Ultrastructural characteristics of the incretory granules of the EC- and ECL-cells of the gastrointestinal tract

At least three varieties of EC-cells differing in their density, form and fine structure can be revealed at the ultrastructural study of EC- and ECL-cells of the intestinal tract. Different forms of the incretory granules of the ECL-cells and heterogenous ultrastructural organization of their dense contents in man and animals make is possible not only to distinguish several forms of these cellular elements, but to speak of their specific peculiarities. It is not impossible that the ultrastructural peculiarities revealed in the incretory granules of the endocrine cells explain differences in the nature of histologically active substance which they produce.     

Ultrastructural identification of argyrophil and argentaffin cells of the gastric mucosa in the rat

Ultrastructure of endocrine cells impregnated in the rat gastric mucosa by Grimelius method (identification of argyrophilia) and by Masson--Hamperl method (identification of argentaffinity) and influence of various fixatives on the structure and properties of the secretory granules in these cells have been studied. Fixation of the material in paraformaldehyde or glutaraldehyde varies in its effect on the granule structure of EC-, D1- and ECL-cells, while its influence on the granule structure of G-, D- and AL-cells is identical. The granules of EC-, ECL- and G-cells are argyrophil, and only those of EC-cells are argentaffin. Weak argyrophilia, which is evidently not appearant at the light-optical level, is specific for granules of D1- and AL-cells. Fixation in paraformaldehyde and especially the subsequent treatment in osmium tetroxide results in increasing argyrophilia of the endocrine cells, as compared to fixation in glutaraldehyde. Varieties in the effect of the fixatives do not prevent ultrastructural and histochemical identification of the endocrine cell types.     

Ultrastructure of tissue basophils and capillaries during different periods of pre- and postnatal development of the dermis in the rat

Dynamics of ultrastructure of mast cells (MC) and that of the capillaries of the derma have been studied by means of electron morphometry methods in rats during pre- and postnatal ontogenesis. The dynamics of the Golgi complex volume, that of the mitochondria and specific granules have been calculated in the total volume of the MC membrane organelles. Certain new data have been obtained on the process of the MC specific granules formation in the derma from progranules up to the stage of a mature granule. The process mentioned is most intensive during the first weeks of the postnatal ontogenesis. At the age of two weeks, signs of an active exocytosis of the granules are noted. Judging by certain morphological signs, development of transendothelial transport of substances in capillaries takes place in parallel with formation of the specific granules and corresponds to the beginning of exocytosis of substances in the MC granules. The correlative analysis proves that formation of the MC specific granules is connected with the number of microvesicles in cytoplasm of endotheliocytes.     

Dynamics of the redistribution of pigment granules in the dermal melanophores of anuran amphibians. 1. Dispersion

The dispersion of melanosomes in the dermal melanophores of the Xenopus laevis larvae has been studied by time--lapse cinematography. The process began with the appearance of distally directed melanosome flows in the cell cytoplasm. During the subsequent migration of pigment granules, the flows branched forming branches of the 2nd and higher orders. The whole cytoplasm became filled with a layer of melanosomes. During the dispersion, the movement of melanosomes in a flow is replaced by their dispersion all over the cytoplasm; these processes alternated. In the peripheral part of the cell devoid of melanosomes, membrane vesicles appeared and the cytoplasm was distinctly divided into ecto- and endoplasm. The ectoplasm contained numerous microfilaments and single microtubules, the endoplasm did not contain any cell organelles, except single electron-dense melanosomes. The active role of plasma membrane in the intracellular movement of melanin granules is suggested.     

Vahlkampfia sp: structural observations of cultured trophozoites

Some structural observations on cultured Vahlkampfia sp. trophozoites are reported. Trophozoites are active and pleomorphic, producing large cell protrusions related to locomotion such as lamellipodia, filopodia and endocytic structures formed by hyaline cytoplasm, in which actin provides a framework that allows rapid changes in morphology. As observed by transmission electron microscopy, the cytoplasm is highly granular masking some cell organelles and the major cytoplasmic membrane systems. The structure of cell organelles such as the nucleus, endoplasmic reticulum, and digestive vacuoles is described. A common finding was the presence of 50 nm electron-dense round granules that are not limited by a membrane and that appear scattered in the cytoplasm, and whose function remains unknown. Apparently, the cell reserve material is glycogen, since complete trophozoites were positive to Schiff periodic-acid technique.     

鸟类原生殖细胞的研究 Ⅰ.鸡胚生殖新月区原生殖细胞超微结构的观察

作者观察了鸡胚生殖新月区的原生殖细胞(PGC)的超微结构。PGC为圆形或椭圆形,13—16μm,有丰富的伪足和微绒毛,尚可见到相邻PGC存在桥粒样结构。细胞核为圆形、椭圆形及分叶状,并呈多处凹陷。与同期胚的其它细胞相比,胞质内细胞器相当丰富且较成熟。观察到有大量微丝。上述PGC的形态,除了细胞桥粒样结构及微丝很少见到报道外,其它特征与鸟类PGC的超微记载相一致。 作者首次观察到PGC中有一种特殊颗粒(即电子致密小体),它自核内产生,进入核周池,并借核膜破裂的方式进入胞质。这种颗粒可能就是生殖颗粒,而由该颗粒在胞质中聚集所构成的特殊高电子致密区可能就是生殖质。从而从形态学上提供了鸟类具有生殖质的证据。     

Characteristics of mast cells in Chediak-Higashi mice: light and electron microscopic studies of connective tissue and mucosal mast cells

The beige mouse, a homologue of the Chediak-Higashi syndrome in man, possesses abnormally large granules in many tissue cells. The granules in the mucosal mast cells (MMC) of the small intestine of beige and littermate C57BL/6J mice were examined after infecting the mice with the intestinal parasite, Nippostrongylus brasiliensis. MMC in both beige and littermate mice had irregular granules which contained paracrystalline substructures embedded in an amorphous matrix. Granules were not observed in fusion with the cell membrane. Instead, in late-stage mast cells, the granule membrane broke down, the granule contents were spread throughout the cytoplasm, and the cell organelles disintegrated. Unlike connective tissue mast cells, MMC were poorly demonstrated with formalin fixation and toluidine blue staining.     

Ultrastructure of endocrine cells in the gastric fundal glands at different seasons of the year]

Endocrine cells of gastric glands of Citellus erythrogenus Brandt were studied during various seasons of the year by electron microscopy. ECL, EC, D and D1 cells having different structure of granules were detected. The slightly changed, weakly functioning cells as well as the cells of different alteration degree (up to destructing) were found in hibernating rodents. The presence of actively functioning EC-cells over this period confirms an opinion concerning the influence of peripheral serotonin on the hibernation mechanism. On the 3d--4th day of awakening pronounced activation of endocrine cells, their rejuvenation and normalization of cell ultrastructure, completed two weeks after awakening, were noted.     

Mechanisms of pH regulation in the regulated secretory pathway

A precise pH gradient between organelles of the regulated secretory pathway is required for sorting and processing of prohormones. We studied pH regulation in live endocrine cells by targeting biotin-based pH indicators to cellular organelles expressing avidin-chimera proteins. In AtT-20 cells, we found that steady-state pH decreased from the endoplasmic reticulum (ER) (pH(ER) = 7.4 +/- 0.2, mean +/- S.D.) to Golgi (pH(G) = 6.2 +/- 0.4) to mature secretory granules (MSGs) (pH(MSG) = 5.5 +/- 0.4). Golgi and MSGs required active H(+) v-ATPases for acidification. ER, Golgi, and MSG steady-state pH values were also dependent upon the different H(+) leak rates across each membrane. However, neither steady-state pH(MSG) nor rates of passive H(+) leak were affected by Cl(-)-free solutions or valinomycin, indicating that MSG membrane potential was small and not a determinant of pH(MSG). Therefore, our data do not support earlier suggestions that organelle acidification is primarily regulated by Cl(-) conductances. Measurements of H(+) leak rates, buffer capacities, and estimates of surface areas and volumes of these organelles were applied to a mathematical model to determine the H(+) permeability (P(H+)) of each organelle membrane. We found that P(H+) decreased progressively from ER to Golgi to MSGs, and proper acidification of Golgi and MSGs required gradual decreases in P(H+) and successive increases in the active H(+) pump density.     

Dynamics and 3D organization of secretory organelles of Toxoplasma gondii

Micronemes, rhoptries and dense granules are secretory organelles of Toxoplasma gondii crucial for host cell invasion and formation of the parasitophorous vacuole (PV). We examined whether their relative volumes change during the intracellular cycle. Stereological analysis of random ultrathin sections taken at 5min of interaction, 7 and 24h post-infection demonstrated that the relative volume of each type of organelle decreases just after the respective peak of secretion. Micronemes are radially arranged below the polar ring, while rhoptries converge to but only a few reach the inside of the conoid. In contrast to the apical and polarized organelles, dense granules were found scattered throughout the cytoplasm, with no preferential location in the parasite cell body. Extensive observation of random sections indicated that each organelle probably secretes in a different region. Micronemes secrete just below the posterior ring and probably require that the conoid is extruded. The rhoptries passing through the conoid secrete at a porosome-like point at the most apical region. Dense granules secrete laterally, probably at fenestrations in the inner membrane complex. Immunocytochemistry showed that there are no subpopulations of rhoptries or dense granules, as a single organelle can contain more than one kind of its specific proteins. The vacuolar-like profiles observed at the apical portion of parasites just after invasion were confirmed to be empty rhoptries, as they were positively labeled for rhoptry proteins. These findings contribute for a better understanding of the essential behavior of secretory organelles.     

THE EFFECT OF STRYCHNINE AND LIGHT ON PIGMENTATION IN BLEPHARISMA UNDULANS STEIN

The effect of strychnine sulfate and light on pigmentation in the ciliate protozoan Blepharisma undulans has been determined. Upon exposure of cells to strychnine, the pigment granules become loosened from their surrounding membranes. Eventually these membranes break and the granules are simultaneously released from the cell. At the cell surface, a fusion occurs between adjacent membraneless granules with the incorporation of membrane fragments. This fusion of granules and membrane fragments results in the formation of a pigmented "capsule" around the organism. After elimination of the pigment, the granule membranes remaining in the cytoplasm fuse to form apparently empty vesicles. Other cell organelles are generally undisturbed. A similar situation occurs upon exposure of cells to artificial light for 12 to 18 hr, however, the slow elimination of granules from the cells under these conditions does not result in the formation of a pigmented "capsule." The possible mechanisms of these reactions are discussed.     

Age and changes in the number of endocrine cells in the stomach and their role in senile atrophy of the gastric glands

In the gastric mucous membrane of 40 rats representing 4 age groups (pubertal, mature, old and very old age) per 10 animals in each, thickness of the mucous membrane has been measured by the argyrophil method of Grimelius and the argentaffin method of Masson - Hamperl and the number of the endocrine cells has been counted. The thickness of the mucous membrane and the length of its glands, as well as the number of argyrophil cells increase from the pubertal towards the mature age. From the mature up to the old age the number of argyrophil cells rises in the antral part, and in the acid-producing zone it significantly decreases. The number of argentaffin cells in the stomach does not change from the pubertal towards the old age. In the very old age, against the background of atrophy of gastric glands, the number of both argyrophil and argentaffin cells decreases in both parts of the stomach studied. The data obtained are discussed taking into consideration functional role of various types of endocrine cells, producing biologically active peptides and monoamines.     

The Ultrastructure of Polytomella agilis*

SYNOPSIS Motile cells and cysts of Polytomella agilis, obtained over the entire growth cycle, were examined by electron microscopy. In typical late log phase cells there is a concentric arrangement of the internal organelles around the centrally located nucleus. Lying just beneath the plasma membrane is a peripheral band of elongate mitochondria. Numerous well defined Golgi bodies are also distributed around the nucleus. Vesicles associated with the Golgi body increase in size with distance from the secretory edges of the organelle. Cytoplasmic membranes with associated ribosomes are found between the mitochondrial and Golgi regions. A layer of slender membrane-limited structures is located near the mitochondrial layer. These organelles, which resemble proplastids, become highly branched during late log and early stationary phase, reaching maximum development in late stationary and early pre-cyst stages. Large storage granules of varying density are found within the cell. The PAS-positive granules have been isolated and shown to contain starch. There is an increase in the amount of this storage material as the cells enter the stationary phase. The remainder of the cytoplasmic matrix is finely granular and contains numerous free ribosomes except in the region of the anterior papilla. Four flagella arise from basal bodies at the anterior end of the cell. The cyst is characterized by a thick multi-layered cell wall whose electron density obscures the limiting plasma membrane. Large storage granules are located close to and often in contact with the periphery of the cell, suggesting their involvement in the process of cell wall deposition. Altho mitochondria can still be seen in the mature cyst, other cytoplasmic organelles often appear atypical. The mature cyst has an irregular profile possibly due to shrinkage from dehydration.     

Intracellular Localization of LRV1 in Infected Leishmania Cells and Epitope Conservation of the Coat Protein

ABSTRACT. Polyclonal antibodies were raised against a recombinant fragment of the coat protein of LRV1-1 to determine the epitope conservation of the coat protein among LRV1 isolates, and the intracellular localization of LRV1 particles in promastigote cells of Leishmania braziliensis . Western blot analysis showed that specific epitopes of the coat protein are highly conserved among isolates from different geographic areas. Using indirect immunofluorescence assays LRV1 viral particles were observed as fluorescent granules, limited to the cytoplasm and with no apparent association to the host organelles or the cell membrane, characteristic of a persistent, non-infectious virus.     

Electronmicroscopy studies on the exocrine pancreas of Wistar-Rats following treatment with Streptozotocin.

In Wistar rats the intraveneous injection of streptozotocin (65 mg/kg body weight) caused a permanent hyperglycemia. After 5 days there were lesions in the exocrine parenchyme of the pancreas and its nerve fibers. Pathological changes were found in cytoplasm, cell membrane, nucleus and all other cell organelles, too. The zymogen granules remaining after extensive degranulation may disintegrate in two different ways: 1. Shrinking of the granules and formation of a hale between granule membrane and core, the electronic density of which is decreased; indistinct demonstrability of the granule membrane and finally its decomposition. 2. Shrinking of the granules, decrease of the electron density and either homogeneous or mainly peripheral arrangement of the disintegrated material of the granules; irregular shape of the granules and splitting of their membranes.     

The ultrastructure of prolactin cells in the annual cyprinodont Cynolebias whitei during its life cycle

Summary Prolactin (PRL) cells were studied electron-microscopically and morphometrically in the annual cyprinodont fish, Cynolebias whitei during its life cycle. In prehatching larvae, PRL cells possessed small secretory granules, giant mitochondria and a well-developed Golgi apparatus. During hatching, no changes were observed in the volume density of the secretory granules, indicating that no increased release of PRL occurs at hatching. A significant change in the composition of PRL cells, i.e., the volume densities per cytoplasm volume of the different organelles, occurred between one day and one week of age. Thereafter, only minor differences were observed between age groups, indicating that no major changes occur in PRL cell activity during the lifespan of C. whitei. However, the volume density per cell volume of the nucleus decreased steadily with age during the lifespan. A comparison of the PRL cells in young and adult fish reared in fresh water (FW) with siblings reared from hatching in diluted sea water (1/3 SW) did not reveal any differences with respect to the volume densities of the organelles, including the secretory granules. However, significant differences were observed with respect to the diameter, electron-dense content and affinity to anti- PRL serum of the secretory granules. These differences indicate that, despite the similar volumetric composition of the PRL cells, their secretory granules contain a substantially higher concentration of PRL in FW-reared fish than in 1/3 SW-reared fish.     

Salivary gland of the tick vector of east coast fever. IV. Cell type selectivity and host cell responses to Theileria parva

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000–50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.     

The electron microscopy of normal human oesophageal epithelium.

Oesophageal biopsies were studied with the electron microscope. Three layers were identified, as in the light microscopy of the oesophageal epithelium: basal, prickle and funtional cell layers. A continuous basement membrane separated the lamina propria from the basal cells. The basal cell membrane carried hemidesmosomes, desmosomes and microvillous processes. Their cytoplasm contained the usual organelles plus free ribosomes and tonofirbrils. Prickle cells contained glycogen rosettes and many tonofilaments, and their cell membrane many microvillous and demosomal processes, in places elaborated into desmosome fields. In both these layers there was a wide intercellular space containing some particulate and membranous debris. The flattened cells of the functional layer had fewer desmosomes and microvilli but abundant glycogen and tonofilaments, and a narrow intercellular space. Membrane coating granules first reaching a maximum in the functional cell layer appeared in the upper prickle cell layer and few persisted into the surface cells. The apical cell membrane of the most superficial cells was thickened and had few small microvillous processes, which were covered with a filamentous "fuzzy" coat. No keratohyaline granules were present. Papillae of lamina propria contained capillaries, some with a fenestrated endothelium.     

A membrane hypothesis of aging

Experimental data show that cell membranes become more rigid during aging. If this involves a decrease of resting potassium permeability, the intracellular potassium concentration will increase. Such an increase is beneficial for the maintenance of cell excitability, however, it represents a drawback for the nuclear functions, since the intracellular ionic strength may reach values even above 400 mEq kg^?1 cell water, where the chromatin becomes more condensed and the activity of DNA-dependent RNA-polymerase as well as other enzymes probably decreases. This “membrane hypothesis” of aging may explain the decreased protein synthetic activity of old cells, especially of postmitotic ones.X-ray microanalysis has revealed that potassium concentrations significantly increase in the nucleus and cytoplasm of brain and liver cells of old rats. The chromatin of old nerve cells is more condensed than that of the young ones, the rates of nucleolar and nucleoplasmic RNA-synthesis are significantly lower in the old brain cells, and also the number of perichromatin granules decreases with age.A decrease of intracellular potassium content, in brain cells of old rats can be brought about by phytohemagglutinin-P and centrophenoxine. This is accompanied by a sort of rejuvenation: the chromatin becomes decondensed, the rates of nucleolar and nucleoplasmic RNA-synthesis increase together with the number of perichromatin granules, the medium life-span and the learning capacity of the animals increase. These experimental results support the “membrane hypothesis” of aging.     

Glycogen accumulation in the parathyroid gland of the rat after fluoride ingestion

Summary The parathyroid glands of young male rats given 150 ppm fluoride in their drinking water for 10 weeks were examined by transmission electron microscopy. As a result of fluoride ingestion, the parathyroid chief cells of the experimental animals accumulated glycogen in excess of that seen in control animals given distilled drinking water for the same time period. In the majority of active chief cells, glycogen granules were diffusely spread throughout the cytoplasm as single granules or in small deposits. Large aggregations of glycogen granules were also seen within intercellular spaces. Accompanying the increase in glycogen was a rise in the number and development of the organelles associated with protein synthesis and secretion. The accumulation of glycogen is similar to that in hyperparathyroidism caused by chronic stimulation and prolonged secretory activity of the parathyroid gland. The results of this study suggest that increased amounts of glycogen occur in hyperactive chief cells of the parathyroid in response to the ingestion of large doses of fluoride.