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Biomedical subjects

L Orci

Publications and source records attributed to L Orci.

At least 379 records · Page 21Linked to original sources
PubMed1979

The role of the cytoskeleton in pancreatic B-cell function.

The ultrastructural organization of B-cell microtubular-microfilamentous system, its alteration by several pharmacological agents and the concomitant changes in the dynamics of insulin release, the biochemical characterization of islet tubulin and actin, the involvement of microtubules in the process of proinsulin biosynthesis and conversion, the analysis of motile events in endocrine pancreatic cells, the possible participation of microtubular-microfilamentous structures in cell surface organization of the B-cell, and the anomaly of the microtubular apparatus in certain pathological conditions are reviewed. The experimental data support the view that microtubules and microfilaments play an essential role in the process of insulin synthesis and release, as well as in the mechanism of glucagon secretion.

Animals↗
PubMed1978

[Interaction of epidermal growth factor with human fibroblasts in culture: an autoradiographic study at the ultrastructural level].

The potent mitogen epidermal growth factor (EGF) binds to specific receptors on human fibroblasts. In the present study we have used a quantitative EM autoradiographic approach to visualize the events involved in the binding process. When 125I-EGF is incubated at 4 degrees C for 120 min, labeled EGF primarily localizes to the plasma membrane of the fibroblast but when incubated at 37 degrees C for 120 min., over 2/3 of the labeled material is internalized by the cell. The internalized radioacitivity is primarily localized to lysomes. These studies demonstrate a temperature-dependent internalization of EGF following initial binding to specific plasma membrane receptors.

Cell Membrane↗
PubMed1978

Intracellular translocation of iodine-125-labeled insulin: direct demonstration in isolated hepatocytes.

Insulin labeled with iodine-125 binds to receptors on isolated rat hepatocytes. At low temperatures initial binding is restricted to the plasma membrane as detected by direct quantitative autoradiographic analysis with the electron microscope. With increasing time and temperature of incubation there is a systematic and progressive translocation of autoradiographic grains to a highly limited area of the cell periphery representing no more than 15% of the radius of the cell.

Animals↗
PubMed1978

Rod-shaped particles in the plasma membrane of the mitochondria-rich cell of amphibian epidermis.

A freeze-fracture study has revealed rod-shaped intramembranous particles on the plasma membrane P-face (cytoplasmic leaflet) of the mitochondria-rich cell (or flask cell) of Xenopus laevis and Rana ridibunda epidermis. Such particles have previously been found in all other mitochondria rich cells examined by this technique, namely, the MR-cell of toad bladder epithelium, the dark cell of rat kidney collecting tubule, and the flask cell of Xenopus kidney collecting tubule. These particles are assumed, therefore, to be closely connected with the function of this cell type.

Animals↗
PubMed1978

Virus-induced diabetes in mice: a quantitative evaluation of islet cell population by immunofluorescence technique.

The endocrine cell populations of pancreatic islets in encephalomyocarditis (EMC)-virus infected mice were assessed quanititatively by immunofluorescence using specific antisera against 4 islet hormones. A marked reduction of the volume of insulin-containing (B-) cells (up to one tenth of control values) was observed at all stages studied in the hyperglycaemic mice. This was accompanied by the inversion of the normal ratio between B- and non B-cells. The volume of the latter cell types was also modified at different time points after infection: glucagon-cells were augmented 14 days after infection; PP-cells were decreased 2--3 days and 21 days after infection; somatostatin-cells decreased to one-fourth of control values in hyperglycaemic animals 21 days after infection. The latter results suggest that non B-cells are also involved in islet reaction to virus infection.

Animals↗
PubMed1978

Epidermal growth factor: morphological demonstration of binding, internalization, and lysosomal association in human fibroblasts.

Using a quantitative electron microscopic autoradiographic technique, we have localized the initial binding step of 125I-labeled epidermal growth factor (125I-EGF) to the plasma membrane of the human fibroblast. After initial binding, labeled EGF is internalized progressively by the cell in a time- and temperature-dependent fashion; when cell-associated radioactivity comes to steady state, approximately 1/3 of the autoradiographic grains are related to the plasma membrane and approximately 2/3 have been internalized. Under these conditions the internalized grains are almost exclusively related to lysosomal structures. When 125I-EGF associates with the cells for 2 hr at 4 degrees or 2 min at 37 degrees, 34% of grains localize to coated regions of the membrane. These coated regions make up less than 2% of the membrane surface. These data directly confirm kinetic studies and suggest that saturable binding of EGF is followed by adsorptive pinocytosis and cellular degradation of the ligand and possibly its cell surface receptor.

Autoradiography↗
PubMed1978

A freeze-fracture study of membrane events during neurohypophysial secretion.

Freeze-fracture was used to study the membrane events taking place during neurosecretory granule discharge (exocytosis) and subsequent membrane internalization (endocytosis) in axons of neurohypophyses from control and water-deprived rats. En face views of the cytoplasmic leaflet (P face) of the split axolemma reveal circular depressions that represent the secretory granule membranes fused with the plasma membrane during exocytosis. These depressions often contain granule core material in the process of extrusion into the extracellular space. The membrane surrounding some of the exocytotic openings shows a decreased number of intramembrane particles (mean diameter, 8 nm) which are elsewhere more numerous and evenly distrubuted on the fracture face. Endocytotic sites appear as smaller plasma membrane invaginations, with associated intramembrane particles. Moreover, such invaginations often contain large particles (mean diameter, 12 nm) that appear as clusters on en face views of the membrane leaflet. Quantitative analysis indicates that the number of exocytotic images increases significantly in glands from water-deprived rats. Concomitantly, the number of endocytotic figures per unit area of membrane is raised as is the number of clusters of large particles. The observations demonstrate that, in the neurohypophysis, it is possible to distinguish exocytosis morphologically from endocytosis and that the two events can be assessed quantitatively.

Animals↗
PubMed1978

125I-insulin binding to cultured human lymphocytes. Initial localization and fate of hormone determined by quantitative electron microscopic autoradiography.

Morphologic and biochemical studies indicate that the initial action of insulin is binding to a cell surface receptor. Whether further translocation of the hormone, or a product of the hormone, occurs is unclear and has not been investigated by direct means. To determine the fate of 125I-insulin bound to its receptor, we have examined the distribution of radioactivity by quantitative electron microscopic autoradiography. Cultured lymphocytes of the IM-9 cell line were incubated with 0.1 nM 125I-insulin at 15 degrees and 37 degreesC for incubation periods extending from 2 to 90 min. At 15 degreesC, grains localize to the plasma membane and there is no translocation as a function of time. At 37 degreesC, grains predominantly localize to the plasma membrane but there is a small shift in distribution to a distance of 300-700 nm from the plasma membrane. This small additional band component of irradiation extends to approximately to10--15% of the cell radius. When a morphometric analysis is applied to grains extending 300 nm and beyond from the plasma membrane, we find no preferential localization to any intracellular organelle. We interpret these data to indicate that in the cultured lymphocyte, labeled insulin initially localizes to the plasma membrane but as fuanction of time and increasing temperature there is a small but definite translocation of the hormone or a product of the hormone to a hihgly limited aea of the cell periphery.

Autoradiography↗
PubMed1978

Ultrastructural localization of intracellular antigens by the use of protein A-gold complex.

An immunocytochemical technique for the demonstration of intracellular antigens (secretory proteins) on thin sections is reported. Staphylococcal protein A which reacts with the Fc fragment of IgG molecules was labeled with colloidal gold as a marker. The antigenic sites were visualized on aldehyde-fixed and Epon-embedded tissue in a two step procedure. The specific antisera were applied to thin sections for binding to the antigens and then visualized by the protein A-gold complex. By using this technique different secretory proteins of the exocrine and endocrine pancreas were localized. The protein A-gold technique is proposed as a general method for visualization of antigenic sites on thin sections.

Animals↗
PubMed1978

Changes in somatostatin concentration in pancreas and other tissues of streptozotocin diabetic rats.

Changes in immunoreactive somatostatin were examined in islets, whole pancreas, stomach, and hypothalamus of streptozotocin-diabetic rats. There was no change in islet somatostatin content at 2 days after the administration of streptozotocin, but thereafter, somatostatin progressively increased in the diabetic animals by 45% at 2 weeks, 230% at 6 weeks, and 500% by 6 months. By contrast, islet glucagon rose acutely and maintained a constant 2-fold elevation irrespective of the duration of the diabetes. Morphometric analysis of the somatostatin- and glucagon-producing cells in the islets revealed an apparent augmentation of both cell types. The concentration of somatostatin per total pancreas was also increased in the diabetic animals, suggesting that the islet increase was part of a true increase in pancreatic somatostatin. Pancreatic glucagon was unchanged despite the islet increase. The increase in pancreatic somatostatin was paralleled by an elevation in gastric somatostatin concentration, implying a common mechanism in response to streptozotocin for the somatostatin cells in these two sites. There was no change in hypothalamic somatostatin concentration. Islet somatostatin was also increased in alloxan-diabetic rats. suggesting that streptozotocin does not stimulate the D cells directly.

Alloxan↗