developmentally regulated in the human cerebellum.

The carbohydrate epitope 3-fucosyl-N-acetyl-lactosamine (CD15) is involved, as a constituent of glycoconjugates, in cell-cell interactions and cell sorting during rodent CNS morphogenesis. The present study was designed to test whether CD15 is also involved in the development of the human CNS. Human cerebellar hemispheres and vermes from the 24th week of gestation (wg) to the 26th postnatal month (pnm) and from adults were investigated for CD15 immunoreactivity, using the monoclonal antibody MMA. Our findings establish that the carbohydrate moiety is developmentally regulated in neuronal and glial cells during their differentiation. First, the parallel fibers of granule cells are CD15+ during the epoch of synaptogenesis with Purkinje cell dendrites. Second, a subpopulation of neurons from the dentate nucleus is transiently CD15+ from the 32nd wg until the 15th pnm. Third, at the onset of myelination (around the 35th wg), CD15 immunoreactivity is discernible in the cytoplasm of young oligodendrocytes. Immunoreactivity on protoplasmic astrocytes of the inner granular layer and on fibrous astrocytes of the white matter progressively increases during fetal development. In addition, the CD15 epitope is persistently present on Bergmann glial processes and ependymal cells. Within the three subdivisions of the cerebellum, i.e., hemispheres, vermis, and flocculonodular lobe, the CD15 expression follows a different timing of morphogenesis. For example, diminution of immunoreactivity in the parallel fibers occurs first in the phylogenetically older flocculonodular lobe and vermis, and later in the phylogenetically younger hemispheres. This study shows that in the human cerebellum the distribution of CD15 undergoes marked developmental changes. This epitope may also act in cell-to-cell recognition, and perhaps could play a role in controlling CNS development.

Adult↗
PubMed1982

Unorthodox pattern of microvilli and intercellular junctions in regular retinular cells of the porcellanid crab Petrolisthes.

1. Retinular fine structures in compound eyes of the porcellanid crab Petrolisthes differs significantly from two paguroid anomurans Clibanarius and Pagurus which basically conform to the usual conservative decapod crustacean retinular pattern. 2. Bidirectional orientation of microvilli has been discovered in rhabdomeres of retinular cells R1-R7 in Petrolisthes. Distally the regular rhabdom has mainly a typical banded microvillus structure (Figs. 7,8). Proximally rhabdom banding continues but uniquely all seven regular retinular cells contribute sets of alternately orthogonal microvilli to each band (Figs. 5, 6, 12). This unorthodox pattern should reduce polarization sensitivity and enhance sensitivity to unpolarized light. 3. In this special region microvillus layers are strongly elliptical in cross section with the minor axis parallel to the microvilli (Fig. 12). Hence the ends of the major axes protrude considerably from the central area of overlap (Fig. 6). 4. Retinular cell eight has bidirectional microvilli (Figs. 5-7) as usual in brachyuran crabs. Unlike the latter as well as paguroid crabs, Petrolisthes has square facets and a rectangular retinular array (Figs. 1, 3) similar to other galatheids and macruran decapods generally. It also resembles macrurans (shrimps and lobsters) in having perirhabdomal vacuoles absent or much reduced. 5. Tight junctions occur widely between adjacent retinular cells (Figs. 14, 17) especially basally immediately distal to longitudinal zonular adherentes (Figs. 6, 16) typical of compound eyes. Freeze fracture reveals in addition numerous rectangular arrays of particles on the protoplasmic face of retinular cell membrance near, but not part of, the rhabdom (Figs. 19, 20). Other authors have hypothesized polarized transfer functions for similar particle aggregates in certain vertebrate cells.

Animals↗
PubMed1986

Differential immunocytochemical staining for glial fibrillary acidic (GFA) protein, S-100 protein and glutamine synthetase in the rat subcommissural organ, nonspecialized ventricular ependyma and adjacent neuropil.

Antibodies raised against glial fibrillary acidic protein (GFA), S-100 protein (S100) and glutamine synthetase (GS) are currently used as glial markers. The distribution of GFA, S100 and GS in the ependyma of the rat subcommissural organ (SCO), as well as in the adjacent nonspecialized ventricular ependyma and neuropil of the periaqueductal grey matter, was studied by use of the immunocytochemical peroxidase-antiperoxidase technique. In the neuropil, GFA, S100 and GS were found in glial elements, i.e., in fibrous (GFA, S100) and protoplasmic astrocytes (S100, GS). The presence of S100 in the majority of the ventricular ependymal cells and tanycytes, and the presence of GFA in a limited number of ventricular ependymal cells and tanycytes confirm the glial nature of these cells. The absence of S100, GFA and GS from the ependymocytes of the SCO, which are considered to be modified ependymal cells, suggests either a non-astrocytic lineage of these cells or an extreme specialization of the SCO-cells as glycoprotein-synthesizing and secreting elements, a process that may have led to the disappearance of the glial markers.

Animals↗
PubMed1987

Demonstration of rod and cone photoreceptors in the lamprey retina by freeze-replication and immunofluorescence.

In common with other cyclostomata, the Japanese river lamprey (Lampetra japonica) has a retina consisting of distinct types of photoreceptor cells called long and short photoreceptor cells. After freeze-fracture, disc membranes of these photoreceptor cells were characterized in common by a homogeneous distribution of intramembrane particles on the protoplasmic fracture faces, in contrast to those of the myeloid bodies bearing scattering particles. Immunofluorescent examination was applied to the retina with monoclonal antibodies raised against bovine and chicken rhodopsins. Positive immunoreactivity was found to be limited to outer segments of the short cell, leaving the entire body of the long cell and all other components of the retina negative. The results suggest that the short cell is more closely related to a rod-type photoreceptor cell characterized by rhodopsin as its visual pigment.

Animals↗
PubMed1976

Freeze-etch and histochemical evidence for cycling in crayfish photoreceptor membranes.

Freeze-etched rhabdoms and adjacent cytoplasmic cytoplasmic organelles from crayfish compound eyes have been studied for evidence of photoreceptor membrane cycling. The protoplasmic leaflet face (PF) of split photoreceptor membrane of the microvilli is richly particulate. The particles (92 +/- 16 A in diameter in surface fractures; 70 +/- 9 A in cross fractures; density about 8000/mum2) probably indicate rhodopsin molecule localization. Closely similar particles appear in membranes of pinocytotic vesicles, multivesicular bodies (MVB) and secondary lysosomes. In contrast other retinular cell membranes like plasma membrane remote from the rhabdom are quite distinct (60 +/- 23 A particle diameter, density ca 1000/mum2.) Histochemical tests for acid phosphatase demonstrate its presence in well-developed (but not early stage) MVBs, mixed lamellar vesicular bodies (LVB) and lamellar bodies. Density of PF particles decreases from 8000 in MVB to roughly 4500/mum2 in LVB indicating a degradative sequence from rhabdom to lamellar bodies. Membrane leaflet orientations show that primary endocytosis from microvilli must be followed by secondary endocytosis of fused coated vesicles to form MVB. Morphological evidence for photoreceptor membrane resynthesis has not been found yet in crayfish but some has been obtained in other crustaceans.

Acid Phosphatase↗
PubMed1986

Organization of filaments underneath the plasma membrane of developing chicken skeletal muscle cells in vitro revealed by the freeze-dry and rotary replica method.

Cytoskeletal organization and its association with plasma membranes in embryonic chick skeletal muscle cells in vitro was studied by the freeze-drying and rotary-shadowing method of physically ruptured cells. The cytoskeletal filaments underlying the plasma membranes were sparse in myogenic cells at the stage when cells exhibited great lipid fluidity in plasma membranes (fusion competent mononucleated myoblasts and recently fused young myotubes). Myotubes at more advanced stages of development possessed a highly interconnected dense filamentous network just underneath the cell membrane. This subsarcolemmal network was composed predominantly of 8-10 nm filaments; they were identified as actin filaments because of their decoration with myosin subfragment-1. Fine fibrils having a diameter of 3-5 nm were found on the protoplasmic surface of the plasmalemma at both the early and advanced stages of development. They were associated with the subsarcolemmal cytoskeletal filaments. Short 2-5 nm cross-linking filaments were occasionally seen between filaments in the subsarcolemmal network. We conclude that, although the subsarcolemmal cytoskeletal network contains many actin filaments, this domain appears to play some role in preserving the cell shape in the form of the membrane skeleton rather than membrane mobility.

Aging↗
PubMed1978

Distribution of myosin and the glial fibrillary acidic protein (GFA protein) in rat spinal cord and in the human frontal cortex as revealed by immunofluorescence microscopy.

The glial fibrillary acidic (GFA) protein and myosin were localized in rat spinal cord and human frontal cortex using specific antibodies against GFA protein from human spinal cord and highly purified smooth myosin from chicken gizzard by means of an indirect immunofluorescence microscopical approach. A strong GFA protein and myosin immunoreactivity was found in astrocytes of the white and grey matter and in the external glial limitans membrane. The very fine branches of astrocytic processes stained with anti-GFA protein, but not with anti-myosin. Similar results were obtained with the human frontal cortex, where myosin antibodies failed to reveal the very fine branches of protoplasmic astrocytes. As a whole, staining with the GFA protein antiserum was more crisp than with the myosin antibody.

Animals↗
PubMed1989

Innervation and gap junctions of intestinal striated and smooth muscle cells in the loach. Thin section and freeze-fracture study.

The tunica muscularis of the proximal intestine of the loach consisted of intermingling striated and smooth muscle cells without forming any distinct sublayers. Close contacts devoid of intervention by a basal lamina sometimes occurred between these different types of muscle cells. Gap junctions were occasionally found between heterologous as well as homologous muscle cells. In freeze-fracture replicas, striated muscle cells were distinguished from smooth muscle cells by numerous, evenly distributed subsurface caveolae. These were relatively rare and linearly arranged in smooth muscle cells. Variously-sized and -formed aggregations of connexon particles were found in the protoplasmic fracture-face of both muscle cells. Striated muscle cells had aggregates of connexon particles taking the form of either a small solid polygon or an annulus with a particle-free central region. In smooth muscle cells, the particles were arranged either in variously-sized patches or in straight lines. Topologically, heterologous gap junctions observed in ultrathin section were thought to correspond to the small patchy aggregations. Striated muscle cells in the gut had neuromuscular junctions, which differed morphologically from "cholinergic" nerve terminals at neuromuscular junctions of typical skeletal muscle cells. The smooth muscle cells had close apposition with axonal terminals containing many granular vesicles and a variable number of small, clear vesicles. Occasionally, a "cholinergic"-type axonal terminal with a presynaptic active site was found close to a smooth muscle cell.

Animals↗
PubMed1976

Cycling aggregation patterns of cytoplasmic F-actin coordinated with oscillating tension force generation.

Isometric contracting protoplasmic veins of Physarum polycephalum show cycling patterns of cytoplasmic F-actin, dependent on their oscillating contraction behaviour (minute rhythms). The process of fibrillogenesis represents a parallel arrangement of F-actin chains ("plasma filaments, microfilaments") during the isometric contraction phase. A part of the results of the present work corroborates previous results on stretch-activated veins which showed that the fibrillar form of F-actin reflects the isometric contracted state. During isometric relaxation phase, a disaggregation of the fibrillar pattern takes place and is accompanied by a deparallelisation of F-actin chains. Therefore, the isometric relaxed state of cytoplasmic actomyosin is non-fibrillar in nature. Thus, the morphologically detectable fibrillar form of cytoplasmic actomyosin, according to physiological interpretation, is solely representative of the isometric contracted state. The question whether assembly-disassembly processes, e.g. G equilibrium F-actin-transformation, play a role in the contraction-relaxation cycle is discussed.

Actins↗
PubMed1979

Cytochemistry and freeze-fracture of membranes isolated from the electrocyte of Electrophorus electricus (L.).

Membranes were isolated from the main electric organ of Electrophorus electricus and studied by means of cytochemistry and freeze-fracture. The membrane fractions consisted of vesicles inside-in as determined by localization of anionic sites using colloidal iron and cationized ferritin particles. The anionic sites were not homogeneously distributed on the surface of the vesicle. Freeze-fracture showed the presence of intramembranous particles associated with either protoplasmic (P) or extracellular (E) faces of the membrane. Regions of the membrane without particles were observed. The results are discussed in relation to the existence of association between intramembranous particles and membrane receptors.

Animals↗