bluuebunny/crossref_metadata_2025_split huggingface dataset:
Segregation of Ferritin in Glomerular Protein Absorption Droplets
Authors: Farquhar Marilyn G. , Palade George E. 
Published: May 2004

Ferritin was used as a tracer to study the mechanism by which proteins are segregated into droplets by the visceral epithelium of glomerular capillaries.
In glomeruli from both normal and aminonucleoside-nephrotic rats ferritin molecules introduced into the general circulation penetrated the endothelial openings and were seen at various levels in the basement membrane. Striking differences between nephrotic and controls were seen only in the amount of ferritin incorporated into the epithelium. In normal animals, a few ferritin molecules were seen in small invaginations of the cell membrane limiting the foot processes, within minute vesicles in the epithelium, or within occasional large vacuoles and dense bodies. In nephrotics, epithelial pinocytosis was marked, and numerous ferritin molecules were seen within membrane invaginations and in small cytoplasmic vesicles at all time points. After longer intervals, the concentration of ferritin increased in vacuoles and particularly within the dense bodies or within structures with a morphology intermediate between that of vacuoles and dense bodies. In nephrotic animals cleft-like cavities or sinuses were frequently encountered along the epithelial cell surface facing the urinary spaces. Some of these sinuses contained material resembling that filling the dense bodies except that it appeared less compact.
The findings suggest that ferritin molecules—and presumably other proteins which penetrate the basement membrane—are picked up by the epithelium in pinocytotic vesicles and transported via the small vesicles to larger vacuoles which are subsequently transformed into dense bodies by progressive condensation. The content of the dense bodies may then undergo partial digestion and be extruded into the urinary spaces where it disperses.
The activity of the glomerular epithelium in the incorporation and segregation of protein is similar in normal and nephrotic animals, except that the rate is considerably higher in nephrosis where the permeability of the glomerular basement membrane is greatly increased.
Formation of Sperm Entry Holes in the Vitelline Membrane of Hydroides hexagonus (Annelida) and Evidence of their Lytic Origin
Authors: Colwin Laura Hunter , Colwin Arthur L. 
Published: May 2004

Electron micrographs of inseminated eggs of Hydroides hexagonus previously had shown that in the immediate vicinity of the penetrating spermatozoön a small portion of the vitelline membrane regularly was absent, and it had been suggested that this area was a hole made by lytic activity of the individual spermatozoön during the course of its passage through the membrane. This deduction would receive support if it could be established that a sperm entry hole does form in living material.
During the present study a hole repeatedly observed and photographed in the membrane of living eggs was found to arise as the spermatozoön penetrated the membrane. Gently compressed eggs formed exovates only through this hole. The holes, and exovates, were not found except at sperm entry sites. It was concluded that this hole is the counterpart of the area from which the membrane is absent in the electron micrographs cited above, and that the spermatozoön makes this hole.
In an electron micrograph two spermatozoa which had penetrated the membrane at separate but closely neighboring points now occupy a single hole. It is argued that if each spermatozoön had displaced the membrane mechanically to make its hole, then there should be two holes, with a partition of membrane between them, but if each had eroded the membrane by applying lysin, a single hole should have formed as the eroded areas expanded and finally merged into one. The latter view agrees with the facts of the electron micrograph. It is concluded that lysis is the most probable means by which the individual spermatozoön makes its hole.
Electron Microscopic Study of the Phagocytosis Process in Lung
Authors: Karrer H. E. 
Published: May 2004

Diluted India ink was instilled into the nasal cavity of mice and the lungs of some animals were fixed with osmium tetroxide at various intervals after one instillation. The lungs of other animals were fixed after 4, 7, 9, 16, or 18 daily instillations.
The India ink was found to be phagocytized almost exclusively by the free alveolar macrophages. A few particles are occasionally seen within thin portions of alveolar epithelium, within the "small" alveolar epithelial cells, or within occasional leukocytes in the lumina of alveoli. The particles are ingested by an invagination process of the plasma membrane resulting in the formation of intracellular vesicles and vacuoles. Ultimately large amounts of India ink accumulate in the cell, occupying substantial portions of the cytoplasm.
The surfaces of phagocytizing macrophages show signs of intense motility. Their cytoplasm contains numerous particles, resembling Palade particles, and a large amount of rough surfaced endoplasmic reticulum. These structures are interpreted as indicative of protein synthesis. At the level of resolution achieved in this study the membranes of this reticulum appear as single dense "lines." On the other hand, the plasma membrane and the limiting membranes of vesicles and of vacuoles often exhibit the double-line structure typical of unit membranes (Robertson, 37).
The inclusion bodies appear to be the product of phagocytosis. It is believed that some of them derive from the vacuoles mentioned above, and that they correspond to similar structures seen in phase contrast cinemicrographs of culture cells. Their matrix represents phagocytized material. Certain structures within this matrix are considered as secondary and some of these structures possess an ordered form probably indicative of the presence of lipid.
The possible origin and the fate of alveolar macrophages are briefly discussed.
Electron Microscope Observations on the Fine Structure of Parietal Cells
Authors: Vial Juan D. , Orrego Héctor 
Published: May 2004

An electron microscope study has been made of the structure of parietal cells in cats, dogs, and rats and of the cells lining the gastric glands of Bufo spinulosus. It is characteristic of all these cells to contain numerous vesicles about 0.05 to 0.3 µ in size. In the mammalian parietal cells an intracellular system of canaliculi is also observed, which is much more complex in the rat than in the cat or dog. Stimulation with histamine causes in the cat a very marked hypertrophy of the canalicular system with development of a large number of villi and a decrease in the number of vesicles. In Bufo, histamine induces the formation of a very complex system of membrane infoldings which circumscribe finger-like processes that entirely fill the glandular lumen. The cytoplasmic vesicles diminish or disappear.
These experiments show that under histamine stimulation all these cells undergo a great increase in the cell membrane area. These findings provide additional circumstantial evidence that parietal cells play a role in the secretion of hydrochloric acid.
The Anatomy of Secretion in the Follicular Cells of the Thyroid Gland
Authors: Wissig Steven L. 
Published: May 2004

The paper contains a description of the fine structure of the thyroid gland of the normal rat.
The follicular colloid, a homogeneous substance of faintly granular texture, is bounded by cuboidal or low columnar epithelial cells. Numerous pleomorphic microvilli, often permeated by small vesicles extend from the apices of the epithelial cells into the colloid. Many small, membrane-limited vesicles lie in the superficial cytoplasmic layer just below the apical plasmalemma. The ergastoplasmic sacs of the follicular cells are dilated and contain a substance resembling colloid. They are of irregular outline, and the larger sacs tend to be located in the base of the cells. The Golgi apparatus lies in the vicinity of the nucleus and consists primarily of numerous small, membrane-bound droplets with a homogeneous content. Droplets, similar to the Golgi vesicles but larger, lie in the same vicinity and are tentatively identified as colloid droplets. The colloid droplets contain an extremely fine, dense particulate material. Other droplets with a denser, more heterogenous content are also present.
Both the follicular cells and the perifollicular capillaries are bounded by a continuous basement membrane. The capillary endothelium is in certain regions extremely attenuated and is pierced by numerous patent pores, 450 A in diameter.
The marked similarity between the presumptive colloid droplets and vesicles of the Golgi apparatus suggests that the droplets arise from this organelle. On morphological grounds alone no relation can be established between any of the organelles of the follicular cell and the process of colloid resorption.
The Lamellar Systems of Cytoplasmic Membranes in Dividing Spermatogenic Cells of Drosophila virilis
Authors: Ito Susumu 
Published: May 2004

Spermatogenic cells of Drosophila virilis were studied by light and electron microscopy. The persistence of a "nuclear wall" during the meiotic divisions has been reported by a number of early cytologists, but this interpretation has been a subject of debate. Electron micrographs of dividing spermatocytes reveal the presence of multiple layers of paired membranes surrounding the nuclear region. These lamellar membrane systems are not typical of the nuclear envelope, but were interpreted as such by light microscopists. The membranes constituting a pair are separated by an interspace of ∼ 100 A and successive pairs are 200 to 400 A apart. These spacings are similar but not identical to those found in the lamellar systems of the Golgi complex. The cisternae of the endoplasmic reticulum in this material are devoid of attached ribonucleoprotein particles, are more precisely ordered than in vertebrate cells, and show a uniform, narrow intracisternal space of ∼ 100 A. The conspicuous asters appear to be made up of similar paired membranes radiating from the centriolar region.
The primary spermatocyte has numerous dictyosomes and a well developed endoplasmic reticulum in cisternal form, but no typical Golgi complex or endoplasmic reticulum is found during the meiotic division stages of metaphase to telophase. Evidence is presented that these cytoplasmic organelles contribute to the formation of the extensive lamellar systems that appear during meiosis. The results of the Golgi silver staining methods and staining tests for phospholipids, basophilia, and the PAS reaction, indicate that the lamellar arrays of membranes present during meiosis are indistinguishable from the Golgi complex in their tinctorial properties.
A Biochemical and Morphological Study of Rat Liver Microsomes
Authors: Moulé Y. , Rouiller C. , Chauveau J. 
Published: May 2004

Microsomes isolated by differential centrifugation from a rat liver homogenate in 0.88 M sucrose solution have been studied from the biochemical and morphological point of view.
1. Under these experimental conditions, the "total microsome" fraction was obtained by centrifuging the cytoplasmic extract free of nuclei and mitochondria, for 3 hours at 145,000 g. Morphologically, the total microsomes consist mainly of "rough-surfaced membranes" and "smooth" ones.
2. The total microsomes have been divided into 2 subfractions so that the 1st microsomal fraction contains the "rough" vesicles (2 hours centrifugation at 40,000 g) while the 2nd microsomal fraction consists essentially of smooth vesicles, free particles, and ferritin (centrifugation of the supernatant at 145,000 g for 3 hours).
3. By the action of 0.4 per cent sodium deoxycholate in 0.88 M sucrose, it was possible to obtain a pellet for each of the 2 fractions which consisted of dense particles, rich in RNA, poor in lipids, and which represented about 50 to 60 percent of the RNA and 10 to 15 per cent of the proteins.
The results have been discussed taking into consideration the hypothesis of the presence of RNA in the membranes of microsomal vesicles.
Electrical Properties of Mitochondrial Membranes
Authors: Pauly Helmut , Packer Lester , Schwan H. P. 
Published: May 2004

The electrical capacity of the membrane of rat liver mitochondria is 0.5 to 0.6 µ./cm2. This membrane capacity is obtained from the analysis of the frequency dependence of the admittance of a suspension of swollen mitochondria.
In potassium chloride media the mitochondrial membrane capacity does not depend on the ion concentration.
The internal conductance of the mitochondria was approximately one-half that of the external medium; the same applies if the mitochondria are equilibrated in a medium with a 10-fold difference in potassium chloride concentration. Hence the swollen mitochondria investigated here appear to be able to adjust their internal ion concentration in proportion with that of the external phase.
The similarity of the membrane capacity of isolated mitochondria with the range of values known for other membranes suggests a common molecular structure.
The analysis of experimental data suggests an anisotropic electrical behavior of the interior of mitochondria. This anisotropy is readily explained by the existence of internal membranes.
Structural Changes in Mammalian Cells Associated with Cooling to -79°C
Authors: Weiss L. , Armstrong J. A. 
Published: May 2004

Suspensions of HeLa and S37 cells, with and without added glycerol, were cooled in stages to -79°C. and held at that temperature for 30 minutes. After warming to room temperature the cells were fixed, sectioned, and compared by phase contrast and electron microscopy with similar specimens kept at room temperature. Correlated viability tests were made.
Abnormal cytological characteristics, visible with the phase contrast microscope, were clearly related to the sequence of freezing and thawing, and the proportion of altered cells was highest in specimens cooled without glycerol. Electron microscopy showed that even in the presence of glycerol all cells were markedly altered, with distinctive vesiculation and disruption of the various intracellular membranes. There is evidence that much cytoplasmic damage is compatible with survival, but it seems likely that separation of the two layers of the nuclear envelope and rearrangement of the nuclear contents are signs of irreversible damage.
The findings lend some support to the belief that cell death on cooling is due largely to denaturation of semipermeable membranes, caused by the increasing concentration of electrolytes.
Concanavalin a and wheat germ agglutinin receptors on dictyostelium: Their visualization by scanning electron microscopy with microspheres
Authors: Molday R , Jaffe R , McMahon D 
Published: May 2004

The cellular slime mold, Dictyostelium discoideum, is a convenient model for studying cellular interactions during development. Evidence that specific cell surface components are involved in cellular interactions during its development has been obtained by Gerisch and co-workers (1, 2) using immunological techniques. Smart and Hynes (3) have shown that a cell surface protein can be iodinated on cells in aggregation phase, but not in vegetative phase, by the lactoperoxidase procedure. Recently, McMahon et al. (4), and Hoffman and McMahon have demonstrated, by SDS gel electrophoresis, considerable differences in cell surface proteins and glycoproteins of plasma membranes isolated from cells at different stages of development.
Plant lectins have also been used to monitor changes in cell surface properties of D. discoideum cells during development. Weeks and co-workers (5, 6) have detected differences in the binding and agglutination of cells by concanavalin A (Con A). Gillette and Filosa (7) have shown that Con A inhibits cell aggregation and prematurely induces cyclic AMP phosphodiesterase. Capping of Con A receptors has also been reported (8). Reitherman et al. (9) have recently reported that agglutination of cells by several plant lectins and the slime mold agglutination, discoidin, changes during development. Such studies indicate that differences in surface properties exist for cells at various stages of development. However, owing to the uncertainties in the factors which contribute to lectin-induced cell agglutination (10), the molecular basis for these observations remain to be determined.
In this study, we have used microspheres (11-14) coupled to either Con A or wheat germ agglutinin (WGA) as visual markers to study by scanning electron microscopy the topographical distribution of lectin receptors on D. discoideum cells fixed at different stages of development. We also describe the effect of labeling on the distribution of lectin receptors and on the morphology of the cell surface.
Nuclear matrix: isolation and characterization of a framework structure from rat liver nuclei
Authors: Berezney R , Coffey DS 
Published: May 2004

A nuclear framework structure termed the nuclear matrix has been isolated and characterized. This matrix forms the major residual structure of isolated nuclei and consists largely of protein with smaller amounts of RNA, DNA, carbohydrate, and phospholipid. The nuclear matrix can be further resolved by combined treatment with DNase and RNase. The remaining nuclear protein structure, after extraction of 90 percent of the nuclear protein, 99.9 percent of the DNA, and 98 percent of the RNA and phospholipid, is termed the nuclear protein matrix. Electron microscopy of this final nuclear protein matrix reveals an interior framework structure composed of residual nucleolar structures associated with a granular and fibrous internal matrix structure. The internal matrix framework is derived from the interchromatinic structures of the nucleus, and is connected to a surrounding residual nuclear envelope layer containing residual nuclear pore complex structures.
Sodium dodecyl sulfate-acrylamide gel electrophoresis of the nuclear matrix proteins demonstrates three major polypeptide fractions, P-1, P-2, and P-3, with average molecular weights of approximately 69,000, 66,000 and 62,000, as well as several minor polypeptides which migrate at approximately 50,000 and at higher molecular weights (&gt;100,000). Polypeptides with molecular weights identical to those of P-1, P-2 and P-3 are also components of isolated nuclear envelopes and nucleoli, whereas isolated chromatin contains no detectable matrix polypeptides. This suggests that the major matrix polypeptides are localized in specific structural regions of the nucleus, i.e., nuclear envelope, nucleoli, and interchromatinic structures. The presence of cytochrome oxidase activity in the isolated nuclear matrix indicates that at least some integral proteins of the nuclear membrane are associated with the matrix.
Movements and associations of ribosomal subunits in a secretory cell during growth inhibition by starvation
Authors: Lonn U , Edstrom JE 
Published: May 2004

In Chironomus tentans salivary gland cells, the cytoplasm can be dissected into concentric zones situated at increasing distances from the nuclear envelope. After RNA labeling, the newly made ribosomal subunits are found in the cytoplasm mainly in the neighborhood of the nucleus with a gradient of increasing abundance towards the periphery of the cell. The gradient for the small subunit lasts for a few hours and disappears entirely after treatment with puromycin. The large subunit also forms a gradient but one which is only partially abolished by puromycin. The residual gradient which which is resistant to the addition of the drug is probably due to the binding of some large ribosomal units to the membranes of the endoplasmic reticulum (J.-E. Edstrom and u. Lonn. 1976. J. Cell Biol. 70:562-572, and U. Lonn and J.-E. Edstrom. 1976. J. Cell. Biol. 70:573-580).
If growth is inhibited by starvation, only the puromycin-sensitive type gradient is observed for the large subunit, suggesting that the attachment of these newly made subunits to the endoplasmic reticulum membranes will not occur. If, on the other hand, the drug-resistant gradient is allowed to form in feeding animals, it is conserved during a subsequent starvation for longer periods than in control feeding animals. This observation provides a further support for an effect of starvation on the normal turnover of the large subunits associated with the endoplasmic reticulum. These results also indicate a considerable structural stability in the cytoplasm of these cells worth little or no gross redistribution of cytoplasmic structures over a period of at least 6 days.
Rearrangements of integral membrane components during in vitro aging of sheep erythrocyte membranes
Authors: Lutz HU , Lomant AJ , McMillan P , Wehrli E 
Published: May 2004

In vitro aged sheep erythrocytes and sheep erythrocyte ghosts spontaneously release vesicles that consist of long protrusions affixed to flattened headlike structures. The intramembranous particles seen on the protoplasmic face of freeze fracture electron micrographs of vesicle protrusions are arranged in paired particle rows. On the equivalent fracture face of headlike structures, the particle density is low; if particles are present, they are clustered along the rim of the flattened headlike structure and at the junction with the protrusion. The released vesicles are depleted of the intramembranous particles seen on the exoplasmic face of ghost but retain almost exclusively particles of the protoplasmic face. Correspondingly, the exoplasmic face of ghosts that have released vesicles reveals a 28 percent higher density of intramembranous particles than that of fresh ghosts.
Purified vesicles are depleted of spectrin but retain integral membrane proteins, with one of an apparent mol wt of 160,000 accounting for nearly 50 percent of the total protein (Lutz, H.U.,R. Barber, and R.F. McGuire. 1976. J. Biol. Chem. 251:3500-3510). When vesicles are modified with the cleavable cross-linking reagent [(35)S]dithiobis (succinimidyl propionate)at 0 degrees C, the 160,000 mol wt protein is rapidly converted to disulfide-linked dimers and higher oligomers. Exposure of intact ghosts to the reagent in the same way fails to yield equivalent polymers.
A comparison of the morphological and biochemical aspects of ghosts and vesicles suggest that a marked rearrangement of membrane proteins accompanies the supramolecular redistribution of intramembranous particles during spontaneous vesiculation. The results also suggest that the paired particles of the protoplasmic face of vesicle protrusions are arranged in paired helices and contain the 160,000 mol wt protein as dimers.