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Biomedical subjects

M I Cho

Publications and source records attributed to M I Cho.

At least 73 records · Page 4Linked to original sources
PubMed1984

A freeze-fracture study of ruffle-ended post-secretory ameloblasts.

The post-secretory portion of the rat incisor enamel organ was prepared for routine transmission electron microscopy and freeze-fracture replication in order to define further the structural surface features of the ruffle-ended ameloblasts. Surface views of the distal plasma membrane of the ruffle-ended ameloblasts revealed a well-developed zonula occludens junction with from six to ten rows of tight junctional strands. Gap junctions were also observed just proximal to the tight junctional strands. The membranes of the ruffled border contained a rich supply of intramembrane particles (IMP). The IMPs were approximately 7 to 8 nm in diameter and preferentially located on the P-face profiles of the membrane. The density of IMPs on the membranes of the ruffled border was higher than that on the lateral borders of the cell. It is suggested that the IMPs of the ruffled border may represent enzymatic proteins in the basal cell membrane of absorptive ameloblasts. In addition, the large, highly-developed zonula occludens appeared structurally capable of sealing the intercellular spaces between the ruffle-ended ameloblasts.

Ameloblasts↗
PubMed1983

Lytic sensitivity of Actinobacillus actinomycetemcomitans Y4 to lysozyme.

The ability of both human and hen egg white lysozymes to lyse Actinobacillus actinomycetemcomitans Y4 was investigated. Lysis was followed optically at 540 nm by measuring the percent reduction in turbidity of freshly harvested log-phase cells suspended in Tris-maleate buffers within a wide range of pH (5.2 to 8.5) and molarity (0.01 to 0.2 M) and containing various amounts of enzyme and EDTA. In several instances, treated microorganisms were subsequently examined in thin sections by electron microscopy. Reductions in turbidity and clearing of suspensions occurred with small amounts of lysozyme (less than 1 microgram) under relatively alkaline conditions and at low ionic strength and in the presence of small amounts of EDTA (greater than 0.01 mM). Under the most alkaline conditions, EDTA alone effected turbidity reductions similar to those observed in the presence of lysozyme, which suggested that EDTA not only increased outer membrane permeability but also caused cell lysis. Ultrastructural analysis did not always correspond to turbidimetric observations. Cell lysis was virtually complete in suspensions containing both lysozyme and EDTA. However, in contrast to turbidimetric findings, a significant percentage of cells (greater than 25%) was lysed in the presence of lysozyme alone. Furthermore, significant damage occurred in the presence of EDTA alone. Spheroplast-like cell ghosts were present which surrounded condensed cytoplasm or relatively clear spaces. These findings further support the concept of the requirement for electron microscopy to assess lytic damage in addition to turbidimetric and biochemical methods. Our results are the first to demonstrate the remarkable sensitivity of A. actinomycetemcomitans Y4 to lysozyme and to show that EDTA not only affects outer membrane permeability but effects cell lysis, possibly through activation of autolytic enzymes at the cytoplasmic membrane. The exquisite sensitivity of A. actinomycetemcomitans Y4 to lysis could be an important mechanism by which lysozyme participates in the regulation of this suspected periodontal pathogen.

Actinobacillus↗
PubMed1983

The distribution of plasma cells in naturally occurring periodontitis lesions in rats. A light and electron microscopic study.

Plasma cells are widely distributed in inflamed periodontal tissues, the adjacent periodontal ligament and nearby alveolar bone spaces, of old rats (20 and 27 months) raised on a conventional diet in a normal laboratory environment. Electron microscopy revealed three morphologic types (or perhaps stages) of these cells based on the arrangement and content of the granular endoplasmic reticulum. Close contact between plasma cells and other cell types, such as lymphocytes, macrophages and fibroblasts, were commonly observed. It is suggested that plasma cell infiltration is a widespread and prominent feature of naturally occurring periodontitis in old rats, resembling the condition known to exist in humans, monkeys and dogs. The occurrence of large numbers of apparently fully differentiated plasma cells in otherwise normal alveolar bone marrow is discussed.

Alveolar Process↗
PubMed1983

Fibroblast cytotoxicity associated with plasma cells and lymphocytes in chronic periodontitis lesions in rats.

INTERDENTAL PERIODONTITIS LESIONS in rats 20 to 27 months of age were found to contain large aggregations of plasma cells and lymphocytes. Fibroblasts in areas of dense immunocyte infiltration appeared damaged. The close juxtaposition of both plasma cells and lymphocytes to the altered fibroblasts suggests that a cytotoxic effect of immunocyte origin might be a significant element in connective tissue alteration in advanced periodontitis lesions in older rats. At the ultrastructural level, the damaged fibroblasts exhibited alteration of the nucleus, loss of cytoplasmic content including microfilaments and microtubules, swelling and degeneration of mitochondria and Golgi vesicles and cisternae. Dilation of the rough endoplasmic reticulum, including the perinuclear cisterna, along with vesiculation of the cytoplasmic membranes, suggests osmotic dysfunction in various cellular organelles.

Animals↗
PubMed1982

Maturation of human gingival keratinocytes cultured with fibroblasts from keratinizing and non-keratinizing epithelia.

When keratinocytes from epidermis, gingiva and buccal mucosa are cultured in vitro they form a stratified squamous epithelium that lacks evidence of orthokeratinization or parakeratinization. We attempted to induce orthokeratinization or parakeratinization in cultured gingival keratinocytes by co-cultivation with fibroblasts from human skin, gingiva and buccal mucosa. Keratinization was defined by the morphological appearance of the cultured cells and by the presence of large molecular weight keratin proteins (63,000 and 67,000 mol. wt). Using these criteria, the chosen fibroblasts failed to induce any alteration in the pattern of keratinization. We conclude that under our present culture conditions, fibroblasts alone cannot induce keratinization in cultured keratinocytes.

Cell Differentiation↗
PubMed1982

Effects of lysozyme and inorganic anions on the morphology of Streptococcus mutans BHT: electron microscopic examination.

The effects of hen egg white lysozyme and the inorganic salt sodium thiocyanate on the integrity of Streptococcus mutans BHT were studied by transmission electron microscopy. Both control cells and cells exposed to NaSCN possessed thick outer cell walls and densely staining inner cell walls juxtaposed to the plasma membranes. In the presence of NaSCN, however, the S. mutans BHT nucleoid was coagulated into thick electron-dense filaments. Exposure of S. mutans BHT to 150 mug of hen egg white lysozyme per ml resulted in the progressive destruction of both the cell walls and the plasma membranes. The enzyme appeared to affect the region of the cell wall septum, and exposure to 150 mug of hen egg white lysozyme per ml for as short a time as 10 min resulted in visible morphological cell wall alterations. At 30 min, ultrastructural observations revealed that the majority of the cells were in the process of expelling a portion of their cytoplasmic contents from the septal and other regions of the cells at the time of fixation. After 3 h of incubation in the presence of this high lysozyme concentration, gelled protoplasmic masses, which were free from the cells, were evident. In addition, extensive damage to the outer and inner cell walls and to the plasma membranes was apparent, although the cells maintained their shape. On some areas of the cell surface, the outer cell wall and plasma membrane were completely absent, whereas at other locations the outer cell wall was either split away from the inner cell wall and plasma membrane or distended from an area free of inner cell wall and plasma membrane. Upon addition of NaSCN to the hen egg white lysozyme-treated cells, both the gelled protoplasmic masses and the damaged cells exhibited an exploded appearance and existed as membrane ghosts, cell wall fragments, or dense aggregates of cytoplasmic components. The effects of a low lysozyme concentration (22.5 mug/ml) on S. mutans morphology were less pronounced at short incubation times (i.e., 10 and 30 min) than those that were observed with a high enzyme concentration; however, breaks in the cell walls and dissolution of the plasma membranes with resulting cell lysis were visible after a prolonged (3-h) incubation and after subsequent addition of NaSCN.

Cell Membrane↗
PubMed1981

Role of microtubules in the organization of the Golgi complex and the secretion of collagen secretory granules by periodontal ligament fibroblasts.

Fibroblasts of the periodontal ligament (PDL) of the mouse exhibit a high degree of cytoplasmic and functional polarity. This polarity is dependent upon an elaborate system of microtubules. The location of the microtubular arrays and the observed effects of colchicine administration suggest that microtubules play an important role in maintaining the organization of the Golgi complex and its functional relationship to the rough endoplasmic reticulum. Smooth-walled intermediate vesicles, apparently derived from the rough endoplasmic reticulum, are aligned along microtubules at the immature face of the Golgi apparatus, and mature secretory granules are closely related to microtubules at the mature face of the Golgi apparatus. In distal cell processes the granules are closely parallel to microtubules and on occasion bridge-like attachments from granules to microtubules were noted. This relationship of secretory granules to microtubules, the lack of granule storage, and the effects of colchicine on granule secretion suggests that microtubules are part of a mechanism for collagen granule translocation from the Golgi complex to the cell periphery.

Animals↗
PubMed1981

An electron microscopic radioautographic study of collagen secretion in periodontal ligament fibroblasts of the mouse: I. Normal fibroblasts.

Analysis of electron microscopic radioautographs revealed a maximum labeling with 3H-proline of rough endoplasmic reticulum (RER) at 3 minutes, Golgi saccules 1 and 2 at 10 minutes, Golgi saccules type 3 at 20 minutes, and presecretory and secretory granules at 30 minutes. Labeling of the extra-cellular collagen matrix occurred at 30 minutes and increased with time. These observations suggest that pro-a-chains of collagen in periodontal ligament fibroblasts are synthesized in the RER and transported to the Golgi apparatus within 10 minutes. These chains then undergo parallel alignment in Golgi saccules type 2 and form segment-long-spacing-like crystallites in Golgi saccules type 3 between 10 and 20 minutes. The peak labeling of presecretory granules and mature secretory granules in small amounts at 30 minutes and the rapid increase in labeling of extracellular collagen matrix which begins at 30 minutes, indicates that the formation of secretory granules requires approximately 30 minutes and that a rapid system of secretory granule translocation exists in periodontal ligament fibroblasts. This evidence further supports the previously published morphologic evidence for a microtubule-dependent system of collagen secretion in periodontal ligament fibroblasts (Cho and Garant, 1981b).

Animals↗
PubMed1981

An electron microscopic radioautographic study of collagen secretion in periodontal ligament fibroblasts of the mouse: II. Colchicine-treated fibroblasts.

Colchicine administered intravenously depolymerized microtubules and disrupted the normal organization of the Golgi apparatus in periodontal ligament fibroblasts. Radioautography with 3H-proline indicated that collagen secretion was completely inhibited during a period of approximately 4 hours following the onset of the colchicine effect. During this period of secretory inhibition, labeled collagen precursors were present within a variety of dense bodies, primarily located in a juxtanuclear location replacing the normal Golgi complex. The time course of 3H-proline labeling from 2 to 8 hours suggested that small, newly formed dense bodies fused to form larger dense bodies and pleomorphic structures (zebra bodies), within which collagen precursors appeared to undergo partial polymerization. Autophagosomes, many labeled with 3H-proline, also increased in number after colchicine administration. A gradual decline in 3H-proline label occurred from 4 to 24 hours, presumably due to exocytosis of dense bodies or by the digestion of labeled collagen precursors within autophagosomes. These results support the concept that an intact microtubular network is essential for the organized transport of collagen precursors, from the rough endoplasmic reticulum to the Golgi apparatus, and the eventual transport and exocytosis of collagen secretory granules.

Animals↗
PubMed1981

Bacteriolysis of Veillonella alcalescens by lysozyme and inorganic anions present in saliva.

Veillonella alcalescens subsp. dispar was grown in a synthetic medium containing either radiolabeled thymidine or uridine to monitor cell lysis by assay of the release of deoxyribonucleic acid or ribonucleic acid (RNA), respectively. Biochemical analyses demonstrated that, although human or hen egg white lysozymes alone did not release deoxyribonucleic acid or RNA, the nucleic acids were liberated in equal amounts from lysozyme-treated cells by the addition of low concentrations of the sodium salts of HCO-3, SCN-, Cl-, and F-, RNA release was dependent on enzyme and anion concentration. Human lysozyme was more potent than hen egg white lysozyme, and bicarbonate was the most effective anion in promoting bacteriolysis. Surprisingly, ultrastructural analyses differed from biochemical results. Lysozyme alone caused lysis in approximately 40% of the cell population. Detailed ultrastructural examination revealed aggregated cytoplasmic components which appeared as small clumps, explaining why nucleic acids were not measurable in the biochemical assays. In reaction mixtures containing lysozyme plus inorganic salts, electron microscopy results were compatible with biochemical data. Ultrastructural studies demonstrated that the addition of inorganic salts to lysozyme-treated cells resulted in the solubilization of the protoplasmic aggregates of lysed cells, presumably freeing the complexed RNA, and in the rapid lysis of the remaining cells (approximately 60%). These data suggest that electron microscopy must be used in conjunction with biochemical assays to assess lytic damage of bacterial cells.

Anions↗
PubMed1981

Lysis of Streptococcus mutans by hen egg white lysozyme and inorganic sodium salts.

Streptococcus mutans BHT was grown in a synthetic medium containing radioactive thymidine to monitor deoxyribonucleic acid release. Kinetic experiments demonstrated that although lysozyme alone could not liberate deoxyribonucleic acid, cellular deoxyribonucleic acid was liberated from lysozyme-treated cells by addition of low concentrations of inorganic sodium salts. When the salts were tested for their ability to dislodge cell-bound tritiated lysozyme, the extent of the initial release of enzyme by individual anions correlated with the anion potency for deoxyribonucleic acid liberation (SCN- greater than ClO4- greater than I- greater than Br- greater than NO3- greater than Cl- greater than F-), although the total amount of lysozyme dislodged did not correspond directly with cell lysis. Differences in the effectiveness of anions (SCN-, HCO3-, Cl- and F-) in potentiating cell lysis could be enhanced or minimized by varying the lysozyme, anion, and bacterial cell concentrations. As the anion concentration was increased for each enzyme concentration and cell concentration, the lysis increased, in some cases markedly, until maximum levels of released deoxyribonucleic acid were attained. The maximum levels of lysis of SCN- and HCO3- were similar and were greater than those for Cl- and F-. In addition, the maximum levels were observed to increase for each of the anions as the concentration of lysozyme increased.

Anions↗
PubMed1980

Ultrastructure of Merkel cells in the hard palate of the squirrel monkey (Saimiri sciureus).

The distribution and ultrastructure of Merkel cells in the hard palate was investigated in the squirrel monkey (Saimiri sciureus) after fixation by vascular perfusion. Merkel cells were clustered at the base of the epithelial rete pegs of the hard palate. They were characterized by concentrations of dense-cored granules and closely associated intraepithelial nerve endings. Numerous spiny processes extending from the Merkel cell were intercalated with adjacent keratinocytes, probably serving to detect and amplify movement of adjacent cells. These spiny processes contained a rigid core of parallel microfilaments which were interrelated with cytoplasmic filament bundles located beneath the cell membrane. Transitional cells containing dense-cored granules and well developed tonofibrils appear to be related to both Merkel cells and keratinocytes. The findings of this study suggest that Merkel cells are highly adapted for detection of movement in adjacent keratinocytes, as well as movement of the epithelium with respect to the underlying connective tissue.

Animals↗