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Biomedical subjects

L Orci

Publications and source records attributed to L Orci.

At least 325 records · Page 18Linked to original sources
PubMed1981

Primitive islets contain two populations of cells with differing glucagon immunoreactivity.

Immunofluorescence staining with insulin, glucagon, and somatostatin antisera revealed different immunoreactive cell types in the pancreatic islets of the ratfish. In particular, one cell type was present that reacted with C- and N-terminal anti-glucagon sera, while another type was only detected by N-terminal anti-glucagon sera. The latter cell, however, became reactive to C-terminal anti-glucagon after proteolytic treatment of the section. A similar cell type was found in the epithelium of the pancreatic duct and of the gastrointestinal mucosa. The data indicate that among glucagon immunoreactive cells, some cells situated exclusively in the pancreas possess both C- and N-terminal glucagon immunoreactants, while in other pancreatic as well as intestinal cells, the sequence that binds C-terminal anti-glucagon serum appears masked and becomes accessible to the antibody only after proteolytic digestion.

Animals↗
PubMed1980

Opposite polarity of filipin-induced deformations in the membrane of condensing vacuoles and zymogen granules.

Filipin binding to membrane sterols induces deformations of the membrane that are detected by freeze-fracture either as 20- to 25-nanometer protuberances or as pits on the fracture faces. By using the filipin probe in pancreatic acinar cells, it was found that the polarity of filipin-induced deformations in the membrane limiting the Golgi condensing vacuoles is opposite that in the membrane limiting the mature zymogen granules. This asymmetry could be due to unequal partitioning of cholesterol between the membrane leaflets in these two compartments during the transformation of the condensing vacuole into the zymogen granule.

Cholesterol↗
PubMed1980

Heterogeneity of toad bladder granular cell luminal membranes. Distribution of filipin-sterol complexes in freeze-fracture.

Glutaraldehyde-fixed toad urinary bladders were incubated with the sterol specific antibiotic, filipin, and the distribution of the resulting filipin-sterol complexes was studied in freeze-fracturing replicas. While the luminal membrane of some cells had a heavy, homogeneous labelling, most had clusters of filipin-sterol complexes scattered on an otherwise poorly labelled membrane. These clusters were seen to overlie cytoplasmic granules, which are found just beneath the luminal plasma membrane of this cell type, and which were always heavily labelled. These results suggest that (a) the granule membranes have a high cholesterol content and (b) sites of interaction between granule and luminal membranes might be enriched in cholesterol. In addition, filipin-sterol complexes were absent from vasopressin-induced particle aggregates on the granular cell luminal membrane.

Animals↗
PubMed1980

Gap junction development is correlated with insulin content in the pancreatic B cell.

The development of gap junctions between insulin-containing B cells was quantitatively analyzed in islets of Langerhans isolated from rats treated with the sulfonylurea glibenclamid for 1, 2, or 7 days. Glibenclamid treatment was associated with a marked depletion of the insulin content of B cells and with an increase in the number and size of gap junctions between these cells. A significance correlation was found between these two events.

Animals↗
PubMed1980

Polar redistribution of 125I-labelled insulin on the plasma membrane of cultured human lymphocytes.

Cultured human lymphocytes of the IM-9 line have specific binding sites for 125I-insulin that have been characterized in detail. When the hormone--cell interaction was studied by quantitative electron microscopic (EM) autoradiography, it was shown that initial binding was to the plasma membrane and that at 37 degrees C a small fraction of the ligand was internalized by the cell. The internalized ligand was found preferentially localized in lysosomes in the Golgi region of the cell. It is well known that di- or multivalent ligands redistribute in the plane of the membrane before internalization. We now report that following initial binding the univalent ligand insulin also undergoes a polar redistribution ('capping') before internalization.

Cell Compartmentation↗
PubMed1980

Glucagon and glicentin immunoreactivity are topologically segregated in the alpha granule of the human pancreatic A cell.

Glicentin is a 100-amino acid polypeptide purified from the porcine intestine and containing the immunodeterminants of glucagon. We have previously reported the presence of glicentin immunoreactivity in the glucagon-containing, specific secretory granules (alpha granules) of the pancreatic and gastric A cell. With an improved immunocytochemical probe, the protein A-gold (pAg) technique, we are now able to show that glucagon and glicentin-like material are topologically segregated in the alpha granule of the human pancreatic A cell.

Glucagon↗
PubMed1980

Distribution of filipin-cholesterol complexes at sites of exocytosis - a freeze-fracture study of degranulating mast cells.

The distribution of membrane cholesterol at sites of exocytosis was studied with the cytochemical probe, filipin, in freeze-fractured rat peritoneal mast cells. When degranulation was induced in mast cells by polymyxin B, the membrane of all secretory granules, as well as the plasma membrane, including bulged areas signaling incipient exocytosis, appeared heavily labeled with filipin-sterol complexes (recognizable as 25-nm protuberances). This is evidence that cholesterol depletion is not an absolute requirement for membrane fusion.

Animals↗
PubMed1980

Binding, internalization, and lysosomal association of 125I-human growth hormone in cultured human lymphocytes: a quantitative morphological and biochemical study.

125I-human growth hormone (125I-hGH) binds specifically to receptors on cultures human lymphocytes (IM-9). When this process is studied by use of quantitative EM radioautography, under conditions of incubation at 15 degrees C for 5 min, the ligand is localized to the plasma membrane of the cell. At 30 degrees and 37 degrees C, however, 125I-hGH is progressively internalized by the cell as a function of time. The internalized ligand is found predominantly in the Golgi region of the cells, with a five-fold preferential localization to membrane-bounded structures with the morphological and cytochemical characteristics of lysosomes. Up to 59% of these lysosome-like structures are positive for the acid phosphatase reaction under the conditions of incubation at 37 degrees C for 120 min. When the cell associated radioactivity after 15-120 min of incubation at 37 degrees C is extracted in 1 M acetic acid and filtered on a Sephadex G-100 column, 58-73% of the material elutes as intact hGH. When cells are incubated with 125I-hGH at 37 degrees C for 15-120 min, separated from the incubation medium, and washed and diluted 100-fold, the percent 125I-hGH dissociable decreases as a function of increasing time of incubation. When cells are incubated with 125I-hGH for 15 min at 37 degrees C and the radioactivity that dissociates from the cells during 15-90 min is studied, the labeled material appearing in the incubation medium is progressively degraded as a function of time of incubation. When the dissociation process is studied radioautographically, grains are found both in plasma membrane and intracelluar compartments after 30 min of association, but after 30 and 120 min of dissociation a higher proportion of grains are in the intracellular compartment. After 120 min of association, there is less dissociation from either compartment and a preferential increase of grains in the intracellular compartment. These data suggest that receptor-linked internalization of a polypeptide hormone provides a mechanism that couples degradation of the ligand with loss of the cell surface receptor.

Autoradiography↗
PubMed1980

Nonrandom distribution of gap junctions between pancreatic beta-cells.

The numerical and spatial distribution of gap junctions between insulin-containing cells (beta-cells) under resting and stimulated conditions of insulin secretion were quantitatively analyzed in freeze-fracture replicas of isolated rat islets of Langerhans. The results show that the beta-cells located at the periphery of the islet have twice as many gap junctions per unit membrane area as the beta-cells situated in the islet center. In both locations, gap junctions assumed a nonrandom clustering on the beta-cell membranes. During stimulation of insulin secretion, the gap junctions were found increased between the central and between the peripheral beta-cells. The degree of their clustering was also modified. The latter change depended both on the location of the gap junctions in the islet and on the type of stimulation used (high glucose or glibenclamide).

Animals↗
PubMed1980

Binding, internalization, and lysosomal association of 125I-glucagon in isolated rat hepatocytes. A quantitative electron microscope autoradiographic study.

When 125I-glucagon is incubated with freshly isolated rat hepatocytes and studied by quantitative electron microscope autoradiography, the labeled material localizes to the plasma membrane of the cell at early times of incubation of 20 degrees C; at later times of incubation at 20 degrees C, there is little further translocation of the labeled ligand. When incubations are carried out at 37 degrees C, the labeled material is progressively internalized by the cell after a brief delay. When the internalized radioactivity is further analyzed, it is found to associate preferentially with lysosome-like structures. When the cell-associated radioactivity is extracted, there is degradation of the ligand in incubations carried out at 37 degrees C. The events involved in the interaction of 125I-glucagon with the hepatocyte are similar to those previously described for labeled insulin in this cell. The process of binding, internalization, and lysosomal association appears to be a general process related to many polypeptide hormones and growth factors, and may represent the mechanism by which the specific binding of the ligand to the cell surface mediates the degradation of the ligand and the loss of its surface receptor.

Animals↗
PubMed1980

Quantitative immunocytochemical localization of pancreatic secretory proteins in subcellular compartments of the rat acinar cell.

The recently developed protein A-gold technique for the detection of intracellular antigenic sites on thin sections was utilized to localize nine different secretory proteins in the rat exocrine pancreas. Amylase, chymotrypsinogen, trypsinogen, lipase, elastase, carboxypeptidases A and B, RNase and DNase, were detected at the level of the rough endoplasmic reticulum, the Golgi area, and the zymogen granules of the acinar cells, as well as in the acinar lumen. A quantitative evaluation of the labeling showed that its intensity was not identical for all enzymes studied nor in all cellular compartments analyzed. An increasing gradient of the labeling from the rough endoplasmic reticulum to the Golgi and to the zymogen granules was found for amylase, carboxypeptidases A and B, chymotrypsinogen, trypsinogen, and RNase, while a comparable low degree of labeling in the Golgi apparatus and in the zymogen granules was observed for DNase, lipase, and elastase. These results suggest that the nine enzymes are processed through the same intracellular compartments, but that they may be concentrated to different degrees in the zymogen granules before being released in the acinar lumen.

Animals↗
PubMed1980

Morphologic probes of polypeptide hormone receptor interactions.

Polypeptide hormones, growth factors, and a variety of other naturally occurring ligands bind specifically to receptors on the cell surface. At physiologic temperatures these ligands are internalized by cells and associate intracellularly with lysosomes. Receptor-mediated internalization provides a simple mechanism that may act to couple receptor-mediated hormone degradation with receptor-medicated receptor regulation.

Animals↗