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Biomedical subjects

L Orci

Publications and source records attributed to L Orci.

At least 307 records · Page 17Linked to original sources
PubMed1981

Co-culture of nerve cells and pancreatic islets.

Nerve cell dissociated from the cerebral cortex of mice were co-cultured with isolated pancreatic islets of Langerhans. After two weeks of co-culture, numerous axons had invaded the islets and differentiated nerve endings were closely juxtaposed to the endocrine islet cells. In contrast, no remnants of nerve cells were observed in isolated islets cultured alone for the same duration. The attachment and/or survival and differentiation of nerve cells were markedly promoted in the presence of islets. The latter effects were probably due to insulin secreted by the islets in the culture medium.

Animals↗
PubMed1981

Glucagon degradation in isolated rat hepatocytes: effect of ammonium chloride and chloroquine.

It has recently been shown that, when [125I]glucagon is incubated with isolated rat hepatocytes at 37 degrees, the radiolabeled material is progressively internalized by the cell and is found to associate preferentially with lysosome-like structures. To assess the role of this process in the degradation of the hormone, the degradation of [125I]glucagon by isolated rat hepatocytes was examined both in incubation media and in cell extracts, after exposure of the radiolabelled hormone to hepatocytes in the absence and in the presence of lysosomotropic agents NH4Cl (8 mmoles/l) or chloroquine (10 micromoles/l); bacitracin (0.8 mg/ml, i.e. 0.6 mmoles/l) was present in all experimental conditions to minimize extracellular degradation. Neither NH4Cl nor chloroquine altered the time course and steady-state binding of [125I]glucagon, or the degradation of the hormone in incubation media. However, both agents partially inhibited the degradation of cell-associated [125I]glucagon in steady-state conditions. In dissociation experiments, NH4Cl, and even more so chloroquine, decreased the rate and the extent of release of radiolabelled material from the cells. Moreover, after 60 min dissociation, the presence of either agent resulted in less degradation of both cell-associated [125I]glucagon and that released into the medium. These results suggest that lysosomes are involved in the intracellular degradation of glucagon.

Ammonium Chloride↗
PubMed1981

Stretch induces granule exocytosis in toad urinary bladder.

Evidence from this sections and freeze-fracture is presented showing that stretch induces a burst of exocytosis in granular cells of the toad urinary bladder epithelium. Since the role of granule exocytosis in hormonally-induced permeability changes in this tissue has not yet been clarified, we propose that the stretch factor is an important parameter to consider and standardise in future physiological and morpho-functional studies using this model transporting system.

Animals↗
PubMed1981

Heterogeneous distribution of filipin--cholesterol complexes across the cisternae of the Golgi apparatus.

The Golgi apparatus is a key element in the ordered movement of secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane during secretion. It has been shown that cisternae that receive membranes from the reticulum are morphologically similar to the latter and that cisternae liberating secretory granules resemble that plasma membrane. By using an ultrastructural probe for membrane cholesterol, filipin, on freeze-fractured and thin-sectioned exocrine and endocrine pancreatic cells, we have shown that an enrichment in filipin-cholesterol complexes takes places across the stacked cisternae of the Golgi apparatus; the reticulum-related (forming) cisternae are poor in such complexes, but the secretory granule-related (maturing) cisternae contain numerous complexes. Secretory granule membrane is also richly labeled with filipin-cholesterol complexes. The heterogeneous cholesterol distribution in the membranes of the Golgi apparatus, as shown by filipin, emphasizes the polarity of this organelle, in agreement with its role in organizing the traffic of the secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane.

Animals↗
PubMed1981

Insulin immunoreactive sites demonstrated in the Golgi apparatus of pancreatic B cells.

Insulin immunoreactive sites were localized in the Golgi apparatus of pancreatic B cells by light and electron microscopy. Identification of the Golgi apparatus by immunofluorescence required the prior degranulation of B cells with glibenclamide to reduce the insulin immunostaining due to secretory granules. In such cells, insulin immunofluorescence revealed brightly stained, crescent-shaped strands with form and location super-imposable on that of Golgi complexes seen in thin sections of the same cells. With the electron microscope, the insulin immunoreactive sites revealed by the protein A/gold technique were localized in the cisternae and vesicles of the Golgi apparatus of glibenclamide-treated and control B cells and over maturing and mature secretory granules. The quantitative evaluation of the intensity of the insulin immunoreactive sites in the Golgi apparatus revealed a density of sites 4 times more than cellular background values. The demonstration of insulin immunoreactivity in the Golgi apparatus provides direct evidence for the involvement of this compartment in the transport and maturation of proinsulin into insulin.

Animals↗
PubMed1981

Surface redistribution of 125I-insulin in cultured human lymphocytes.

The cultured human lymphocyte (IM-9) binds 125I-insulin by a receptor-mediated process; the receptor, in turn, is regulated by the ligand. In the present study we have examined quantitatively the morphologic events involved in 125I-insulin interaction with the surface of the lymphocyte. At 2 min of incubation of 15 degrees or 37 degrees C, the ligand localizes preferentially at the villous surface of the cell, whereas with longer periods of incubation, the ligand distributes indistinguishably between the villous and nonvillous surface. When rebinding is blocked, 125I-insulin localizes preferentially at the nonvillous surface of the cell. When the total cell surface is considered, there is little preferential association with coated pits; when only the nonvillous surface is considered, a preferential association with coated pits is found and is quantitatively increased in the absence of rebinding of the ligand. This cell has an abundant villous surface (approximately 55% of the total surface); and, as seen on freeze-fracture replicas, the plasma membrane of the villous surface contains a 60% greater density of intramembrane particles than the nonvillous surface. The data suggest an ordered pattern of insulin interaction with the cell surface (i.e., binding to villi followed by redistribution to the nonvillous portion of the cell containing coated pits). These events probably reflect the mechanism by which the cell segregates specific receptors and related proteins in the plane of the membrane so that they can be selectively removed.

Cells, Cultured↗
PubMed1981

Application of the protein A-gold technique for electron microscopic demonstration of polypeptide hormones.

The protein A-gold (pAg) technique enables the electron microscopic detection of antigenic material on thin sections of aldehyde-fixed and Epon-embedded tissue. Application of this technique to the endocrine pancreas and gastrointestinal mucosa using antisera against insulin, glucagon, somatostatin, pancreatic polypeptide, gastrin, and neurotensin allowed these polypeptides to be localized in the secretory granules of the corresponding specific cell types. The small size of marker gold particles permitting the precise identification of the labeled organelles coupled to the high specificity of the binding represent further evidence that the protein A-gold technique can be used as a general cytochemical reagent for the visualization of antigen-bound antibodies on thin sections.

Animals↗
PubMed1981

The fate of [125I]iodoepidermal growth factor in isolated hepatocytes: a quantitative electron microscopic autoradiographic study.

When [125I]iodoepidermal growth factor is incubated with freshly isolated rat hepatocytes, cell-associated radioactivity reaches apparent steady state by 60 min at 20 C and by 30 min of incubation at 37 C. When the distribution of cell-associated radioactivity is studied at different times of incubation by quantitative electron microscopic autoradiography, the ligand initially associates with the plasma membrane and is progressively internalized as a function of time. The internalized ligand preferentially associates with lysosome-like structures. Qualitatively, these events are similar to those previously obtained with labeled insulin and glucagon in this cell, but quantitatively, the internalization of epidermal growth factor is much greater. The data suggest that the ligand or its specific receptor rather than the cell type is the major determinant of the rate of internalization.

Animals↗
PubMed1981

Structural heterogeneity of endocytic membranes in macrophages as revealed by the cholesterol probe, filipin.

The polyene antibiotic, filipin, by specifically interacting with cholesterol, produces approximately 25-nm protuberances (filipin-sterol complexes) in freeze-fractured membranes, and the addition of filipin to aldehyde fixatives has been recently introduced as a cytochemical technique for the localization of cholesterol in cell membranes. In a previous study we showed that, in fibroblasts filipin-sterol complexes are absent from endocytic coated pits. To establish whether the absence of filipin-sterol complexes is a phenomenon restricted to coated pits or is correlated with endocytosis in general, we applied the filipin probe to cultured mouse peritoneal macrophages, in which different forms of endocytosis take place. The macrophages were incubated with bovine albumin or concanavalin A (Con A) to induce pinocytosis, and with heat-killed straphylococci or opsonized erythrocytes to induce phagocytosis, then fixed in glutaraldehyde/filipin and freeze-fractured. Filipin-sterol complexes were plentiful on the plasma membrane, on the smooth-membrane invaginations and vesicles induced by albumin, on the large endocytic vacuoles induced by Con A, and on the membrane of phagosomes but, in contrast, they were absent from coated pits and vesicles, as well as from coated segments of invagination or vesicles. These results indicate that the membranes involved in different types of endocytosis do not react in the same way with filipin and may, therefore, have a different cholesterol content. This could reflect different mechanisms of formation for the various types of endocytic vesicles.

Animals↗
PubMed1981

Immunochemical characterization and distribution of calcitonin in the lizard.

Immunological and chromatographic methods were used to investigate the distribution of calcitonin (CT) in various tissues of Lacerta muralis, a common wall lizard. Salmon CT-like immunoreactivity was found in high concentration in extracts of ultimobranchial gland (UBG) and in significant amounts in lung and brain extracts, but not in other tissues (oesophagus, stomach, duodenum, liver, skin, muscle and thyroid). Serial dilution of UBG, lung and brain extracts gave parallel displacement curves to that of synthetic salmon CT (sCT), but no reactivity was found in the human CT assay. On Sephadex G-50, UBG, lung and brain extracts contained an sCT-like immunoreactive peak which co-eluted with synthetic sCT. However, on high performance liquid chromatography (HPLC) the sCT-like peak in UB, lung and brain extracts eluted 2 ml later than synthetic sCT. This paper describes the first immunochemical characterization of CT in the UBG of the lizard, demonstrates the distribution of extra-ultimobranchial CT and throws some light on the evolution of the calcitonins.

Animals↗
PubMed1981

Demonstration of glucagon in the stomach of human fetuses.

Electron microscopy using antiglucagon or antiglicentin antisera and the protein A-gold (pAg) technique revealed a population of immunoreactive cells in the gastric mucosa of human fetuses. The secretory granules of these cells showed the same ultrastructural characteristics and the same labeling pattern as pancreatic alpha-granules. These data demonstrate that the stomach of human fetuses contains cells with secretory granules indistinguishable by morphologic and immunocytochemical criteria from the pancreatic A-cells.

Cytoplasmic Granules↗