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PubMed1978

In vivo effect of colchicine on hepatic protein synthesis and on the conversion of proalbumin to serum albumin.

Treatment of rats with 0.5-25 mumol/100 g body weight of colchicine for 1 h or more caused an inhibition of hepatic protein synthesis. This effect was not seen if animals were exposed to colchicine for less than 1 h. The delayed inhibition of protein synthesis affected both secretory and nonsecretory proteins. Treatment with colchicine (15 mumol/100 g) for 1 h or more caused the RNA content of membrane-bound polysomes to fall but did not change the polysomal profile of this fraction. By contrast, the total RNA content in the free polysome cell fraction was increased, and this was due to the presence of more ribosomal monomers and dimers. Electron microscope examination of the livers from rats treated for 3 h with colchicine showed an accumulation of secretory vesicles within the hepatocytes and a general distention of the endoplasmic reticulum. Administration of radioactive L-leucine to the rats led to an incorporation of radioactivity into two forms of intracellular albumin which were precipitable with antiserum to rat serum albumin but which were separable by diethylaminoethyl-cellulose chromatography. One form has arginine at the amino-terminal position and is proalbumin, and the other form, which more closely resembles serum albumin chromatographically, has glutamic acid at its amino terminus. Only proalbumin was found in rough and smooth endoplasmic reticulum fractions and in a Golgi cell fraction wich corresponds morphologically to mostly empty and partially filled secretory vesicles. However, in other Golgi cell fractions which were filled with secretory products, both radioactive proalbumin and serum albumin were found. This indicates that proalbumin is converted to serum albumin in these secretory vesicles just before exocytosis. Colchicine delayed the discharge of radioactive albumin from these filled secretory vesicles and caused an accumulation of both proalbumin and serum albumin within these cell fractions.

Animals↗
PubMed1978

Effects of colchicine on ultrastructure of the lactating mammary cell: membrane involvement and stress on the Golgi apparatus.

The effects of colchicine on ultrastructure of the lactating mammary cell in the rat and goat were studied by electron microscopy. Changes in tissue of the rat were examined over time (1, 2 and 4 h). The goat gland was evaluated by comparing ultrastructure of tissue at the time of maximum milk flow suppression induced by the drug with that of untreated tissue. Colchicine produced notable changes in the tissue of both species: 1) the secretion of lipid droplets and Golgi vesicle contents (exocytosis) was inhibited and the droplets and vesicles became randomly distributed throughout the cell, 2) the Golgi apparatus was significantly reduced in size, 3) casein and lipid continued to be synthesized as evidenced by greater numbers of secretory vesicles and increased sizes of casein micelles and lipid droplets, 4) secretory vesicles showed a propensity to cluster around lipid droplets, 5) isolated microtubules were found occasionally in the control tissue, ordinarily in the vicinity of the Golgi apparatus, but rarely in the colchicine-treated tissue. These observations indicate that colchicine has two effects leading to suppression of exocytosis in the mammary cell: one involves early interference with capacity of secretory vesicle membranes to fuse and a further effect, related to higher concentrations of colchicine, causes intracellular disorganization and loss of polarity. Microtubules were not seen as directly involved in the mechanisms of exocytosis. The secretion of milk fat globules is coupled to exocytosis and thereby is also inhibited by colchicine.

Animals↗
PubMed1979

Interaction of retinoic acid and 3-methylcholanthrene on the fine structure of mouse prostate epithelium in vitro.

The effects of 3-methylcholanthrene (MCA) and retinoic acid (RA) on the fine structure of AKR mouse prostate epithelium in organ culture were correlated with changes in cell proliferation. In intact glands before explantation, the epithelial cytoplasm showed concentric flat or globular cisternae of endoplasmic reticulum in both supranuclear and basal areas, a well-developed Golgi complex, secretory vesicles, and numerous microvilli at the luminal surface. After explantation, the cytoplasmic organelles, particularly the endoplasmic reticulum, regressed and tonofilaments appeared. The regression was largely prevented by RA. MCA induced considerable epithelial hyperplasia and squamous metaplasia. The fine structure of the newly formed cells revealed a complete loss of endoplasmic reticulum, Golgi apparatus, secretory vesicles, and microvilli, with the appearance of bundles of tonofilaments and a striking increase in the number of desmosomes. Administration of RA to explants pretreated with the carcinogen partially reversed the hyperplasia and squamous metaplasia. The tonofilaments disappeared and the number of desmosomes greatly decreased, whereas endoplasmic reticulum, Golgi complex, secretory vesicles, and microvilli were largely reestablished. Planimetric measurements of the alveolar epithelium showed that the squamous transformation and its partial reversal by RA coincide with the rise and decline of epithelial hyperplasia. The data suggest that the restoration of secretory differentiation by RA was responsible for the initial breakdown of the hyperplastic epithelium, whereas the lowering of DNA synthesis by RA prevented further hyperplasia and kept cell replication within normal limits.

Animals↗
PubMed1979

Isolation of Golgi fractions from colchicine-treated rat liver. II. Electrophoretic characterization.

1. Intact Golgi fractions, three from colchicine- or ethanol-treated rat livers and two from a control, were analyzed by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. All the fractions showed very similar electrophoretic profiles with 33 protein bands, some of which, especially albumin, had rather higher density in the secretory vesicle fraction than those in the cisternal fraction. 2. Using albumin as the content marker, the Golgi fractions were subfractionated into membranes and contents by freezing-thawing and sonication followed by centrifugation. Distribution of galactosyltransferase among these membrane preparations showed that this enzyme was more enriched in the Golgi cisternal membranes than in the secretory vesicle membranes. 3. All the membrane preparations from the Golgi complex showed very similar patterns on electrophoresis, which were distinctly different from those of microsomal membranes and of plasma membrane. Furthermore, all the Golgi content subfractions had similar protein components, most of which were also found in serum. The microsomal contents, however, showed a considerably different pattern from those of the Golgi contents. 4. From these results it could be concluded that the secretory vesicles are indeed a member of the Golgi complex despite their different appearance and morphology.

Animals↗
PubMed1979

Embryonic development and secretory differentiation in the pars tuberalis of the mouse hypophysis.

The pars tuberalis (PT) of the mouse, like that of other mammals, consists mainly of glandular cells rich in glycogen and peculiar to this lobe. In the mouse, the glandular cells are characterized by large, dense secretory vesicles (up to 300 nm in diameter), the abundance of which indicates a marked secretory activity. The PT develops from a distinct antero-ventral area of Rathke's pouch. The border between the anlagen of the PT and the pars distalis is formed by Atwell's recessus which represents the access for the vessels afferent to the pars distalis. The pedicle of Rathke's pouch is incorporated into the PT anlage, thus contributing to its formation. The entire PT anlage is characterized by glycogen accumulation from the commencement of its formation and persisting in the adult tuberal lobe. Secretory differentiation of the glandular cells of the PT occurs at day 12 of gestation, preceding that of all other adenohypophysial cell types. The secretory features of these cells (development of ergastoplasm and Golgi apparatus, abundance of dense secretory vesicles) appear at an early stage of the enbryonic life (14 days) comparable to those of mature cells. These results confirm earlier observations in the foetal rat where hypophysial secretion also begins in the PT. The existence of peculiar glandular cells speaks in favour of a specific but still unknown function of the PT during foetal and adult life.

Animals↗
PubMed1979

The fine structural effect of sialectomy on the taste bud cells in the rat.

Taste buds in the rat and other mammals share a secretory activity with their transduction function as taste receptor. The present work shows the effect of bilateral removal of the main salivary glands on taste bud cells' components related to secretion in the vallate papilla of the rat. In the sialectomized rats remarkable changes were evidence in the dark and intermediate types of taste bud cells, which are known to be the secretory components. Such changes involve hypertrophy of either the protein synthetizing machinery, the smooth endoplasmic reticulum or the Golgi complex. Lucent and coated vesicles associated to Golgi cisternae increased in number but the amount of dense-core vesicles (secretory vesicles) at the apical cytoplasm of cells decreased. Images of exocytosis of secretory products were observed. The hypertrophy of Golgi complex components was clearly detected with the OsO4 impregnation method for light and electron microscopy. Alteration in the acid phosphatase activity of taste bud cells was not observed in the sialectomized rats. These findings suggest that sialectomy stimulates the entire secretory cycle of dark and intermediate taste bud cells. The light taste bud cells, which are not engaged in secretion, are hardly affected by the treatment. Although taste buds in mammals are neuro-dependent structures, present evidence indicates that they are also sensitive to non-neural influences.

Animals↗
PubMed1979

Isolation of Golgi fractions from colchicine-treated rat liver. I. Morphological and enzymic characterization.

1. Three Golgi fractions, GF-1, GF-2 and GF-3, were isolated from the livers of rats pretreated with colchicine, which gave better yields of the fractions than ethanol treatment of rats. 2. Electron microscopic observation showed that GF-1 was composed mainly of secretory vesicles, GF-3 consisted predominantly of small tubules and flattened cisternae, and GF-2 was an intermediate fraction composed of secretory vesicles and cisternal elements. 3. Among these three fractions the highest activity of galactosyl transferase, marker enzyme of the Golgi complex, was found in GF-3 and the lowest activity was in GF-1, although a different distribution of the enzymes was observed in fractions obtained from ethanol-treated rat liver. 4. Enzymatic characterization of these fractions showed that no significant contamination with other subcellular components occurred in GF-1 and GF-2.

Acid Phosphatase↗
PubMed1979

Cellular mechanisms of proteinase release from inflammatory cells and the degradation of extracellular proteins.

Neutrophils and macrophages produce, store and release large amounts of various acid and neutral proteinases. The two main proteinases of neutrophils are elastase and cathepsin G. They are localized in the azurophil granules, together with proteinase 3 and the acid cathepsins B and D. In addition neutrophils contain collagenase in the specific granules, acid proteinases in the C-particles and plasminogen activator in organelles with the characteristics of secretory vesicles. The granule-bound proteinases are released during phagocytosis while plasminogen activator is apparently secreted. In macrophages, the acid hydrolases are bound to lysosomes while the neutral proteinases are confined to secretory vesicles. The main mechanism of enzyme release in macrophages is secretion. Lysosomal hydrolases are also released by phagocytosis. Enzyme secretion is a characteristic property of activated or inflammatory macrophages. Macrophages become activated after phagocytosis of certain particles and the metabolic burst appears to be an initial event in the activation process. The action of neutrophils and of purified elastase or plasmin on cartilage was tested. These experiments indicate that neutrophil-mediated degradation of cartilage proteoglycans is largely dependent on elastase.

Animals↗
PubMed1979

Metabolic-morphologic events in the integument of the Pacific hagfish (Eptatretus stoutii).

Light- and electron-microscopic autoradiography were used to obtain a coordinated metabolic-morphologic view of some of the events of cellular differentiation that occur across the epidermis of the Pacific hagfish (Eptatretus stoutii) and which enable this animal to secrete copious amounts of mucus. As judged by epidermal incorporation of [3H]-thymidine in vivo, about 98% of DNA replication is confined to the basal three layers of the total of 6--8 layers of cells. Small mucous cells (SMC), the most numerous of the three major cell types involved in mucigenesis, show in vitro and in vivo radioincorporation profiles of [3H]-L-lysine and [3H]-D-glucosamine which differ markedly from those of [3H]-L-fucose and [3H]-D-galactose. Time-course incorporation profiles (mean silver grains/cell and percentage of cells with at least one cluster of silver grains) of [3H]-L-lysine and [3H]-D-glucosamine not only reflected the metabolic activities of cell renewal and differentiation in basally-located cells but also the high mucigenic activity in cells near the epidermal surface. By contrast, [3H]-L-fucose and [3H]-D-galactose were mainly incorporated by the more mature SMC in juxtanuclear regions near Golgi complexes and newly formed secretory vesicles. The intensity of [3H]-fucose labeling appeared proportional to the intensity of histochemical staining of the apical cytoplasm. The prominent capsule, within SMC in basal and lateral regions, which arises from a tight intermingling of tonofilaments, appears to restrict secretory vesicles to apical regions while the cell progressively differentiates and migrates to the epidermal surface. The other mucigenic cell types, large mucous cells and thread cells, each show distinctive differentiation and radioincorporation patterns.

Animals↗
PubMed1979

Preparation of subcellular fractions from granulation tissue by density gradient centrifugation.

The 7000 g pellet of homogenized mature sponge-induced granulation tissue was fractionated by centrifugation in a stepwise sucrose gradient in order to study the synthesis and secretion of collagen and other components of this tissue on the subcellular level. As indicated by chemical and enzymatic assays, by electron microscopy and by incorporation experiments, the collagen-synthethesizing rough endoplasmic reticulum fraction was isolated free from the secretory vesicles (smooth endoplasmic membranes and Golgi elements) and fibrous extracellular matrix. Collagen differed from other proteins in the distribution among the subcellular fractions. In pulse-chase experiment the translocation of 14C-labelled collagen was demonstrated from the rough endoplasmic reticulum through the secretory vesicles to extracellular fibrillar collagen. This fractionation method will be used to study the modulation of collagen synthesis and secretion in the reparative tissue.

Animals↗
PubMed1978

Ultrastructural and histochemical observations on serous ovarian cystadenomas.

One hundred and twelve serous ovarian cystadenomas (46 benign, 33 tumours of borderline malignancy and 33 malignant tumours) were investigated with histological and mucin histochemical methods. Electron microscopy was applied to 9 benign, 6 borderline and 5 malignant tumours. The epithelium of the benign serous cystadenomas contained ciliated and nonciliated columnar cells, which sometimes were edematous ("pale cells"), and smaller basal cells. The large Golgi apparatus with small secretory vesicles and occasional larger secretory granules was located in the apical cytoplasm. There were numerous pinocytotic vesicles at the basal plasma membrane. The extracellular mucin in the cystic lumen and the mucin on the apical epithelial border consisted of material with vic-glycols (1.2-hydroxyl groups) mixed with sulpho- and carboxymucin. With increasing degree of malignancy the number of ciliated cells diminished and were not found in the malignant epithelium. The number of nucleoli and the amount of carboxymucin with sialic acid residues increased with increasing degree of malignancy. However, there were no single consistent ultrastructural feature which could be considered as a reliable criterion for malignancy of these tumours in the absence of invasive growth. The findings support the view that serous ovarian cystadenomas are of coelomic origin.

Adult↗
PubMed1977

Glycosylation of apoproteins of rat very low density lipoproteins during transit through the hepatic Golgi apparatus.

The glycosylation of apo very low density lipoproteins (apo-VLDL) in vivo was studied by following the incorporation of [14C]glucosamine into several groups of apoproteins of VLDL isolated from hepatic Golgi fractions and from serum of sucrose-fed, colchicine-treated rats. Simultaneous incorporation of [3H]leucine was used to quantitate the apoproteins following separation by polyacrylamide gel electrophoresis. Experimental conditions were selected so that the 14C:3H ratio in the apoproteins permitted estimations of the extent of glycosylation by glucosamine and its metabolites. A rapidly decreasing 14C:3H ratio was noted in serum apo-VLDL for the first 30 min after administration of the isotopically labelled precursors, followed by stabilization of the ratio. These data are consistent with the glycosylation of a preformed pool of apo-VLDL, probably apo-B. Glucosamine was progressively incorporated into apo-VLDL during transition from the forming face of the Golgi apparatus to the secretory vesicles, as indicated by an increasing 14C:3H ratio. On the other hand, the ratio of the rapidly migrating apoproteins of VLDL, corresponding to the apo-C-II and apo-C-III, showed the opposite trend, as did total apo high density lipoprotein (apo-HDL) and the rapidly migrating bands of apo-HDL. Division of the rapidly migrating apoproteins of VLDL into upper bands (probably apo-C-II and apo-C-III-0) and lower bands (probably apo-C-III-3) resulted in a 14C:3H ratio near zero in the upper band apoproteins, consistent with the absence of carbohydrates. The lower band showed a rising 14C:3H ratio during transition through the Golgi apparatus, suggesting increased glycosylation, The decreasing 14C:3H ratio in the rapidly migrating proteins is therefore due to the acquisition of apo-C-II and apo-C-III-0 by VLDL during passage from the forming face to the secretory vesicles of the Golgi apparatus.

Animals↗
PubMed1979

A fine-structural analysis of mouse molar odontoblast maturation.

The first mandibular molars of the Swiss albino mice, 1 through 4 days of age, were fixed in glutaraldehyde or Karnovsky's fixative. The tissues were postfixed in OSO4, dehydrated and embedded in Epon. The prepolarizing, polarizing and secretory odontoblasts were described. The prepolarizing cells, located in the vicinity of the cervical loop, were mesenchymal-like in morphology. The cells of the polarizing stage possessed organelles indicative of protein synthesis. The nucleus was located proximally. Aperiodic fibers were evident in the wide basement membrane. The secretory odontoblasts were long, slender, polarized cells closely adjoining one another. Each odontoblast possessed six morphologically discernible regions: (1) an infranuclear region, limited in size and containing few cellular organelles; (2) a nuclear region, housing the oval nucleus and a few associated lamellae of rough endoplasmic reticulum as well as a limited number of mitochondria; (3) a supranuclear rough endoplasmic reticulum region, possessing an abundance of these organelles as well as some mitochondria and secretory vesicles; (4) a Golgi region, occupying the middle third of the cell, housing the elements of an extensive Golgi apparatus which was surrounded by peripherally located profiles of rough endoplasmic reticulum; additionally, this region contained smooth endoplasmic reticulum, mitochondria, numerous secretory granules and vesicles and occasional intracellular collagen fibers; (5) an apical rough endoplasmic reticulum region, containing a rough endoplasmic reticulum component that was less extensive than its supranuclear counterpart; in addition, this region was the one richest in mitochondria and contained a plethora of secretory vesicles and granules; (6) the odontoblastic process, a region mostly void of organelles, containing various secretory products, some of which appeared to be in the process of being released extracellularly into the surrounding dentin matrix.

Animals↗
PubMed1979

Association of centrioles with clusters of apical vesicles in mitotic thyroid epithelial cells. Are centrioles involved in directing secretion?

The ultrastructure of thyroid epithelial cells in mitosis has been investigated. A spatial association is described between clusters of apical vesicles (believed to contain thyroglobulin destined for secretion into the follicular lumen) and centrioles, in late prophase and late telophase cells. Quantitative techniques demonstrate the statistical significance of this association and suggest that it is not related to proximity of the Golgi apparatus or to the location of the centriole in the cell, which changes considerably during these phases of mitosis. The physical basis for this association remains uncertain, but microtubules emanating from the pericentriolar area may be involved. In interphase cells, centrioles are located very close to the follicular lumen, where the majority of apical vesicles are also found. The association of centrioles with clusters of apical vesicles also in mitotic cells suggests that in interphase cells the apically located centrioles may serve as a focus for apical vesicles, helping to direct these secretory vesicles toward the follicular lumen and to maintain cellular polarization. Previous studies demonstrating that centrioles can act as microtubule organizing centers in interphase cells and studies linking microtubules and secretion also tend to support this hypothesis.

Animals↗
PubMed1977

Evidence against phospholipid asymmetry in intracellular membranes from liver.

We have studied the distribution of phospholipids across the membrane of microsomal vesicles and Golgi-derived secretory vesicles from rat liver by the use of phospholipases. Model studies on single-bilayer phospholipid vesicles showed that phospholipase A2 (phosphatide 2-acyl-hydrolase, EC 3.1.1.4) cleaved at least 80% of the lipids on the outer surface of such vesicles without significant attack on the inner surface. In microsomal vesicles approximately 40% of the outer surface phospholipids were cleaved before the enzyme gained access to the interior of the vesicles. The same conclusion was reached for Golgi vesicles. By following the degradation of the three major phospholipids in intact microsomes and in extracted lipids we found that the same fraction of each of these phospholipids was exposed on the outer surface of the microsomal vesicles. Corresponding experiments with Golgi vesicles showed that distinctly different fractions of phosphatidylcholine and phosphatidylethanolamine were present on the surface of these vesicles. However, the difference was accounted for by enrichment of phosphatidylcholine in intravesicular particles rather than by asymmetry across the vesicle membrane. The results from specific hydrolysis of phosphatidylinositol confirmed an essentially symmetric distribution of this phospholipid across the microsomal and the Golgi vesicle membranes.

Animals↗
PubMed1979

Parathyroid hormone biosynthesis. Correlation of conversion of biosynthetic precursors with intracellular protein migration as determined by electron microscope autoradiography.

The formation of parathyroid hormone (PTH) in the parathyroid gland occurs via two successive proteolytic cleavages from larger biosynthetic precursors. The initial product coded for by PTH mRNA is pre-proparathyroid hormone (PreProPTH), a polypeptide of 115 amino acids. Within 1 min of synthesis, the polypeptide, proparathyroid hormone (ProPTH), is formed as a result of the proteolytic removal of the NH2-terminal 25 amino acids from Pre-ProPTH. After a delay of 15-20 min, the NH2-terminal six-amino acid sequence of ProPTH is removed to give PTH of 84 amino acids. To investigate the subcellular sites in the parathyroid cell where the biosynthetic precursors undergo specific proteolytic cleavages, we examined, by electron microscopy autoradiography, the spatiotemporal migration of autoradiographic grains and, by electrophoresis, the kinetics of the disappearance of labeled Pre-ProPTH and the conversion of labeled ProPTH to PTH in bovine parathyroid gland slices incubated with [3H]leucine for 5 min (pulse incubation) followed by incubations with unlabeled leucine for periods up to 85 min (chase incubations). By 5 min, 85% of the autoradiographic grains were confined to the rough endoplasmic reticulum (RER). Autoradiographic grains increased rapidly in number in the Golgi region after 15 min of incubation; from 15 to 30 min they migrated within secretory vesicles still in the Golgi region and then migrated to mature secretory granules outside the Golgi area. Electrophoretic analyses showed that Pre-ProPTH disappeared rapidly (by 5 min) and that conversion of ProPTH to PTH was first detectable at 15 min and was completed by 30 min. At later times of incubation (30-90 min), autoradiographic grains within the secretion glanules migrated to the periphery of the cell and to the plasma membrane, in correlation with the release of PTH first detected by 30 min. We conclude that proteolytic conversion of Pre-ProPTH to ProPTH takes place in the RER and that subsequent conversion of ProPTH to PTH occurs in the Golgi complex.

Animals↗
PubMedDate not supplied

The intracellular pathway for parathormone biosynthesis and secretion.

The initial translation product of parathormone messenger RNA--preproparathormone--is larger than parathormone. Two amino terminal peptide segments of the peptide chain are removed sequentially to form the 84-amino acid hormone. The first cleavage, the removal of a 25-amino acid extension from preproparathormone, occurs in the rough endoplasmic reticulum, and results in the formation of proparathormone. This peptide moves via an energy-dependent mechanism to the Golgi region of the cell where a specific converting enzyme cleaves a basic hexapeptide segment yielding parathormone itself. A part of the newly formed hormone then is enclosed within prosecretory vesicles, transported to the cellular membrane and secreted. Another portion is stored in mature secretory vesicles and is subject to subsequent secretion. The moment to moment control of parathormone secretion by calcium resides at the plasma membrane, but a tightly coupled response at the level of intracellular hormone degradation is also necessary in order to control intracellular hormone levels in the face of rapid changes in secretory rate. Three major secretory products are released from the parathyroid under the control of extracellular calcium: (1) parathormone, (2) a large protein--"parathyroid secretory protein"--whose function is unknown, and (3) peptide fragments of parathormone. Secretion of hormonal fragments adds to the population of parathormone immunoreactivity in the blood. These fragments appear to be similar if not identical to those formed by peripheral metabolism of parathormone in the liver and kidney.

Calcium↗