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At least 37 records · Page 2Linked to original sources
PubMed1990

Stimulation of growth hormone and prolactin release from rat pituitary cell aggregates by bombesin- and ranatensin-like peptides is potentiated by estradiol, 5 alpha-dihydrotestosterone, and dexamethasone.

The effect of the bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin-C (NMC), and the ranatensin-like peptides, neuromedin-B (NMB), neuromedin-B30 (NMB30), and neuromedin-B32 (NMB32), on pituitary GH and PRL release was studied in perifused anterior pituitary aggregate cell cultures from 9- to 12-week-old male rats cultured in serum-free defined medium supplemented with 0.05 nM T3 and 4 nM dexamethasone (DEX). All peptides stimulated PRL and GH release. GRP and NMC stimulated hormone release in a concentration-dependent manner between 0.1-10 nM. NMB was slightly more potent than NMB30 and NMB32, but was significantly less potent than GRP and NMC. The magnitude of the PRL response to GRP and NMC inversely correlated with that of the GH response. Cultures with relatively low PRL response levels displayed high GH responses, whereas the opposite was found in cultures with high PRL response levels. The stimulatory actions of GRP, NMC, and NMB were blocked by the bombesin receptor antagonist Leu13 psi (CH2NH) Leu14-bombesin, supporting the specificity of the findings. Addition of 1 nM estradiol (E2) to the culture medium provoked an impressive (4- to 10-fold) increase in the magnitude of the GH response to NMC without changing the EC50 value (0.5 nM). In contrast, E2 significantly decreased the stimulation of GH release by rat GH-releasing factor. In the E2-treated aggregates 3 nM NMC stimulated GH release to a comparable extent as 0.1 nM GRF. 5 alpha-Dihydrotesterone (10 and 100 nM) and DEX (80 nM) also enhanced the GH response to NMC, but to a much smaller extent than E2. E2 had also a stimulatory effect on the PRL response to NMC, particularly in cultures with a low intrinsic PRL response. The PRL response to NMC was decreased by DEX and slightly augmented by 5 alpha-dihydrotestosterone. It is concluded that bombesin- and ranatensin-like peptides have a stimulatory effect on GH and PRL release at the pituitary level. Since their action on GH release is strongly potentiated by E2 and much less so by glucocorticoids, these peptides clearly distinguish their activity and specificity from that of the protagonist releasing factor GH-releasing factor, suggesting a role in sex-related differences in GH release or in the control of GH secretion during sexual maturation.

Animals↗
PubMed1990

The effect of amiloride on the cardiac chronotropic responses to isoproterenol in myocardial aggregate cells in culture.

The purpose of this study was to test the hypothesis that amiloride alters the response of cardiac myocytes to isoproterenol. Myocardial cell aggregates were prepared from 7 day-old chick embryos maintained in culture for 72 hrs before study. Isoproterenol, 10-8 M to 10-5 M, significantly (P less than 0.05) increased contractile frequency of myocardial aggregates. The effects of isoproterenol were maximum within 5 min. of exposure and declined thereafter. In the absence of isoproterenol, amiloride, at 10-6 M and 10-7 M produced a transient decrease in contractile frequency while amiloride at 10-5 M produced a significant (P less than 0.05) decrease in contractile frequency. Amiloride significantly (P less than 0.05) increased the effect of isoproterenol on cardiac contractile frequency. There was a greater and more sustained response to isoproterenol in the presence of amiloride. Furthermore, the magnitude of these effects were greater with higher concentrations of amiloride. These data indicate that amiloride accentuates the cardiac chronotropic response to isoproterenol and suggest that, because amiloride inhibits sodium entry in these cells, change in intracellular sodium may be one of the mechanisms mediating the chronotropic action of isoproterenol on the heart.

Amiloride↗
PubMed1988

Signal transduction, chemotaxis, and cell aggregation in Dictyostelium discoideum cells without myosin heavy chain.

Dictyostelium discoideum cells have been generated that lack myosin heavy chain (MHC) due to antisense RNA inactivation of the endogenous mRNA or to insertional mutagenesis of the myosin gene. These cells retain chemotactic movement in gradients of the chemoattractant cAMP. Furthermore, cAMP does induce many biochemical and physiological responses in aggregative cells, including binding of cAMP to surface receptors, modification, and down-regulation of the receptor; activation of adenylate and guanylate cyclase, secretion of cAMP; and the association of actin to the Triton-insoluble cytoskeleton. Cells lacking MHC were found to have a requirement for bivalent cations in the medium for optimal chemotaxis and cell aggregation.

Actins↗
PubMed1988

Fahraeus-effect-reversal (FER) in compaction stasis (CS): microrheological and haemodynamic consequences of intravascular sedimentation of red cell aggregates.

Red cell aggregate sedimentation under gravitation produces pronounced and rapid "phase separation effects" culminating in "compaction stasis" (CS), i.e. almost complete stuffing of microvessels by RBC. This can be readily observed and monitored in microvessels of vertically placed mesentery preparations by a horizontally aimed intravital microscope as shown by (GOBEL et al. VIRCHOW's Arch., 1988,). "Layered flow", floatational plasma skimming and progressive increase in local tube hematocrit (HT) up to 100% ("compaction stasis") occurs during induced low flow states in vivo (here preferentially in postcapillary venules), as well as in vitro (non-permeable artificial micro tube networks). Quantitative densitometry and velocimetry in vertically placed microvessels demonstrates that the process of RCA sedimentation results in progressive vertical skewing of the velocity profile, culminating in standstill of the RBC-sediment in the dependent vessel half, with superfluent plasma and small aggregates in the upper vessel half. The theory of compaction stasis is developed: in striking contrast to the situation under high shear conditions, red cells travel on slower trajectories than plasma: due to "red cell undervelocity" the average residence times of RBC in a venule is much higher than that of plasma. Consequently, CS can be explained as the result of a FAHRAEUS effect reversal since the principle of mass conservation requires that HT much greater than HD. Network aspects and hemodynamic consequences are also incorporated into the theory.

Animals↗
PubMed1990

The ultrastructure of imaginal disc cells in primary cultures and during cell aggregation in continuous cell lines.

We have examined the ultrastructure of cellular vesicles in primary cultures of wing imaginal disc cells of Drosophila melanogaster. These cells maintain the apico-basal polarity characteristic of epithelial cells. The apical surfaces secrete extracellular material into the lumen of the vesicle from plasma membrane plaques at the tip of microvilli. During the course of one passage, cells from the established cell lines grow to confluence and then aggregate into discrete condensations joined by aligned bridges of cells. Cells in these aggregates are tightly packed, and there appears to be a loss of the epithelial polarity characteristic of the vesicle cells. Elongated cell extensions containing numerous microtubules are found in aggregates, and we suggest that these may be epithelial feet involved in the aggregation process. Virus particles are commonly found both within the nucleus and the cytoplasm of cells in the aggregates.

Animals↗
PubMed1982

[Activation and cell-aggregation of mononucleus cells after short-term stimulation with mitogen and tuberculin].

The aim of the study was the description of morphological changes in mononukleated cells after short-term stimulation by mitogen and tuberculin visible by light- and electronmicroscopy and in differences between nucleus areas measured by planimetry. Already 1 hr. after p.h.a. stimulation lymphocytes forme clusters in which the mononucleated cells were present mostly as irritated and exhausted cells. In PPD-stimulated lymphocytes clusters were formed after 16 to 24 hrs. These cells were activated. Within clusters strong intercellular contacts were visible using the electron-microscopy. The results of planimetry in regard to nucleus areas of lymphocytes and monocytes were significantly dependent from the kind of mitogen or antigen and the duration of incubation time (analysis of variance).

Cell Aggregation↗
PubMed1986

Invasion of human embryonic fibroblast cell aggregates by rat tumor cells of different metastatic capacities.

Aggregates of normal human Wi38 cells are used as a three dimensional substrate to test in vitro the behavior of rat tumor cells which exhibit different invasive and metastatic capabilities in vivo. The invasive but non metastatic tumor cells colonize the Wi38 cell aggregates, invade and destroy them within three days. The non invasive but highly metastatic tumor cells settle in a limited number on the aggregates but show no further activities. Co-cultivation of these tumor cells with cell suspension of single Wi38 cells under aggregation conditions does not hinder the Wi38 cells in forming aggregates. The results show that the invasive process in the metastatic cascade needs more specific reaction partners and host environment than local tumor growth. The conditions of the first process cannot be mimicked by a simple model.

Animals↗
PubMed1989

Re-expression of 117 antigen, a cell surface glycoprotein of aggregating cells, during terminal differentiation of Dictyostelium discoideum prespore cells.

117 antigen is a glycoprotein expressed on the surface of D. discoideum cells at aggregation. It then disappears and is later re-expressed on the surface of a subpopulation of cells at culmination, the terminal differentiation stage (Sadeghi et al. 1987). A cDNA clone was used to show that the appearance of cell surface 117 antigen accurately reflects the expression of the 117 gene as measured by mRNA levels. It was also shown that during multicellular development there is a reciprocal relationship between the levels of 117 mRNA and the mRNA which codes for prespore surface glycoprotein, PsA. Dual parameter flow cytometry was used to demonstrate that the 117 antigen is found on the surface of maturing prespore cells after the PsA glycoprotein disappears, but that it is not found on mature spores. Using three monoclonal antibodies which identify respectively 117 antigen, PsA, and MUD3 antigen (a spore coat glycoprotein--probably Sp96), two new stages of final spore maturation were defined. These results indicate that there is a recapitulation of at least one aggregative cell surface glycoprotein in the prespore subpopulation of cells as they rise up the stalk during final spore development. This raises the possibility that culmination, which involves complex three dimensional morphogenetic movements not unlike those observed during animal embryogenesis, involves components of the two-dimensional pattern seen during aggregation.

Antigens, Differentiation↗
PubMed1980

Sponge cell aggregation.

Dissociated sponge cell system has proved to be a useful model to study the process of cell aggregation both on cellular and subcellular level. The purpose of this review is to discuss recent results obtained from experiments with the marine sponge Geodia cydonium. Dissociated cells form functional aggregates during a process which can be sub-divided into three phases: first, formation of small primary aggregates in the presence of Ca2+; second, formation of secondary aggregates in the presence of an aggregation factor and third, reconstitution of a functional system of water-containing channels by rearrangement in the secondary aggregates. On subcellular level a series of macromolecules are known which are involved in the control of aggregation and separation of sponge cells: Aggregation factor, aggregation receptor, anti-aggregation receptor, beta-glucuronidase, beta-glucuronosyltransferase, beta-galactosyltransferase, beta-galactosidase and a lectin. These components might be linked in the following sequence: (a) Activation of the aggregation receptor by its enzymic glucuronylation; (b) Adhesive recognition of the cells, mediated by the aggregation factor and the glucuronylated aggregation receptor; (c) Inactivation of the aggregation receptor by its deglucuronylation with the membrane-associated beta-glucuronidase; (d) Cell separation due to either the loss of the recognition site (glucuronic acid) of the aggregation receptor for the aggregation factor or to an inactivation of the aggregation factor by the anti-aggregation receptor. The activity of the anti-aggregation receptor is most likely controlled by the Geodia lectin. The events leading to cell-cell recognition cause a change in the following metabolic events: Increase of oxygen uptake, decrease of cyclic AMP level, increase of cyclic GMP level and stimulation of programmed syntheses.

Animals↗
PubMed1978

Biochemical and morphological comparison of two tumour-cell-aggregation factors from rat ascites hepatoma cells.

Two tumour-cell-aggregation factors, derived from rat ascites hepatoma cells, had different antigenicity; one was not absorbed by immunoadsorbent chromatography with anti-rat serum antibody and the other was. Their activities were both lost by digestion with trypsin, but remained unchanged by oxidation with periodate, suggesting the role of the protein portions in their molecules. The potency of the unabsorbed factor was inhibited specifically by alpha-methyl-D-mannoside or D-mannose, while that of the absorbed factor was inhibited specifically by N-acetyl-D-glucosamine, suggesting that these carbohydrates may be concerned with the respective receptor structures at the tumour-cell surface. The unabsorbed factor induced not only cell aggregation (as shown in the form of simple apposition) but also cell adhesiveness characterized by development of intermediate junctions, desmosomes and tight junctions, while the absorbed factor produced only simple apposition, suggesting their functional difference.

Animals↗
PubMed1979

Production of plasminogen activator and inhibition of embryonic cell aggregation by cultured human normal and neoplastic cells.

The plasminogen activator (PA) production and the capacity to inhibit embryonic neural retina (NR) cell aggregation by human normal and neoplastic cell lines have been studied. The PA production was detected by both iodinated fibrin and casein lysis assays, and by changes in cell morphology at the presence of activated PA, using dog serum. Since the casein lysis assay and morphological changes proved to be less sensitive than 125I-fibrin lysis assay, a good correlation between these three assays could be observed provided that PA production measured by fibrinolysis exceeded 10--20%. The neoplastic cell lines exhibited the PA production to quite a large extent. The highest fibrinolytic activity (78%) was found in the case of bladder carcinoma cells T24, while the B-5GT cells from giant cell tumor of bone failed to produce any detectable amount of the PA. The cells from synovial sarcoma and both glioma lines exhibited fibrinolytic activity of about 10% and four sarcoma cell lines over the range 20--50%. Out of 13 normal cell lines tested, 7 were negative or exhibited very low fibrinolysis not exceeding 3% of total radioactivity. Four cell lines derived from kidneys, lungs, intestines, and from mixed embryonic tissues showed a marked fibrinolytic activity of about 10--37%, a slightly elevated fibrinolysis being found in embryonic lung cells LEP and cells from fetal skin tissue only at the presence of dog serum. The fibrinolysis detected in the neoplastic cloned cell populations showed considerable differences in the PA production between individual cell clones isolated from the same parental cell line. Unlike the normal fibroblastic cells B-41FB derived from bone, all neoplastic cell lines tested possess the capability to inhibit embryonic NR cell aggregation significantly. The results suggest the effect not to be dependent upon the PA production.

Animals↗
PubMed1978

Embryonic tissues as elasticoviscous liquids. I. Rapid and slow shape changes in centrifuged cell aggregates.

Certain embryonic tissue masses and cell aggregates behave like deformable solids during brief experimental manipulations but like viscous liquids in long-term organ cultures. To investigate these seemingly paradoxical physical properties, we have mechanically deformed cell aggregates derived from several embryonic chick organs by centrifuging them against solid substrata. Aggregate shapes during brief centrifugation were observed directly in a microscope-centrifuge. In addition, techniques were devised for fixing cell aggregates during prolonged centrifugation. Evidence presented here shows that these fixative-injection procedures accurately preserve the prefixation shapes of living centrifuged aggregates. According to a simple viscous-liquid model for cell aggregates, cohering cells slide past one another when external forces and/or tissue surface tensions cause gradual rearrangements in aggregate conformations. In earlier experiments, 2 types of behaviour predicted from this model were confirmed for several embryonic chick tissues subjected to prolonged centrifugation. First, initially flat aggregates rounded up against the centrifugal force to adopt the same shapes that initially round aggregates reached by flattening. Second, the relative roundness of centrifuged aggregates of different tissues at shape equilibrium correlated with the relative positions that these tissues assumed when they were combined in aggregate-spreading and cell-sorting experiments. By contrast, the brief centrifugation experiments described here provide some support for a simple elastic-solid model in which aggregate shape changes are accompanied by cell deformations rather than cell redistributions. In particular, since cell migration tends to occur quite slowly, the very rapid aggregate flattening observed during the first few minutes of centrifugation presumably requires cell stretching. Moreover, since they do also round up very rapidly following brief centrifugation, these aggregates exhibit considerable elasticity that presumably reflects the swift relaxation of cell stretching as the centrifugal force is removed. Athough both elastic-solid and viscous-liquid properties can be recognized in cell aggregates, we note that, in the prolonged centrifugation experiments described here, rapid initial aggregate flattening is followed by much more gradual, continued flattening. Similarly, after prolonged centrifugation, rapid partial aggregate rounding-up is also followed by much more gradual, continued rounding-up during subsequent culture at Ig. Such rapid-then-slow shape changes contradict both simple elastic-solid and simple viscous-liquid models for cell aggregates. These bimodal shape changes are instead consistent with both compound-viscoelastic-solid and elasticoviscous-liquid models for cell aggregates, although only the latter can also account for long-term liquid-like aggregate behaviour...

Animals↗
PubMed1985

[3H]N-Methylscopolamine binding to muscarinic receptors in intact adult rat brain cell aggregates.

Intact brain cell aggregates were dissociated from adult rat brains, by a simple sieving technique, and were used to study the binding characteristics of [3H]N-methylscopolamine to muscarinic acetylcholine receptors. The magnitude of binding of this ligand was related linearly to the amount of cell protein in the binding assay, with a high ratio of total to nonspecific binding. In addition, specific binding showed saturability and high affinity. Muscarinic receptor antagonists displaced specific [3H]N-methylscopolamine binding according to the law of mass-action, while it was possible to resolve displacement curves using receptor agonists into high- and low-affinity components. The results are discussed in terms of the usefulness of dissociated intact rat brain cells in studying muscarinic acetylcholine receptors in the central nervous system.

Animals↗
PubMedDate not supplied

[Induced cell aggregation].

Data from literature concerning cell aggregation induced by various substances are considered. The biochemical nature of cell aggregation inducers, participation of membrane receptors in this process, biochemical aspects and practical significance of the cell aggregation process are discussed.

Animals↗
PubMed1977

Nevus cell aggregates associated with lymph nodes: estimated frequency and clinical significance.

Aggregates of cells resembling those of cutaneous nevi have been found in the capsules of lymph nodes. Although seemingly rare, this extraordinary lesion could conceivably occur often enough to be more than a pathological curiosity, and should be differentiated from metastatic tumor. Slides from every axillary lymph node dissection for female mammary carcinoma in the years 1964 and 1974 at Memorial Hospital were reviewed, as were slides from 100 consecutive lymph node dissections performed during 1974 in patients with malignant melanoma. Nevus cell aggregates (NCA) were associated with three of 17,504 lymph nodes (0.017%) obtained from 909 mastectomies, or 0.33% of the cases. Among the 100 lymph node dissections for malignant melanoma, NCA were found associated with three of the 2,607 lymph nodes examined (0.12%), or 3.0% of the cases studied. Since NCA occur in association with lymph nodes more often than previously thought, the possibility that they may be a potential source of malignant melanoma in patients without a demonstrable cutaneous or mucosal primary is discussed.

Axilla↗