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Biomedical subjects

M Tavassoli

Publications and source records attributed to M Tavassoli.

At least 199 records · Page 11Linked to original sources
PubMed1982

Biphasic uptake of iron-transferrin complex by L1210 murine leukemia cells and rat reticulocytes.

The kinetics of the cellular uptake of iron-transferrin complex was studied in L1210 murine leukemia cells and rat reticulocytes using 125I-transferrin. Saturation of transferrin with iron was necessary for optimal uptake. Following the incubation of cells with the radiolabeled complex a biphasic pattern of uptake was observed. The initial phase was rapid and relatively temperature-independent and was not altered by ethylamine, an inhibitor of transglutaminase activity which is necessary for receptor-mediated endocytosis. This phase was considered to result from receptor-ligand interaction which could be reversed to a great degree by replacement with unlabeled transferrin. A plateau was then reached, indicating a saturation of receptors. After 30 min a second phase of uptake was indicated by the second rise in the curve. This phase was slow, relatively temperature-dependent and could be abolished by ethylamine. It was interpreted as evidence of internalization of the ligand. Analysis of the data from competition studies with unlabeled transferrin indicated that the first phase might itself comprise a reversible and an irreversible step with a ratio of 5 to 1.4 for bound transferrin. Thus, the cellular uptake of iron-transferrin complex may consist of a reversible ligand-receptor interaction. Conformational changes may render this interaction irreversible and the internalization of the ligand may then follow.

Animals↗
PubMed1982

Morphological studies on long-term culture of marrow cells: characterization of the adherent stromal cells and their interactions in maintaining the proliferation of hemopoietic stem cells.

In long-term cultures of bone marrow, the adherent stromal cells provide support for the proliferation and maintenance of hemopoietic stem cells. These stromal cells and their interactions were characterized by means of scanning (SEM) and transmission (TEM) electron microscopy in correlation with functional studies. Cultures were initiated by establishing the adherent stromal layer as a "soil" which was then "seeded" after 3 weeks by the addition of another marrow-cell suspension. Clonal assay of the supernatant demonstrated the continuous proliferation of the hemopoietic stem cell. The stroma essentially consisted of two cell types, macrophages and epithelioid cells. Macrophages were smaller, 10-15 microns, phagocytosed latex and carbon particles, and contained lysosomes. Their surface did not stain with polycationic ferritin (PCF). Epithelioid cells were much larger, more than 100 microns; contained numerous thin, elongated mitochondria; did not phagocytose latex particles; but did display strong surface staining with PCF. The appearance of epithelioid cells in TEM depended on their state of development and whether the section was parallel or perpendicular to the substratum. Epithelioid cells displayed a maturational spectrum, at two ends of which were synthetic and storage phases. In the synthetic phase, the cell contained numerous profiles of rough endoplasmic reticulum, and in the storage phase, numerous storage granules. These two phases were best appreciated in sections perpendicular to the substratum, demonstrating synthetic cells on top settling over the substratum upon maturation into the storage cells. Both macrophages and epithelioid cells contained fat globules which increased in number and size with the addition of hydrocortisone to the culture medium. A distinct fat-cell type, as has been claimed, was not found in this study. Granulopoiesis was observed in the culture system in the absence of colony-stimulating activity in the supernatant, suggesting direct cellular interaction or short-range factors in the induction of granulopoiesis. Widespread cellular interactions were noted between macrophages and epithelioid cells, the latter often completely embracing the former and both extending cytoplasmic processes toward each other. This is reminiscent of the cooperative interaction of endoderm and mesoderm in chick embryo hemopoiesis and may be necessary for the maintenance of stem cells in these cultures.

Animals↗
PubMed1982

Lanthanum as an electron microscopic stain.

Applications of lanthanum as an electron microscopic tracer have been reviewed. This electron-dense trivalent cation, which binds avidly to calcium binding sites, can be used as tracer for delineating extracellular spaces and intercellular junctions. It has served as a basis for classification of junctional structures. It can also be used as a calcium probe, a tracer in studying the permeability of barriers, as an intracellular marker and as an electron microscopic stain for such membrane components as surface glycoprotein. Each of these applications may require a different methodology. Thus methodological considerations in the use of this tracer have also been reviewed. The recent recognition that lanthanum is more than a passive tracer and that by reacting with different cell components may serve as a true stain, will extend the use of lanthanum in electron microscope histochemistry.

Animals↗
PubMed1982

Production of a colony-inhibitory factor by ethylamine in continuous, long-term marrow culture.

The effect of ethylamine (EA), a simple alkylamine, on continuous, long-term marrow culture was studied in the mouse. EA reduced the granulocyte-monocyte progenitor cell (CFU-c) activity in the supernatant of these cultures in a dose-dependent fashion. This inhibitory effect persisted even after the EA was completely removed from the culture. Moreover, the cell-free supernatant showed inhibitory activity on the growth of CFU-c using freshly isolated target cell. This inhibitory effect also persisted after the EA was completely removed from the culture. Thus, EA appeared to induce changes in these cultures not only by interfering with their potential to maintain the CFU-c but also by releasing a factor in the supernatant that was inhibitory to the CFU-c growth derived from fresh bone marrow. Electron microscopy indicated profound alterations in lysosomal structures. The selective accumulation of this weakly basic substance in the lysosomes may lead to elaboration and release of a colony-inhibitory factor in the supernatant. This effect of EA appears to be independent of its effect on receptor-mediated endocytosis.

Animals↗
PubMed1982

Radiosensitivity of stromal cells responsible for in vitro maintenance of hemopoietic stem cells in continuous, long-term marrow culture.

Marrow stromal cells are generally thought to be radioresistant. However, when the marrow was irradiated in vivo or in vitro before its use for the continuous long-term marrow culture, doses of radiation as low as 500 rad interfered with the establishment of the adherent stromal layer. Moreover, when the stromal layer was permitted to establish, similar doses of radiation interfered with its potential to support the proliferation and maintenance of the hemopoietic stem cell. Thus, marrow stromal cells appear to be more radiosensitive than hitherto thought. The type of damage may vary, however, according to the dose of radiation. Small doses may interfere with such functions as adhesion or cell division while larger doses may completely destroy the cell.

Animals↗
PubMed1982

Anemia of spaceflight.

A consistent deficit in the red cell mass has been observed during both the American and Soviet orbital space flights and is sometimes referred to as "astronaut anemia." This may be associated with a reduction in plasma volume so that the hematocrit and the hemoglobin concentration remain unchanged. During the Gemini program, the hypobaric hyperoxic atmosphere of the spacecraft led to oxidative injury to the red cells, causing hemolysis. Thus, the atmosphere proved to be, in part, responsible for the deficit. However, a similar deficit of a lesser magnitude was again observed in subsequent flights with normal ambient PO2 as well as in the Soviet flights in which an atmosphere essentially of see level air is used. The cause of this deficit seems to be suppression of erythropoiesis, as indicated by reticulocytopenia and erythroid hypoplasia of the marrow. No suppression of erythropoiesis has been observed in ground-based experiments carried out under almost identical conditions. Thus, the suppression of erythropoiesis is thought to be related to weightlessness. The reason for the suppression is not known but may be related to total inhibition of bone formation.

Aerospace Medicine↗
PubMed1982

Ultrastructural and radiobiological characterization of stromal cells in continuous, long-term marrow culture.

Hemopoietic stromal cells were studied in continuous, long-term marrow culture. A correlative study was carried out involving cytochemistry as well as scanning (SEM), and transmission electron microscopy (TEM) with sections cut either perpendicular or parallel to the substratum. Only two stromal cell types were identified: epithelioid cells and macrophages. The appearance of these cells, however, varied according to their topography in the culture and the method of observation; a finding that may explain the multiplicity of the cell types reported in these cultures. The two cell types displayed considerable interconnections and interactions which may be essential in their support function for the proliferation and maintenance of hemopoietic stem cells. They also demonstrated numerous coated pits and vesicles suggestive of extensive receptor-mediated endocytosis. Stromal cells, generally thought to be relatively radioresistant, demonstrated hitherto unrecognized radiosensitivity in culture. Doses of radiation as low as 500 rads interfered with their support function for the maintenance of the hemopoietic stem cell.

Animals↗
PubMed1981

Acid phosphatase activity in the cytosol fraction of the breast cancer tissue.

Acid phosphatase activity was studied in the cytosol fraction of breast cancer tissue. Serum, plasma, and extracts of leukocyte and platelet were used for reference. The breast cancer tissue fraction had an electrophoretic mobility intermediate to leukocyte-derived bands 2 and 4 and corresponding to the platelet-derived band 3. The enzymes derived from platelet and breast cancer tissue were both inhibited by L-tartrate and showed a similar pattern for preferred substrates. By contrast, the breast cancer tissue-derived enzyme was different from the enzyme fraction responsible for the elevated serum enzyme activity in some patients with disseminated breast cancer. The two fractions could be distinguished by electrophoretic mobility and tartrate sensitivity. These findings substantiate our previous report, which suggested that the fraction responsible for elevated serum enzyme activity in the course of breast cancer is not derived from cancer tissue. It is proposed that the osteolysis, resulting from bone metastases, may be responsible for elevated serum enzyme activity in this disease.

Acid Phosphatase↗
PubMed1981

Migration of entire megakaryocytes through the marrow--blood barrier.

Electron microscopic evidence is presented to indicate that entire megakaryocytes traverse the marrow--blood barrier and enter the circulation. Passage occurs through apertures of 6 micrometer in diameter, located in the parajunctional areas of the marrow sinus endothelium. Serial sectioning indicates that these apertures are transendothelial rather than interendothelial. The cytoplasm of these megakaryocytes form sinuating elongated projections which may release their platelets in the sinus lumen or when reaching the pulmonary circulation. In the extravascular compartments, megakaryocytes are preferentially located in the subendothelial region. In this location they can send numerous organelle-free projections into the lumen. These projections distinguishable from less numerous organelle-containing projections could serve to 'anchor' the cell to the endothelium. They could also serve to 'monitor' the circulation and to receive information as to the requirement of body for platelet formation.

Animals↗
PubMed1981

Dynamics of red cell egress from bone marrow after blood letting.

To study the dynamics of red cell egress from the marrow, the demand for red cell delivery was enhanced in splenectomized rats by removing 25% of the blood volume, which was then immediately replaced by plasma. Within 15 min, packed cell volume declined by 22% of the initial value. Corrected reticulocyte count followed a biphasic pattern: an initial peak amounting to 26% occurred within 4-6 h followed by a more marked peak after 48 h. Quantitative electron microscopy of the marrow sinus wall indicated significant increases in the numbers of reticulocytes and leucocytes in transit after 5 h. Vesicles containing a flocculant substance were seen in the endothelium. The vesicles could cause segmental destabilization of endothelium, providing suitable areas for cell migration. There was also a significant reduction in the mean length of the overlapping segments of the endothelial cells, suggesting that these cells slid over one another to increase the luminal calibre. Within the rigid confines of bones where the marrow volume is fixed, this increase may lead to the displacement of mature haemopoietic cells into the lumen and whence into the circulation.

Animals↗
PubMed1981

OTO method for preservation of actin filaments in electron microscopy.

Osmium tetroxide, commonly used as a fixative in electron microscopy, can destroy actin filaments. Thiocarbohydrizide (TCH) is a bipolar substance that binds to the osmium. By sandwiching TCH between two phases of osmium treatment, tissue exposure to osmium could be minimized without destroying actin filaments. The contrast of osmophilic components of cells was also enhanced.

Actins↗