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At least 145 records · Page 8Linked to original sources
PubMed1988

Measurement of the rates of basal pinocytosis of horseradish peroxidase and internalization of heat-aggregated IgG by macrophages from normal and streptozotocin-induced diabetic rats.

The rates of basal pinocytosis and internalization of Fc receptor-bound model immune complexes by macrophages from control (Group 1, n = 9), insulin-treated non-diabetic (2, n = 9), insulin-deficient diabetic (3, n = 8) and insulin-treated diabetic (4, n = 8) rats were measured. Pinocytic rates, as determined by uptake of horseradish peroxidase (HRP), were comparable for all experimental groups (1, 19.6 +/- 5.3; 2, 18.6 +/- 6.0; 3, 18.7 +/- 5.5; 4, 24.5 +/- 9.1; mean +/- 1 SD, pg per min per 10(6) cells, analysis of variance P greater than 0.05). The rates of internalization of Fc receptor-bound model immune complexes were decreased in insulin-treated non-diabetic rats (2, 41.7 +/- 10) and both groups of diabetic rats (3, 39 +/- 5.6; 4, 44.6 +/- 6.9) compared with control animals (1, 54.4 +/- 7.2; mean +/- 1 SD, percentage internalized per 10 min per 10(6) cells, analysis of variance P less than 0.01). Under the conditions of study, comparable amounts of model immune complexes were bound by macrophages from each of the groups; thus, the amount of internalized material was decreased in all three experimental groups (2, 3 and 4). These data suggest that insulin treatment, as well as the diabetic environment, can contribute to a decreased rate of internalization of Fc receptor-bound immune complexes, and may thereby contribute to impaired phagocytosis that has been demonstrated to occur in diabetes. These changes appear to be specific to Fc receptor-mediated internalization, as no differences in the rates of basal pinocytosis were observed.

Animals↗
PubMed1988

Cysticercus bovis: pinocytosis in the Cysticercus tegument.

The authors have found that pinocytosis occurs in the tegument of C. bovis from the fourth week after infection. Electron-lucid bladders surrounded by plasma membrane were encountered in the distal cytoplasm. The pinocytosis occurred in form of micropinocytotic bladders only in the bladder tegument but not in the scolex. The bladders appeared first in the superficial part of the distal cytoplasm. During the following periods of development of the larva they were dispersed in the whole distal cytoplasm and were found even in the processes of subtegumental cells and inside these cells near the heterolysosomes.

Animals↗
PubMed1988

Study on pinocytosis and antigen presentation by murine peritoneal macrophages to T cells in vitro after cisplatin treatment.

Macrophage monolayers showed significantly increased rate of pinocytosis on incubation with cisplatin (10 micrograms/ml). Further, the rate of pinocytosis was compared with macrophages treated with LPS (10 micrograms/ml). Cisplatin treated macrophages also showed enhanced capacity of antigen presentation to T cells in vitro. The antigen presenting capacity of cisplatin treated macrophages was compared with the antigen presenting capacity to LPS treated macrophages.

Animals↗
PubMed1988

Comparative study of assays for stimulated fluid pinocytosis in canine and human neutrophils.

We compared a flow cytometric assay of fluid pinocytosis in stimulated neutrophils with previously used methods, including spectrophotofluorometric assay of fluoresceinated dextran (FD) uptake and beta scintillation spectroscopic assay of radiolabeled sucrose uptake. Neutrophils from human and canine blood were stimulated with formyl-methionyl-leucyl-phenylalanine and phorbol myristate acetate, respectively. Flow cytometry was used to quantitate uptake of FD and lucifer yellow, spectrophotometry was used to quantitate uptake of FD, and spectroscopy was used to quantitate uptake of 14C-labeled sucrose. The flow cytometric assay, using either FD or lucifer yellow, was found to be superior on the basis of maximal incremental increase observed, minimal variability within replicate experiments, and maximal sensitivity to detect early stimulation of fluid pinocytosis in neutrophils.

Animals↗
PubMedDate not supplied

Quantitative evaluation of pinocytosis of capillaries of the stria vascularis under normal and experimental conditions.

In order to examine evidence of high activity of pinocytosis in capillaries of the stria vascularis, quantitative morphometry of pinocytotic vesicles was carried out ultrastructurally by the horseradish peroxidase (HRP) tracer method. In guinea pigs, there was a significant difference between the stria vascularis and spiral ligament in the number of vesicles per micron 2 (p less than 0.05) and labelled vesicles per micron 2 (p less than 0.001). In normotensive control rats, the number of labelled vesicles per micron 2 in capillaries of the stria vascularis was significantly greater (p less than 0.001) than that of the spiral ligament. Results of acute hypertensive and acute hypotensive experiments both indicated that enhanced permeable capillaries of the stria vascularis showed no significant increase in the number of pinocytotic vesicles per micron 2, but that they showed a more significant increase in the number of labelled vesicles per micron 2 than non-enhanced permeable capillaries of the stria vascularis (p less than 0.01) and capillaries of the spiral ligament (p less than 0.001). These findings provide ultrastructural confirmation of our previous studies (4, 8, 9) that pinocytosis contributes to the high permeability of capillaries of the stria vascularis under normal and experimental acute hypertensive and acute hypotensive conditions.

Animals↗
PubMedDate not supplied

[Comparative study of pinocytosis and the production of prostaglandin E2 by hepatic and peritoneal resident macrophages in mice].

Pinocytosis and prostaglandin E2 production are two major functions of the mononuclear phagocyte system. The goal of this study was to compare the pinocytosis of horseradish peroxidase and the prostaglandin E2 production between the hepatic and peritoneal resident macrophages in the mouse. Hepatic resident macrophages were isolated by collagenase digestion, differential centrifugation and adherence. Peritoneal resident macrophages were isolated by peritoneal cavity washing followed by adherence. Horseradish peroxidase was endocytosed by hepatic macrophages at a significantly higher rate (118 +/- 12 ng/10(6) cells/60 min) than by peritoneal macrophages (21 +/- 4 ng/10(6) cells/60 min). Prostaglandin E2 production was measured in the culture medium of unstimulated and lymphokine-stimulated hepatic and peritoneal resident macrophages. Prostaglandin E2 concentration in the culture medium of unstimulated peritoneal macrophages was 36.6 +/- 26.8 ng/ml after a 24 h incubation. It was increased by 83 p. 100 in presence of a lymphokine-enriched secondary mixed lymphocyte culture supernatant. In contrast, hepatic macrophages did not produce any significant amount of prostaglandin E2, even if they were incubated in presence of lymphokines. This study shows that hepatic resident macrophages have a higher pinocytic capacity than peritoneal resident macrophages, suggesting that the role of the liver in the clearance of gut-derived antigens is not only due to its portal irrigation but also to the presence of macrophages highly differentiated in their endocytotic properties. The lack of prostaglandin E2 production in hepatic macrophages, in basal conditions as well as after lymphokine-stimulation, suggests that these cells play a minor role in the regulation of the immune response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

[Studies on pinocytosis of proteoglycans and glycosaminoglycans (author's transl)].

Comparative studies were performed on the uptake of 35SO4-labelled proteoglycans and of free 35SO4-glycosaminoglycan chains by cultured skin fibroblasts. Proteoglycans as well as protein-free polysaccharide chains are internalized by adsorptive pinocytosis. The maximum capacity for endocytosis of proteoglycans is about four times higher than for glycosaminoglycan chains when referred to disaccharide units. On a molar basis about 10 times more glycosaminoglycan chains than proteoglycans can be internalized within a given time. Since unlabelled carbohydrate chains do not compete for the uptake of labelled proteoglycans it seems likely that different receptors exist on the cell surface for endocytosis of both types of macromolecules. 14C-labelled hyaluronate was neither pinocytosed to a measurable extent by skin fibroblasts nor by intima cells cultured from the thoracic aorta. Rat liver hepatocytes efficiently internalized hyaluronate by adsorptive pinocytosis. It was concluded from competitive experiments with hyaluronate oligosaccharides that hyaluronate has to interact with at least two receptor molecules on the cell membrane to achieve endocytosis.

Fibroblasts↗
PubMed1996

Mononuclear cell line THP-1 internalizes bactericidal/permeability-increasing protein by a non-receptor-mediated mechanism consistent with pinocytosis.

BACKGROUND: Bactericidal/permeability-increasing protein (BPI) binds lipopolysaccharide and neutralizes its toxic effects in vitro and in endotoxemic animals. Our recent work identified physiologically significant interactions between BPI, lipopolysaccharide, and mononuclear cells. OBJECTIVE: To determine whether the interaction between BPI and mononuclear cells is receptor mediated. DESIGN: Labeled BPI was incubated with THP-1 cells in the presence of up to 100-fold excess of unlabeled BPI. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting were performed to evaluate competitive binding and total uptake of BPI. Crosslinking was performed to determine whether BPI binds to a single protein entity. Acid washing experiments and flow cytometric analysis were performed to determine whether BPI remains on the cellular surface. Finally, flow cytometry analysis was used to determine whether BPI incubation with THP-1 cells affects the surface expression of the lipopolysaccharide-binding protein-lipopolysaccharide receptor CD14. RESULTS: Labeled BPI uptake was not inhibited by the presence of 100-fold excess of unlabeled BPI at 37 degrees C or 4 degrees C in the presence of azide. Uptake was not saturable under either condition with incubation concentrations up to 10 microgram/mL. Cross-linking did not show BPI bound to a single entity. Acid washing and flow cytometry experiments disclosed rapid internalization of BPI. Finally, BPI uptake by THP-1 cells had no effect on the surface expression of CD14. CONCLUSIONS: Bactericidal/permeability-increasing protein is rapidly internalized by mononuclear cells in a nonspecific fashion not saturable at very high doses, which is consistent with pinocytosis. This process may represent a disposal mechanism for lipopolysaccharide in closed-space infections and may be partially responsible for the rapid clearance of BPI from the peripheral circulation.

Anti-Infective Agents↗
PubMed2002

Contraction-mediated pinocytosis of RGD-peptide by dermal fibroblasts: inhibition of matrix attachment blocks contraction and disrupts microfilament organisation.

Force generation in collagen and matrix contraction are basic functions of fibroblasts and important elements of tissue repair. Cell-matrix attachment is critical to this contraction, involving RGD-binding integrins. We have investigated how this process operates, in terms of force generation (in the Culture Force Monitor) and cytoskeletal structure, using a synthetic RGD-decapeptide. The RGD-peptide blocked force generation over the first 6 h, followed by near complete recovery by 20 h. However, dose response was complex indicating multiple processes were operating. Analysis of cytoskeletal structure after treatment with RGD-peptide indicated major disruption with condensed aggregates of actin and microtubular fragmentation. Fluorescent labeling and tracking of the RGD-peptide demonstrated intracellular uptake into discrete cytoplasmic aggregates. Critically, these RGD-peptide pools co-localised with the condensed actin microfilament aggregates. It is concluded that RGD-peptide uptake was by a form of contraction-mediated pinocytosis, resulting from mechanical tension applied to the untethered RGD-peptide-integrin, as contractile microfilament were assembled. These findings emphasize the importance of sound mechanical attachment of ligand-occupied integrins (e.g., to extracellular matrix) for normal cytoskeletal function. Conversely, this aspect of unrestrained cytoskeletal contraction may have important pathogenic and therapeutic applications.

Actin Cytoskeleton↗
PubMed1987

Inhibition of cell surface ruffling and fluid-phase pinocytosis by microinjection of anti-ras antibodies into living cells.

Fibroblasts transformed by ras oncogenes display enhanced cell surface ruffling and fluid-phase pinocytotic activities. Microinjection of antibodies that specifically bind the ras proteins into these cells results in the inhibition of these two surface activities. The possible underlying biochemical basis of the influence of the ras proteins on membrane ruffling and pinocytosis and the potential relationship of these two biological activities to membrane signal transduction are discussed.

Animals↗
PubMed1984

Metabolism of glycosylated human salivary amylase: in vivo plasma clearance by rat hepatic endothelial cells and in vitro receptor mediated pinocytosis by rat macrophages.

Salivary-type amylase normally comprises about 60% of the amylase activity in human serum, but only a small fraction is a glycosylated isoenzyme (amylase A). In contrast, 1/3 of amylase in human saliva is glycosylated. Since glycosylation can affect circulatory clearance, we studied the clearance of amylase A in rats and its uptake by rat alveolar macrophages. Following intravenous injection, 125I-labeled amylase A disappeared rapidly from plasma (t 1/2 = 9 min) and accumulated in the liver. Simultaneous injection of mannose-albumin slowed its clearance to a rate comparable to that of 125I-labeled nonglycosylated salivary amylase (t 1/2 = 45 min). In contrast, galactose-albumin had no effect. Electron microscope autoradiography of the liver following injection of 125I-labeled amylase A revealed a localization of grains over the hepatic endothelial cells. In vitro studies indicated that amylase A is taken up by alveolar macrophages via receptor-mediated pinocytosis. Uptake was linear over time, saturable, and inhibited by mannan and mannose-albumin, but not by galactose-albumin. We conclude that amylase A, which is a naturally occurring human glycoprotein with at most three terminal L-fucose residues per molecule, is recognized in rats by a mannose receptor located on hepatic endothelial cells. We speculate that this receptor, by rapidly clearing circulating amylase A, may be responsible for the low level of amylase A in human serum.

Amylases↗
PubMed1980

Induction of pinocytosis in cerebral vessels by acute hypertension and by hyperosmolar solutions.

A new approach is described to study the mechanism of protein leakage through the endothelial cells in acute hypertension and after intracarotid infusion of hyperosmolar solutions. The luminarl surface of the cerebrovascular endothelial cells was labeled with choleragenoid-peroxidase before the blood-brain barrier (BBB) dysfunction was induced. Numerous pinocytotic vesicles and some transendothelial channels were formed and showed labeling of parts of their membranes. Our results indicate that the mechanism behind the protein leakage induced by hypertension and by hyperosmolar solutions is the same--ie, transendothelial pinocytosis.

Acute Disease↗
PubMed1992

Coumarins: macrophage proteinase production and pinocytosis.

Coumarins, which are thought to stimulate macrophage proteinase activity, have been advocated for the treatment of high protein oedemas, such as obstructive lymphoedema. In experiments with cultured murine macrophages, coumarin and 7-hydroxycoumarin (10(-3) or 10(-4) M) had no significant effect on plasminogen-activator activity, plasminogen-independent fibrinolytic activity or pinocytosis. Although no in vitro effect on macrophage proteinase activity was found, it is possible that coumarins activate other cell types in vivo and thus effectively treat lymphoedema.

Animals↗
PubMed2000

Low temperature blocks fluid-phase pinocytosis and receptor-mediated endocytosis in Trypanosoma cruzi epimastigotes.

Gold-labeled albumin and transferrin were used to follow at the ultrastructural level the early events and the effect of low temperature on protein uptake by Trypanosoma cruzi epimastigotes. In parasites incubated for 5 min at 28 degrees C with protein-gold complexes, extracellular markers were found only at the cytostome and/or the flagellar pocket regions, whereas intracellular gold particles were detected inside small uncoated vesicles located nearby. Within 10 min, labeling was also observed in uncoated vesicles close to the nucleus. Only after 30 min could the tracers be detected in the reservosomes. Weak labeling in the cytostome and flagellar pocket of parasites incubated at 4 degrees C with the albumin-gold solution indicated that albumin uptake occurred by fluid-phase pinocytosis. On the other hand, intense labeling at the cytostome was observed in parasites incubated at 4 degrees C with gold-labeled transferrin, showing that receptor-mediated endocytosis occurs mainly at this site. Both proteins were absent from the cells at 4 degrees C and 12 degrees C. Raising the temperature from 12 degrees C to 28 degrees C led to transferrin labeling in intracellular vesicles dispersed throughout the cytoplasm, but not in reservosomes. Our results suggest that low temperatures affect the transport and pinching of endocytic vesicles as well as the rate of delivery of transferrin to reservosomes.

Animals↗
PubMed1983

Inhibition by trifluoperazine and digitonin of several forms of pinocytosis.

The effect of the calmodulin antagonist trifluoperazine on fluid phase, adsorptive and receptor-mediated pinocytosis in cultured human fibroblasts and mouse peritoneal macrophages was studied. Uptake in each case was reversibly inhibited by about 20% without toxic effects. Low concentrations of the detergent digitonin had a similar effect. Thus the three uptake mechanisms have common features, and we suggest that in both fibroblasts and macrophages they may reflect uptake within vesicles participating in receptor-mediated endocytosis. These effects of trifluoperazine may operate directly on membranes without the participation of calmodulin.

Animals↗
PubMed1991

Evidence for motility and pinocytosis in ramified microglia in tissue culture.

Ramified microglial cells were investigated in primary cultures of dissociated cerebral cortical tissue from rats. The identification of these cells was confirmed through immunohistochemical staining with 7 monoclonal antibodies selective for microglia. While there was significant variation in staining intensity with different antibodies, all stained the identified ramified cells; the antibodies OX-42 and ED1 yielded the most intense immunoreactivity. Based on distinctive morphological features, the microglia could be identified in living cultures where they were monitored using time-lapse video recording. This technique revealed extremely dynamic features of cellular plasticity and motility. Ramified microglia exhibited constant and rapid alterations in the size and shape of their cell body with an associated extension and retraction of processes; concomitantly, the cells moved about in a circumscribed area. These features of plasticity and motility were unique to this cell type, and correlated with OX-42 immunostaining. The microglia also possessed a differentially high level of pinocytotic activity; this too was correlated with OX-42 staining. From the nature of their morphological plasticity and motility, high pinocytosis, and cellular distribution, it is hypothesized that the ramified microglia specifically function as a system of fluid cleansing in normal brain tissue.

Animals↗
PubMed1981

Pinocytic uptake of divinyl ether-maleic anhydride (pyran copolymer) and its failure to stimulate pinocytosis.

The effect of DIVEMA (pyran copolymer) and three DIVEMA derivatives on the pinocytic uptake of 125I-labeled PVP and colloidal 198Au by the rat visceral yolk sac and by rat peritoneal macrophages was studied in vitro. Contrary to expectations from some earlier data, there was no enhancement of pinocytosis and in some cases inhibition was seen. [14C]DIVEMA and 125I-labelled DIVEMA were accumulated rapidly by rat peritoneal macrophages, the results indicating that this is by an adsorptive pinocytic mechanism.

Animals↗
PubMed1984

Inhibition of pinocytosis and induction of release of lysosomal contents by lysosomal overload of arterial smooth muscle cells in vitro.

Lysosomal overload was induced experimentally in cultured aortic smooth muscle cells by incubation with chloroquine or sucrose. Lysosomal overload was accompanied by a marked reduction in pinocytosis and induced the release of lysosomal contents into the medium. Thus, previously accumulated pinocytic tracer and beta-glucuronidase, a lysosomal enzyme, were released into the medium whereas lactate dehydrogenase, a cytosolic enzyme, was not.

Animals↗