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At least 577 records · Page 32Linked to original sources
PubMed1998

Mechanisms of uptake of gallium by human neuroblastoma cells and effects of gallium and aluminum on cell growth, lysosomal protease, and choline acetyl transferase activity.

We have studied the uptake and removal of gallium, used as an analogue of aluminum, and the effects of aluminum itself on cultured human neuroblastoma cells treated with soluble metal complexes. The prohibitively high cost of measurement of the only available radioisotope of aluminum (26Al) precluded its usage, and so we considered that gallium, which is chemically extremely similar, would be the most suitable model. Gallium has been used thus in a number of previous biological studies and has been found to behave like aluminum in many respects. We have previously shown that Al-EDTA treatment results in uptake of aluminum and expression of hyperphosphorylated tau, a key component of Alzheimer's disease paired helical filaments. Here we demonstrate that gallium uptake can occur by two separate methods, both leading to physiologically relevant intracellular metal concentrations. Uptake from medium containing bovine transferrin occurred mainly by pinocytosis, but in the presence of human transferrin (hTf), uptake by transferrin-mediated endocytosis occurred also, despite a very low level of hTf saturation, indicating that Tf-mediated uptake is a very effective method of Ga internalization. The intracellular gallium is relatively stable, though partially removable by (1 mM) EDTA, desferrioxamine, or 1,2-dimethyl-3-hydroxypyrid-4-one. Aluminum and gallium treatment were found to increase the overall activity of lysosomal proteases, enzymes implicated in amyloid precursor protein cleavage. No effects were detected on choline acetyl transferase activity, cell growth, or tritiated thymidine incorporation or on the structure of the cells, as judged by light or electron microscopy.

Aluminum↗
PubMed1991

Adrenergic influences on the control of blood-brain barrier permeability.

The central adrenergic innervation of the cerebral microvessels may play a role in the control of blood-brain barrier permeability. To pursue the study of this hypothesis we investigated the effect of noradrenaline on both the permeability of the blood-brain barrier to sodium fluorescein and on the pinocytotic activity of cerebral endothelial cells in the rat. Noradrenaline, stereotactically injected in the right lateral cerebral ventricle, significantly increased the cerebral extraction ratio of sodium fluorescein in a dose-dependent way. The same effect was induced by phenylephrine. Prostaglandin F2 alpha had no significant effect on the passage of sodium fluorescein through the blood-brain barrier. The effect of noradrenaline (150 micrograms) on the cerebral extraction ratio of sodium fluorescein was totally blocked by phenoxybenzamine (25 mg/kg i.p., 24 h before noradrenaline). Noradrenaline (150 micrograms) significantly increased the pinocytotic activity of cerebral endothelial cells. Phenoxybenzamine (as above) reduced the effect of noradrenaline on pinocytosis. It is concluded that noradrenaline increases the blood-brain barrier's permeability to sodium fluorescein, most probably through an effect on alpha adrenoceptors. The increase induced in the blood-brain barrier's permeability by noradrenaline seems to be due, at least in part, to an increase in the pinocytotic activity of endothelial cells.

Animals↗
PubMed1982

A quantitative and qualitative study of blood monocytes in patients with bronchogenic carcinoma.

Absolute circulating number and functions of blood monocytes (i.e., pinocytosis, phagocytosis, and chemotaxis) were studied in 25 patients with untreated bronchogenic carcinoma and in 28 control subjects. The absolute circulating monocyte count was increased in 20 (80%) of the patients. There was no difference in the pinocytic and phagocytic activity of patient and control monocytes. In contrast, patient monocytes showed depressed chemotactic responsiveness. This defect was more severe in small cell anaplastic carcinoma than in the other histologic types of bronchogenic carcinoma (P = 0.0001), and may explain the difference in macrophage infiltration seen in solid tumours of the lung. There was no correlation between chemotaxis and clinical stage. Depressed chemotaxis may be related to a plasma factor, since patient plasma inhibited the chemotaxis of control monocytes as well as the activity of chemotactic agents. The defective chemotaxis and the presence of plasma inhibitory activity may interfere with the ability of blood monocytes to accumulate as macrophages in tumour sites.

Adult↗
PubMed1981

Ultrastructural study of the endothelial cells in teleost liver sinusoids under normal and experimental conditions.

The ultrastructure of the endothelial cells of liver sinusoids was studied in the teleost, Pimelodus maculatus. These cells have the ability to form pinocytotic vacuoles, starting with the formation of marginal folds. The latter occur in many cells after stimulation by India ink injections and ink particles are ingested by pinocytosis and by micropinocytosis. Desmosomes, structures rarely described between liver sinusoidal endothelial cells, are present in this species.

Animals↗
PubMed1981

Ultrastructural study of Kupffer cells in teleost liver under normal and experimental conditions.

The Kupffer cells in the liver of the teleost fish, Pimelodus maculatus, are attached by desmosomes to the endothelial cells lining the sinusoids. These provide a strong attachment allowing them to resist the passage of blood. Following perfusion with India ink, both endothelial and Kupffer cells ingest India ink particles by pinocytosis and micropinocytosis. It is suggested that both cell types may represent two different functional states of the same cell.

Animals↗
PubMed1983

Phagocytosis of rhabdomeral membrane by crab photoreceptors (Leptograpsus variegatus).

Many crabs possess fused rhabdoms which are partly broken down at dawn and re-synthesised at dusk. The cross-sectional area of the rhabdom is therefore smaller during the day than at night. The only previously described mechanism of membrane removal from the rhabdomere in Crustacea involves the formation of pinocytotic vesicles at the bases of the microvilli. The geometry of the rhabdom is such that uniform pinocytosis across the base of each rhabdomere would result in a stack of orthogonally oriented rectangles. In the process described here, microvilli from the outer edges of the rhabdomeres are engulfed by adjacent retinula cells, reducing the number as well as the length of the microvilli and maintaining the smooth longitudinal profile needed for optimal functioning of the rhabdom.

Animals↗
PubMed1982

Rhabdom size and photoreceptor membrane turnover in a muscoid fly.

The cross-sectional area of rhabdomeres in the compound eye of the blowfly, Lucilia, was found to remain constant under 12 h light/12 h dark cyclic lighting, and 10 days constant light or darkness. It was reduced only slightly during 3 h light after 10 days darkness (by 21%), or on exposure to 2 h darkness + 1.5 h light after 10 days light (by 10%). Morphological evidence indicates that shedding of photoreceptor membrane during turnover is achieved by an extracellular route, and by pinocytosis from the bases of the microvilli. The photoreceptor membrane shed by both mechanisms appears to accumulate in multivesicular bodies. The amount of photoreceptor membrane shedding, as indicated by numbers of multivesicular bodies, is constant throughout the day and night on cyclic lighting, decreases in constant darkness, but returns to its normal level after an exposure to 3 h light subsequent to 10 days darkness.

Animals↗
PubMed1982

Transmission and scanning electron-microscopic observations on tanycytes in the mediobasal hypothalamus and the median eminence of adrenalectomized rats.

Tanycytes in the median eminence (ME) of the rat exhibit morphological features suggesting their possible participation in transport phenomena. After adrenalectomy, which modifies the hypothalamo-hypophyseal axis, they undergo morphological changes characterized by an accumulation of lipid droplets, an increased number of bleb-like protrusions at their apex, as well as an increased pinocytosis of intraventricularly injected horseradish peroxidase (HRP). In addition, after adrenalectomy an increased number of vacuoles appears at the level of the tubero-infundibular sulci. Their intracellular location in the tanycytes is demonstrated by an intraventricular injection of HRP. The significance of these vacuoles is discussed in relation to the hydroelectrolytic modifications associated with the state of adrenalectomy.

Adrenal Glands↗
PubMed1978

Filtration effect of endothelial fenestrations on chylomicron transport in neonatal rat liver sinusoids.

The function of endothelial fenestrations in the control of the passage of chylomicrons from the blood to the liver parenchymal cells was studied ultrastructurally in neonatal rats. Measurement of circulating chylomicrons and endothelial fenestrations as well as chylomicrons in the space of Disse at 2--20 h after the onset of suckling revealed a substantial filtration effect of endothelial fenestrations on chylomicrons larger than 250 nm in diameter. Direct uptake of chylomicrons by parenchymal cells was observed to occur by pinocytosis; Kupffer cells endocytosed only very few chylomicrons, and endothelial cells were inactive in this respect.

Animals↗
PubMed1977

Observations on the marginal ruffles of an established fibroblast-like cell line.

LW13K2 cells, a clone of a spontaneously in vitro transformed derivative of embryonic Lewis rat fibroblastic cells, were studied by phase contrast cine-light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ruffles found at the advancing edge of cells grown on glass substrates in vitro form and recede in a period of less than one min if they do not make an attachment of the substrate. If they fail to make an attachment they may form pinocytotic channels near the leading edge as described by Price (1972) and/or collapse, generally backwards, towards the cell body. The "spines" which appear to reinforce the membranous ruffles are the last structures to disappear, and accumulate in an irregular array behind the ruffling edge; this area is behind that in which pinocytosis occurs. In comparison with the sparse numbers of ribosomes found in the trailing edge, they are present in notable concentrations near the leading, ruffling edge of the cell. No membrane vesicles have been found in or near the ruffling edges at the ruffle-spine concentration zone.

Animals↗
PubMed1977

Ultrastructural differentiations in the developing follicle cortex of Locusta migratoria, with special reference to vitelline membrane formation.

Electron microscopic studies on developing follicles of Locusta migratoria show the vitelline membrane to be composed of two ultrastructurally distinguishable components: The vitelline membrane bodies (VMBs) and, in addition, fine granular material, cementing the VMBs together. VMBs form first in the oocyte-near zone within the oocyte-follicle cell space. Subsequently, the second vitelline membrane substance is secreted between the VMBs through apical protrusions of the follicle cells. The possible origin of the VMBs is discussed. Yolk uptake in Locusta seems to occur predominantly by pinocytosis. During oocyte development the oocyte membrane is enlarged by numerous microvilli and folds. In addition pinocytotic vesicles are pinched off. It is supposed that the latter loose their coat and eventually transform into large proteid yolk spheres.

Animals↗
PubMed1976

The fine structure of the perineural endothelium.

Fine strands of motor nerves were examined with the electron microscope using thin section as well as freeze-etching techniques. The specimens were taken from frog cutaneous pectoris nerve, rat sciatic nerve, mouse and shrew phrenic nerves and from human skin nerves. The perineural sheath (Henle, Ranvier, Key and Retzius) consists of one to several concentric laminae of endothelial cells; it encases nerve fascicles and eventually individual nerve fibers and terminals. The endothelial cells are extremely thin and fitted togeether smoothly by overlap and dove-tailing of their border zones. The cell contacts are formed by continuous zonulae occludentes, often reinforced by maculae adhaerentes, and in depth they comprise 3-15 strands with an average of 5-6 strands per junction. The membranes of endothelial cells are studded with attachment sites and stomata of plasmalemmal vesicles suggesting a high level of pinocytotic activity. This phenomenon is by no means restricted to the external laminae of the endothelial sheath. Each endothelial lamina is vested with basement membranes on both (epineural and endoneural) sides, and the spaces between laminae contain a few collagen fibers and fibroblasts. Occasionally, punctate tight junctions are seen between laminae. Cytological evidence supports the hypothesis that the perineural endothelium provides a relatively tight and highly selective barrier separating the peripheral nerves from surrounding tissue and its extracellular fluid spaces. This effect is achieved on the one hand by the sealing of pericellular spaces and on the other hand by a membrane controlled transcellular transport mechanism (pinocytosis), both of which are enhanced by their serial arrangement.

Animals↗
PubMed1975

Effects of induced pinocytotic activity and extreme temperatures on the morphology of Golgi bodies in Amoeba proteus.

The morphology of the Golgi apparatus of Amoeba proteus can be influenced by substances inducing pinocytotic activity as well as by extreme temperatures. During the ingestion of a solution of 0.5% egg white the number of Golgi bodies decreases from 100% measured in control cells to 82% measured in cells showing induced pinocytosis. Simultaneously the ratio of the surface area of the cisternae at the proximal face to that of the vesicles at the distal face of single dictyosomes remains constant (1.74-1.72). The decrease and increase of the temperature of the culture medium to 4 degrees C and 30 degrees C respectively, causes the disappearance of most of the dictyosomes. After keeping the cells for 3-10 h at these temperatures the number of Golgi bodies was only 5-10% of the controls. A continued treatment with cold or warm culture medium leads to a partial reorganization of dictyosomes. After 15 h the number of Golgi bodies counted per cell returned to 57% at 4 degrees C and 38% at 30 degrees C. The ratio of the surface area of the Golgi cisternae to the surface area of the Golgi vesicles also alters under the influence of extreme temperatures. The values measured after treating the cells for 3h, 4 h 10 h and 15 h at 4 degrees C and 30 degrees C amounted to 0.75, 0.85, 1.14 1.53 and 0.93, 0.38, 0.88, 1.60, respectively, compared to 1.72 of control amoebae. The different values of the ratio of the surface area of cisternae to that of vesicles indicate that there are strong morphological changes of single dictyosomes.

Amoeba↗
PubMed1978

Studies on the midgut of Centropages typicus (copepod, calanoid). I. Structural and Ultrastructural Data.

From a structural study of the midgut of Centropages typicus, three main zones presenting different cellular associations may be defined. The ultrastructural study carried out allows us to distinguish several cell types. The four principal cell categories (E, R, F and B) show a more or less marked resemblance with those identified in the Malacostraceans, especially in the hepatopancreas of Decapods. The three types R, F and B, which are subdivided according to their localization (R and R') or their developing stages (F1, F2; B1 to B5), are recognized by the following characteristics: R-cells with smooth endoplasmic reticulum and high microvilli (zones I and III); F-cells with rough endoplasmic reticulum and short or spherical microvilli (zones I and II); B-cells with a large vacuolar apparatus made up of lysosome-like dense bodies associated with vacuoles originating from pinocytosis (zone II). From the comparisons of morphological, ultrastructural and histochemical results concerning Centropages typicus with author's data, we propose and discuss these functions for the three principal cell types: synthesis and secretion of pre-digestive enzymes (F1 and F2-cells); enzyme synthesis, intracellular digestion and extrusion (B1 to B5-cells); absorption (R and R'-cells).

Animals↗
PubMed1975

An ultrastructural study of normal and injured hypoglossal nuclei after injection of horseradish peroxidase.

The left hypoglossal nuclei of normal rats, and rats which had received left hypoglossal nerve axotomies 7-21 days previously, were studied by electron microscopy after injection of horseradish peroxidase as a marker of extracellular space and pinocytosis. Quantitative analysis showed that the number of pinocytotically-derived structures in presynaptic boutons was significantly increased in rats at 7, 14, and 21 days after axotomy when compared with normal rats. It was suggested that presynaptic boutons which became detached from injured neurones retracted by a membrane cycling mechanism involving pinocytotic uptake of bouton plasmalemma, without compensatory membrane production elsewhere. It was confirmed that the channels in the microglial cells communicated with the extracellular space.

Animals↗
PubMed1979

In vitro induced pinocytotic activity by a juvenile hormone analogue in oocytes of Drosophila melanogaster.

Pinocytotic activity has been analyzed in Drosophila oocytes following either in vivo or in vitro exposure to horseradish peroxidase. The enzyme tracer gains access to the yolk spheres only when supplied to the oocyte in vivo. In oocytes cultured in vitro, peroxidase remains restricted to the residual coated vesicles and to the tubular profiles formed in excess in the cortical ooplasm. In an attempt to induce peroxidase uptake by oocytes cultured in vitro, various incubations were tested. Among these, hemolymph from both sexes is capable of promoting peroxidase uptake up to a level comparable to that detectable in vivo. On the other hand, fat body extracts fail to promote such cellular activity. Finally, the juvenile hormone analogue ZR-515 is shown to be the only factor required to promote pinocytotic activity under the experimental conditions tested. The observations are interpreted to indicate that vitellogenin has no inductive role on pinocytosis but simply acts by adhering to the forming coated vesicles which in turn are produced by the oolemma in response to the action of juvenile hormone.

Animals↗
PubMed1981

The development of the stomach in clarias lazera and the intestinal absorption of protein macromolecules.

The development of the stomach of the teleost, Clarias lazera, during the early posthatching period, is described, and the developing stomach is compared with that of adult Clarias. The stomach develops in two distinct parts: the corpus, which differentiates first, and the pylorus. The corpus contains a mucous surface epithelium, arranged in folds, and a tubular gland system containing only one type of gland cell, to which the secretion of pepsinogen and HCl is attributed. The pyloric region does not contain tubular glands. From the ultrastructure of the gland cells, the 3H-thymidine labeling index, and the onset of acid production (as determined with pH indicators) it is concluded that a functional stomach is present in juveniles with a standard length of +/- 11 mm (approximately 12 days after fertilization at 23-24 degrees C). The ultrastructure of the intestinal epithelium has also been studied. The intestine consists of three segments, similar to those described for stomachless teleosts and a number of fish larvae. In larvae as well as in juveniles, the enterocytes of the second segment show pinocytosis of horseradish peroxidase, although in the juveniles the stomach has already developed. This second segment has the same relative length in all studied larvae and juveniles and is also present in adult Clarias. It is therefore concluded that the capacity to absorb protein macromolecules is not specifically related to the absence of a functional stomach in this teleost species.

Absorption↗
PubMed1986

Heterozygosity for phosphodiester glycosidase deficiency: a novel human mutation of lysosomal enzyme processing.

We have carried out studies on the fibroblasts of III-3, a clinically normal Lebanese individual previously reported to have abnormally high plasma lysosomal enzyme levels. Mannose-6-phosphate (man-6-P) receptors in III-3 fibroblasts were found to be functioning normally, but the cells had only half normal levels of phosphodiester glycosidase activity. Pinocytosis of III-3 fibroblast secreted beta-hexosaminidase B (hex B) into Sandhoff disease fibroblasts was 18% of control, and the apparent KD for binding of III-3 hex B to man-6-P receptors was 3.7 X 10(-9) M compared to 1.25 X 10(-9) M for control enzyme. Hex B secreted by III-3 fibroblasts included an enzyme pool less electro-negative than control enzyme which had a very low affinity for man-6-P receptors and which did not bind to DEAE-Sephadex. Treatment of this abnormal hex B with exogenous placental phosphodiester glycosidase increased its binding to man-6-P receptors three-fold. Secretion rates of seven lysosomal enzymes from III-3 fibroblasts were, on average, twice as great as rates measured for two I-cell disease heterozygote fibroblast lines. The results suggest that III-3 fibroblasts are heterozygous for phosphodiester glycosidase deficiency. The possibility that an individual homozygous for this enzyme deficiency would develop I-cell disease is discussed.

Carrier Proteins↗