bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of glutaraldehyde and formaldehyde fixation on the retention and subcellular location of [3H]5-hydroxytryptamine in rabbit platelets: A study using liquid scintillation counting and E.M. autoradiography
Authors: Baker J. R. J. , Pay G. F. 
Published: April 2021

ABSTRACT
The retention and loss of [3H]5-hydroxytryptamine (5-HT) from rabbit platelets during fixation was studied using liquid scintillation counting and quantitative electron-microscopic autoradiography. The results were at variance with previously reported data on human platelets. Following treatment of the platelets with either 2·0% formaldehyde or 2·5% glutaraldehyde for 2 min or 1 h it was found that a significantly increased proportion of the radioactivity was lost from treated as compared with untreated platelets. Using a method of analysis which accounts for cross-scatter of decay particles between cell compartments, electron-microscopic autoradiography revealed that 50 % of the radioactivity following incubation of platelets with [3H]5-HT was associated with dense bodies and 30 % in the cytoplasm when fixation was in formaldehyde or glutaraldehyde. The only major difference in the labelling pattern was that whereas glutaraldehyde appeared to retain no activity in the surface connected system the latter contained 12 % of total retained activity following fixation with formaldehyde.
Light-induced pigment aggregation in cultured fish melanophores: spectral sensitivity and inhibitory effects of theophylline and cyclic adenosine-3′,5′-monophosphate
Authors: Wakamatsu Yuko , Kawamura Satoru , Yoshizawa Toru 
Published: April 2021

ABSTRACT
About 20 % of xiphophorin fish (Xiphophorus maculatus) dermal melanophores which were cultured in monolayer for 5 to 10 days responded to light directly, exhibiting reversible melanosome aggregation within a few minutes. In order to determine the spectral sensitivity for the light-response, absorbance changes due to the light-induced melanosome aggregation were measured on single melanophores in a range of wavelengths from 370 to 550 nm using a recording microspectrophotometer. The melanophores showed maximum sensitivity to a wavelength of about 410 nm and very little to those longer than 500 nm. 10−4 to 10−2 M theophylline and 10−4 M cAMP had inhibitory effects on the light-response.
Electron-microscope study of Dictyostelium discoideum plasma membrane and its modifications during and after phagocytosis
Authors: Ryter Antoinette , Hellio Raymond 
Published: April 2021

ABSTRACT
The study of plasma membrane and phagosome membrane of Dictyostelium discoideum was performed using 2 lectins: concanavalin A (Con A) and Wheat Germ Agglutinin (WGA), and 2 markers of anionic sites: colloidal iron hydroxide (CIH) and cationized ferritin (CF).
These labellings were applied to fixed partially broken cells, which had ingested a large quantity of yeast. They showed that Con A and CF labelled both the outer and inner faces of the plasma membrane, whereas CIH and WGA were deposited on the outer face only. Phagosome membranes displayed the same location as the plasma membrane for Con A, CF and CIH even in very old phagosomes. This suggests that most receptors of these 3 markers were not degraded by hydrolases. In contrast, phagosome membranes of young and old phagosomes did not react with WGA. When labellings were made on yeast phagocytozing cells, the membrane of phagocytic cups was also devoid of WGA, while it was labelled with the 3 other markers. The absence of WGA labelling was not observed during ingestion of bacteria and latex beads, suggesting a specific relationship existed between yeast cells and WGA receptors.
Cell surface localization of 5′AMP nucleotidase in prestalk cells of Dictyostelium discoideum
Authors: Armant D. Randall , Stetler David A. , Rutherford Charles L. 
Published: April 2021

ABSTRACT
5’AMP nucleotidase activity was localized by electron microscopy in Dictyostelium discoideum during cell differentiation. In addition, the activity was assayed by micro enzymic methods in sections dissected from specific cellular regions of lyophilized individuals. The results of the 2 procedures were in agreement, demonstrating that at the culmination stage of development the activity is strikingly localized in the prestalk cells adjacent to the prespore region. The cytochemically stained reaction product appeared only along the plasma membrane of the cells. As prestalk cells migrate into the stalk sheath and undergo differentiation, the activity is rapidly lost. Examination of stained cells at high magnification revealed the product accumulation to be primarily at the cell surface, suggesting that the enzyme functions extracellularly. Occasionally, cells having the morphological appearance of prestalk cells were found within the prespore region. These cells demonstrated 5’AMP nucleotidase activity at their plasma membrane in sharp contrast with neighbouring prespore cells. The strategic localization of 5’AMP nucleotidase may reflect a mechanism for establishing and maintaining regulatory levels of extracellular 5’AMP and/or adenosine during pattern formation in this model system.
Distribution of actively absorbed diffusible sugars in the jejunal epithelium of the rat
Authors: Johnson I. T. , Bronk J. R. 
Published: April 2021

ABSTRACT
Electron-microscope autoradiography, using freeze-dried frozen sections of unfixed tissue, was used to study the distribution of actively transported materials in the jejunal epithelium of the rat in vitro. After a few minutes incubation, the grain density over the organelle-packed interiors of the apical cytoplasm of the columnar absorptive cells was significantly greater than that over the structureless peripheral cytoplasm. This difference in the relative specific activities of the 2 subcellular compartments increased during accumulation of labelled galactose, and decreased as preloaded galactose was washed out of the epithelium. A similar compartmentation was observed in vascularly perfused intestines exposed to labelled galactose from either the mucosal or the serosal sides. These observations suggest the presence of an intracellular mechanism controlling the location and concentration of transported substrates during intestinal absorption.
Pronuclei of heliophrya erhardi matthes during conjugation and their differential association with coated and uncoated microtubules
Authors: Lanners H. Norbert 
Published: April 2021

ABSTRACT
Microtubules surrounding the pronuclei during conjugation of the suctorian ciliate Helio-phrya erhardi can be divided into 2 distinct classes by electron microscopy. Microtubules around the stationary nucleus have a conventional appearance and presumably serve as a skeleton, anchoring that nucleus in its cytoplasmic position. Microtubules surrounding the prospective migratory nucleus are coated with electron-dense material and are in some cases associated with 7-nm filaments. These coated microtubules supposedly function to transport the migratory nucleus into the conjugation partner.
The mode of action of 2,4-D in counter-acting the elongation of carrot cells grown in culture
Authors: Lloyd Clive W. , Lowe Susan B. , Peace Geoffrey W. 
Published: April 2021

ABSTRACT
The growth regulator 2,4-D (2,4-dichlorophenoxyacetic acid) has been used to investigate the inter-relationship between cell elongation and cell division in carrot suspension cells. Maintained in 1 mg/1. 2,4-D, dividing populations of cells remain spheroidal and in clusters. But when subcultured into lower levels or zero, 2,4-D they increasingly elongate at the expense of division. Over the range of 0 to 1·0 mg/1. 2,4-D, elongation and division are therefore inversely related. However, by suppressing the mitogenic effect with FUdR it can be shown that cells do elongate in 1 mg/1. 2,4-D–a concentration which otherwise produces dividing, spheroidal cells. This indicates that mitogenic levels of 2,4-D do not perturb structures which support cellular elongation. This conclusion is confirmed by immuno- and electron-microscopy which show that development of elaborate arrays of cytoplasmic microtubules is unaffected by 1 mg/1. 2,4-D when FUdR is present. It is concluded that over the time periods under study here, 2,4-D regulates cell size (and shape) by stimulating growing cells to enter the division cycle and not by inhibiting elongation per se.
Comparative ultrastructure of eyespot membranes in gametes and zoospores of the green algaUlva lactuca(ulvales)
Authors: Robenek H. , Melkonian M. 
Published: April 2021

ABSTRACTEyespot membranes in zoospores, and male and female gametes of the green alga Ulua lactuca, were studied comparatively by the freeze-fracture technique. The plasmalemma and the outer chloroplast envelope membrane overlying the eyespot lipid globules are specialized in all 3 types of reproductive cells. In the eyespot region the protoplasmic face (PF) of the outer chloroplast envelope membrane contains significantly more intramembraneous particles (IMP) compared to membrane areas outside the eyespot: in female gametes there are 2·5 times more IMP/μms, in zoospores 3 and in male gametes about 4. Small size-class IMP (4–6 nm diameter) are particularly abundant on both fracture faces of the outer chloroplast membrane, but size-class distribution is not significantly different between membrane areas inside and outside the eyespot region. The total number of IMP/eyespot on the PF of the outer chloroplast membrane was calculated to be 4 9 00 in male gametes, 5500 in female gametes and 11 2 00 in zoospores.The results are discussed in accordance with the view that these membrane specializations participate in photoreception relating to green algal phototaxis. Evidence is presented that there is a correlation between IMP numbers per eyespot in the outer chloroplast envelope membrane and the different phototactic behaviour of gametes compared to zoospores in Ulua.
Ultrastructural changes in rat hepatocytes after partial hepatectomy, and comparison with biochemical results
Authors: Murray A. B. , Strecker W. , Silz S. 
Published: April 2021

ABSTRACT
Ultrastructural changes in rat hepatocytes in the first 24 h following partial hepatectomy (p.h.), i.e. in the premitotic phase of liver regeneration, were studied using electron microscopic morphometry. Livers were investigated J, 1,4, 8, 12, 20 and 24 h after p.h. and J, 8, 20 and 24 h after a sham operation. Two effects appear to be associated specifically with the regeneration process: (1) an increase in the volume density of lysosomes to a peak between 4 and 8 h after p.h. ; and (2) a doubling in the number of mitochondria per cell by 24 h without any associated increase in the total mitochondrial volume. Two further changes were observed only after p.h.: (1) a massive accumulation of lipid in the form of lipid droplets by 24 h; and (2) the appearance of ‘protein droplets’ (very large lysosomal-like structures) at various stages. Both these changes appear to be secondary effects associated with the stimulation for, but not necessary to, cell division. The loss of glycogen observed immediately after both p.h. and a sham operation is a non-specific effect probably resulting from operation-induced stress.
The results are discussed with reference to the changes observed in the biochemical composition of blood plasma. Glucagon appears to play an important role in the stimulation of some of the ultrastructural changes observed.
Phosphatidate phosphohydrolase activity as a marker for surfactant synthesis in organotypic cultures of type ii alveolar pneumonocytes
Authors: Douglas William H. J. , Sommers-Smith Sally K. , Johnston John M. 
Published: April 2021

ABSTRACT
The specific activity of phosphatidate phosphohydrolase (PAPase) (EC 3.1.3.4) has been assayed in organotypic cultures of foetal rat lung type II alveolar pneumonocytes and in L2 cells derived from type II cells of the adult rat lung.
This enzyme catalyses a critical step in the synthesis of phosphatidylcholine, the major lipid component of pulmonary surfactant. Surfactant is produced by the mature type II cell in culture as well as in vivo. The specific activity of PAPase in organotypic cultures prepared from foetal rat lung starting at 16 days of gestation increased four-to fivefold during the first 7 days in culture. The specific activity of this enzyme was further increased through the 21 days of culture. In parallel with the increase in PAPase specific activity in the cultures were morphological changes in the type II cells such as the appearance of increased numbers of lamellar bodies. The specific activities of PAPase samples derived from non-type II cell cultures maintained under identical conditions were compared. Organotypic cultures and L2 cells, a culture system that also exhibits type II cell characteristics, show PAPase specific activities five to six times greater than cultures that do not contain type 11 cells. PAPase activity in the type 11 cell cultures parallels the development of mature patterns of pulmonary surfactant synthesis storage and secretion.
Particle arrays on insect nerve membranes
Authors: Flower N. E. , Briers J. D. 
Published: April 2021

ABSTRACT
Freeze-fracture studies of Lepidopteran antennae have revealed the presence of orthogonal arrays of particles on antennal nerve membranes. Initial impressions were that several different arrays were present. Optical diffraction was used to examine the arrays on the electron micrograph negatives. This technique showed that all the arrays were derived from the same basic structure, suggesting that the superficial differences in appearance were due to shadowing effects. The particles are arranged in a lattice with spacings of 10’7 nm × 9·l nm. The arrays are not clear-cut but tend to break up, producing a disorganized region around their edges. The particles are shown to have depressions in them. However, the evidence available suggests that the arrays do not have the other characteristics of gap junctions. The arrays appear not to be present on most of the nerve membrane faces, occurring only in localized regions of the nerve membranes where they are present in large numbers. This suggests that the arrays may have a specialized local function.
Effects of endotoxin treatment on the differentiation of guinea pig megakaryocytes to blood platelets
Authors: Raha S. , Wesemann W. 
Published: April 2021

ABSTRACT
The effect of endotoxin treatment (30μg/kg body weight) on megakaryocyte development and platelet production in guinea pigs was investigated. A moderate thrombocytopenia was noted at 24 h after endotoxin administration. Recovery was observed at 48 h when the platelet count had almost reached the normal level. A significant increase in platelet production was obtained at 48h, indicated by an enhancement in incorporation of labelled sulphate into platelets and also by an increase in the number of circulating heavier platelets. Megakaryocytes were classified into different developmental stages -megakaryoblast, promegakaryocyte, megakaryocyte -using standard morphological criteria (size, shape of nucleus, nucleus/cytoplasm ratio). The number of mature megakaryocytes increased at 24 and 48h after endotoxin treatment. It was possible to distinguish between two different types of mature megakaryocytes— early mature and mature megakaryocytes -by the presence of a methanol-sensitive acid phosphatase. This enzyme is found mainly in mature, presumably platelet-forming, megakaryocytes and in platelets. The increased number of mature megakaryocytes at 24 h was due to an enhancement in the number of early mature megakaryocytes, whereas the change at 48 h was due largely to an increased number of mature, platelet-forming megakaryocytes. Megakaryocytes were isolated from bone marrow of guinea pigs by Percoll densitygradient centrifugation and incubated with radioactively labelled leucine. Compared with the untreated controls megakaryocytes isolated 24 h after endotoxin treatment took up and incorporated higher amounts of leucine into protein, indicating a higher metabolic capacity of the early mature megakaryocytes. No alteration in the ploidy distribution of megakaryocytes was noted after endotoxin treatment.
Vanadate, an inhibitor of growth, development and endocytosis in Dictyostelium discoideum amoebae
Authors: Klein Gérard , Cotter David A. , Martin Jean-Baptiste , Satre Michel 
Published: April 2021

ABSTRACT
Axenic growth of amoebae of the slime mold Dictyostelium discoideum was found to be reversibly inhibited by vanadate. Pinocytosis, when measured with fluorescein-labeled dextran as a fluorescent fluid-phase marker was strongly inhibited by vanadate. Inhibition was observable at vanadate concentrations as low as 0·2 mM. Sucrose entry through pinocytosis induced massive cell vacuolation and this effect was blocked by vanadate. Secretion of soluble lysosomal enzymes is another aspect of membrane traffic in Dictyostelium. Secretion of two typical lysosomal enzymes, acid phosphatase and hexosaminidase, was inhibited by concentrations of vanadate in the same range as for pinocytosis inhibition. Vanadate also prevented the morphogenetic developmental program that follows nutrient starvation. In contrast, vanadate did not prevent heat-induced spore germination. Vanadate had no significant action on the intracellular nucleoside triphosphate level or on the cytosolic pH. It is suggested that the particular effect of vanadate in Dictyostelium is to inhibit the fusion of endosomes with lysosomes. Our results provide a probe that could be useful to clarify the mechanisms of endocytosis.
Induction of dna synthesis by cholera toxin in the temperature-sensitive cell-cycle mutants of rat 3Y1 fibroblasts at a restrictive temperature
Authors: Kabemura Mayumi , Shimura Hideo , Matsuzaki Akinobu , Ohtsu Masumi , Kimura Genki 
Published: April 2021

ABSTRACT
Four temperature-sensitive mutants of rat 3Y1 fibroblasts representing separate complementation groups (3YltsD123, 3YltsF121, 3YltsG125 and 3YltsH203) are arrested at a restrictive temperature of 39-8°C mainly with a G1-phase DNA content (temperature arrest). Cholera toxin (CT) (3μgml−1) induced DNA synthesis at 39·8°C in the temperature-arrested cultures of two mutants (3YltsD123 and 3YltsG125). This effect of CT was not mimicked by other agents known to elevate the cellular level of cyclic AMP, such as dibutyrylcyclic AMP, prostaglandin El and forskolin, suggesting that the elevation of cellular cyclic AMP level per se is not responsible for the induction of DNA synthesis by CT. Addition of the B subunit of CT to the temperature-arrested cultures of 3YltsD123 and 3YltsG125 did not induce DNA synthesis at 39·8°C, indicating that the binding of CT to the cell surface alone is insufficient for the induction. The CT-treated cell membrane fraction prepared from temperature-arrested 3YltsG125 cells had similar activity for [32P]ADP-ribosylation of the 45 ×103Mr protein to that prepared from cells proliferating at a permissive temperature of 33·8°C. All these results suggest that 3YltsG125 cells utilize a CT-responsive signal transduction pathway, different from adenylate cyclase cascade, for preparation for entry into S phase in the temperature-arrested 3YltsG125. A pertussis toxin-sensitive substrate seems to be involved in the pathway, because pertussis toxin suppressed the induction of DNA synthesis by CT at 39-8°C in 3YltsG125. Neither H-7 (inhibitor of protein kinase C) nor W-7 (inhibitor of calmodulin) influenced the DNA synthesis induced at 39·8°C by CT in 3YltsG125, suggesting that the pathways involving protein kinase C or calmodulin are not responsible for the process.
A mycoplasmal protein influences tumour cell invasiveness and contact inhibition in vitro
Authors: Schmidhauser Christian , Dudler Robert , Schmidt Thomas , Parish Roger W. 
Published: April 2021

ABSTRACT
Fab fragments of a monoclonal antibody directed against p37, a protein associated with the surface of FS9 mouse sarcoma cells, were previously found to inhibit the highly invasive behaviour of FS9 cells in vitro. We show that p37 originates from Mycoplasma hyorhinis. Infecting various cell lines with the mycoplasma consistently increased their invasiveness when confronted with chicken heart fibroblasts using Abercrombie’s confronted explant technique. Conversely, removing the mycoplasmas or blocking p37 with specific Fab fragments reduced invasiveness. Analysis of individual cell collisions using time-lapse filming showed that the addition of Fab fragments to cells infected with M. hyorhinis greatly increased the level of contact inhibition. The antibody also reduced the invasiveness of transformed cells that did not express the p37 antigen. Hence, a cellular protein or proteins that are structurally related to p37 apparently influence invasive behaviour.
Adipocytic cells cultured from marrow have osteogenic potential
Authors: Bennett J. H. , Joyner C. J. , Triffitt J. T. , Owen M. E. 
Published: April 2021

ABSTRACT
Stromal colonies with fibroblastic morphology grow from rabbit marrow cells in culture supplemented with foetal calf serum. In this study the same marrow cells cultured with autologous rabbit plasma and hydrocortisone form colonies of a single lineage that express the adipocytic phenotype. A comparison of the potential for differentiation of cloned cell populations grown from fibroblastic and adipocytic colonies has been made using an in vivo diffusion chamber assay. The adipocytic colonies differentiated and grew to a limited size in medium with rabbit plasma and hydrocortisone, but attempts to isolate them and expand them in this medium failed. When the serum supplement was changed to foetal calf serum at day 10 the cells in the adipocytic colonies acquired a less differentiated morphology, there was a large increase in colony growth and cells were produced in sufficient numbers for the diffusion chamber assay. Thirty one fibroblastic colonies and twenty one adipocytic colonies were isolated either by limiting dilution or ring cloning and then expanded. Of these, eleven fibroblastic and eight adipocytic colonies provided enough cells (2×106 to 2×IO” for implantation and culture in the chambers. Four of the eleven fibroblastic and three of the eight adipocytic colonies formed an osteogenic tissue in the chambers. It was concluded that cells that have differentiated in an adipocytic direction are able to revert to a more proliferative stage and subsequently to differentiate along the osteogenic pathway. Adipocytic and fibroblastic cells cultured in vitro from marrow have, with osteogenic cells, a common precursor in adult marrow.