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L Orci

Publications and source records attributed to L Orci.

At least 361 records · Page 20Linked to original sources
PubMed1979

Inhomogeneity of surface labelling of B-cells at prospective sites of exocytosis.

Using ferritin-labelled Ricinus communis agglutinin to detect lectin-binding sites of the pancreatic B-cell surface, we show that limited regions of the plasma membrane are deprived of lectin-binding sites over marginated secretory granules. Such deprived regions increased during glucose stimulation of B-cells in monolayer culture: 56 +/- 8 of them were found in high (300 mg/100 ml) glucose as compared to only 27 +/- 5 in low (50 mg/100 ml) glucose (p less than 0.005). In addition, non-membrane, intracytoplasmic bridges were detected between the plasma membrane and the membrane of the marginated granule suggesting the involvement of cell web components in promoting the change in surface labelling.

Animals↗
PubMed1979

Identification of a lobe in the adult human pancreas rich in pancreatic polypeptide.

Systematic sampling of human necropsy pancreases has revealed that pancreatic polypeptide (PP) cells are not distributed equally in the gland. PP-cells are the most abundant cell type in the posterior part of the pancreatic head while they are scarce or absent in the remainder of the gland. The PP-rich part of the head can be separated by blunt dissection from the pancreas as a discrete lobe. This lobe probably originates from the ventral pancreatic bud during embryogenesis. A quantitative study of the immunofluorescent endocrine cell types (insulin, glucagon, somatostatin and pancreatic polypeptide cells) in PP-rich and PP-poor regions of pancreases in 8 subjects with ages ranging from 33 fetal weeks to 80 years, showed that the proportions of the cell types were different in youngs and adults.

Adult↗
PubMed1979

Relationship of binding to internatlization of 125I-insulin in isolated rat hepatocytes.

By quantitative electron microscopic autoradiographic technique, we have previously shown that 125I-insulin initially localizes to the plasma membrane of isolated rat hepatocytes and is subsequently internalized in a limited region of the peripheral cytoplasm. In the present study, we have shown that when cells are incubated at 20 degrees C, steady state binding is reached by 60 minutes and maintained up until 120 minutes of incubation while at 37 degrees C steady state binding is reached by 10 minutes and maintained for 30 minutes. Under both of these conditions, internalization of the labelled material occurs as a constant function of the binding. These data suggest that under normal conditions the binding of the ligand is an important rate limiting determinant of the internalization process.

Animals↗
PubMed1979

Absence of filipin-sterol complexes from large coated pits on the surface of culture cells.

Monolayer cultures of normal or transformed fibroblasts and of liver cells fixed in a glutaraldehyde solution containing 300 microM filipin, a sterol-specific polyene antibiotic, were freeze-fractured to study the distribution of cholesterol within their plasma membranes. Filipin-sterol complexes, recognizable as 25- to 30-nm protuberances scattered in the fracture face of plasma membrane, were absent from invaginations corresponding to large, bristle-coated pits (and possibly also from small, flask-shaped invaginations). These results suggest that invaginating regions on the cell surface are specialized plasma membrane domains with a lower cholesterol content than the surrounding membrane. The localized change in membrane fluidity due to the low cholesterol concentration could play a role in endocytosis.

Animals↗
PubMed1979

Intracellular localization of 125I-labeled insulin in hepatocytes from intact rat liver.

We have shown that 125I-labeled insulin initially localizes to the plasma membrane of isolated rat hepatocytes. The ligand is subsequently internalized and preferentially localizes to lysosomal structures. Further, we have observed that labeled insulin localizes to regions of the cell rich in lysosomal and Golgi elements. In the present study in intact rat liver we found that, approximately 10 min after a pulse injection of 125I-labeled insulin, 56% of the label was internalized by the cell. When all grains are considered there is a preferential localization of grains to the biliary pole of the cell and these grains are almost all internalized and preferentially associated with lysosomes. These data, therefore, demonstrate that the lysosome-Golgi-rich area of the isolated hepatocyte corresponds to the biliary pole of the cell and there is a movement of the labeled hormone from its initial binding site on the plasma face of the cell membrane toward the biliary pole of the cell.

Animals↗
PubMed1979

Parathyroid hormone biosynthesis. Correlation of conversion of biosynthetic precursors with intracellular protein migration as determined by electron microscope autoradiography.

The formation of parathyroid hormone (PTH) in the parathyroid gland occurs via two successive proteolytic cleavages from larger biosynthetic precursors. The initial product coded for by PTH mRNA is pre-proparathyroid hormone (PreProPTH), a polypeptide of 115 amino acids. Within 1 min of synthesis, the polypeptide, proparathyroid hormone (ProPTH), is formed as a result of the proteolytic removal of the NH2-terminal 25 amino acids from Pre-ProPTH. After a delay of 15-20 min, the NH2-terminal six-amino acid sequence of ProPTH is removed to give PTH of 84 amino acids. To investigate the subcellular sites in the parathyroid cell where the biosynthetic precursors undergo specific proteolytic cleavages, we examined, by electron microscopy autoradiography, the spatiotemporal migration of autoradiographic grains and, by electrophoresis, the kinetics of the disappearance of labeled Pre-ProPTH and the conversion of labeled ProPTH to PTH in bovine parathyroid gland slices incubated with [3H]leucine for 5 min (pulse incubation) followed by incubations with unlabeled leucine for periods up to 85 min (chase incubations). By 5 min, 85% of the autoradiographic grains were confined to the rough endoplasmic reticulum (RER). Autoradiographic grains increased rapidly in number in the Golgi region after 15 min of incubation; from 15 to 30 min they migrated within secretory vesicles still in the Golgi region and then migrated to mature secretory granules outside the Golgi area. Electrophoretic analyses showed that Pre-ProPTH disappeared rapidly (by 5 min) and that conversion of ProPTH to PTH was first detectable at 15 min and was completed by 30 min. At later times of incubation (30-90 min), autoradiographic grains within the secretion glanules migrated to the periphery of the cell and to the plasma membrane, in correlation with the release of PTH first detected by 30 min. We conclude that proteolytic conversion of Pre-ProPTH to ProPTH takes place in the RER and that subsequent conversion of ProPTH to PTH occurs in the Golgi complex.

Animals↗
PubMed1979

Increase of gap junctions between pancreatic B-cells during stimulation of insulin secretion.

The development of gap junctions between pancreatic B-cells was quantitatively assessed in freeze-fracture replicas of isolated rat islets under different conditions of insulin secretion. The results show that in resting B-cells, gap junctions are small and scarce but that these junctions increase when insulin secretion is stimulated. Both a short (90 min) stimulation by glucose in vitro and a prolonged (2.5 d) stimulation by glibenclamide in vivo raise the number of gap junctions; in addition, the glibenclamide stimulation causes an increase in the size of individual gap junctions. As a consequence, the total area occupied by gap junctions on the B-cell membrane and the ratio of this area to the cell volume were found significantly increased in the latter condition. The slight increase of these values observed after the glucose stimulation did not reach significance. These data indicate a change of gap junctions during the secretory activity of the pancreatic B-cells. The possibility that the coupling of the cells is affected by the treatment is discussed.

Animals↗
PubMed1979

Lysosomal association of internalized 125I-insulin in isolated rat hepatocytes. Direct demonstration by quantitative electron microscopic autoradiography.

Quantitative electron microscopic autoradiographic studies in cultured human lymphocytes and isolated rat hepatocytes have demonstrated that labeled insulin initially localizes to the plasma membrane and is subsequently internalized to a limited region of the peripheral cytoplasm. When 0.5 nm 125I-insulin is incubated with isolated rat hepatocytes, binding to the plasma membrane occurs at both 20 degrees C and 37 degrees C. Under steady-state binding conditions approximately equal to 30--40% of the labeled hormone is internalized to a distance of approximately equal to 15% of the radius of the cell. When the localization of the internalized labeled material is analyzed, by 2--5 min of incubation at 37 degrees C there is a fivefold preferential association of autoradiographic grains with lysosomal structures, and by 30--60 min of incubation at 37 degrees C there is a 10-fold preferential association. When the cell-associated radioactivity is extracted and filtered on Sephadex G-50 at each time point of incubation, radioactivity elutes predominantly in the position of 125I-insulin and is predominantly in the position of 125I-insulin and is predominantly trichloracetic acid precipitable, bindable to talc, and rebindable to liver membranes. With increasing time of association at 37 degrees C the initial rate and absolute amount of labeled material dissociable from the cell is reduced. With increasing time of dissociation both the cell-associated radioactivity and the radioactivity released into the incubation medium is progressively degraded. These data demonstrate that in isolated rat hepatocytes labeled insulin initially localizes to the plasma membrane, is progressively internalized, and associates preferentially with lysosomal structures. These events may provide a mechanism that links cell surface binding to the degradation of insulin and to insulin-induced loss of its specific receptor.

Animals↗
PubMed1979

Role of microtubules in the synthesis, conversion, and release of (pro)insulin. A biochemical and radioautographic study in rat islets.

In the pancreatic B cell, microtubules are thought to be involved in the process of insulin release. Their possible participation in the sequence of events leading from the biosynthesis and conversion of proinsulin to the release of newly synthesized insulin was investigated in rat isolated islets exposed to colchicine (0.1 mM). When the islets were preincubated for 30 min with colchicine and [3H]-leucine and, thereafter, incubated for two successive periods of 90 min each, still in the presence of colchicine, the release of preformed insulin was progressively inhibited and that of newly synthesized hormone delayed. When the islets were preincubated for 120 min with colchicine, subsequently pulse-labeled with [3H]leucine, and eventually examined by ultrastructural autoradiography, the export of newly synthesized proinsulin out of the rough endoplasmic reticulum, its transit through the Golgi complex, and its eventual packaging in secretory granules were all retarded. This situation was associated with a delayed conversion of proinsulin to insulin. Under the same experimental conditions, colchicine failed to affect the oxidation of glucose and adenylate charge in the islets. The effect of colchicine upon the release of preformed and newly synthesized insulin was not reproduced by lumicolchicine. It is concluded that colchicine interferes with the system controlling the intracellular transfer of secretory material from site of synthesis to site of release. This interference is likely to be linked to the effect of colchicine on microtubules.

Adenine Nucleotides↗
PubMed1979

Motile events in pancreatic endocrine cells.

Monolayer cultures of neonatal rat endocrine pancreatic cells were examined by time lapse cinematography. Motion analysis revealed two major types of motile events. On one hand, particles (0.3 micrometers in diameter) tentatively identified as secretory granules were found to undergo back and forth saltatory movements along oriented pathways. The existence of such pathways was statistically validated by the large prevalence of angles close to either 0 degrees of 180 degrees between successive movements of the same particle. The movements occurred at a mean speed of 0.8 micrometers/sec. Glucose (16.7 mM) increased the frequency of such movements. Vincristine (10 microM) caused a progressive inhibition of saltatory movements, which may depend, therefore, on the integrity of the microtubular apparatus. On the other hand, areas of the cell boundary displayed contractile-like movements, which were stimulated by insulinotropic agents, such as glucose and the ionophore A23187. Cytochalasin B also affected this second type of motile event, which is thought to reflect the activity of actin-like microfilaments. These findings suggest that the microtubular apparatus serves as a guiding cytoskeleton for the oriented translocation of secretory granules, whereas the microfilamentous cell web may control the eventual access of the granules to exocytotic sites.

Animals↗
PubMed1979

Somatostatin secretion from monolayer cultures of neonatal rat pancreas.

Monolayer cultures of neonatal rat pancreas have been characterized as an in vitro system for studying SRIF secretion. Marked 12- and 6-fold potentiation of SRIF release occurred with N-2-O-dibutyryl cAMP monosodium salt and theophylline, respectively. High glucose (300 mg/dl) stimulated SRIF release, whereas galactose was without effect. Exogenous insulin did not alter SRIF release, and the SRIF responses to theophylline and glucose were unaffected by the addition of antiinsulin serum to neutralize the insulin released by these agents. Arginine evoked a significant 2-fold increase in SRIF release. Exogenous glucagon produced slight but not significant stimulation of SRIF release. However, after exposure of the cultures to antiglucagon serum to diminish the concentration of glucagon in contact with the SRIF cells, exogenous glucagon produced a marked enhancement of SRIF secretion. These data suggest that glucose, arginine, glucagon, N-2-O-dibutyryl cAMP monosodium salt, and theophylline stimulate SRIF secretion, probably by direct effects on D cells or through mechanisms other than increased insulin secretion. Monolayer cultures of rat pancreas should provide a powerful in vitro system for studying pancreatic SRIF physiology.

Animals↗
PubMed1979

Glicentin immunoreactive cells: their relationship to glucagon-producing cells.

The cellular and subcellular localization of one of the gut glucagon-like immunoreactants (GLI-1 or glicentin) and the relative distribution of glicentin- and glucagon-containing cells were investigated by immunocytochemistry. By immunofluorescence, the antiglicentin serum, which does not react with glucagon, revealed positive cells in the islets of Langerhans and in the gut mucosa, particularly in the terminal ileum and colon. In the intestinal mucosa, it was proven ultrastructurally that the glicentin immunoreactive cells correspond to the L cell and that the secretory granules represent the storage compartment of the immunoreactive material. In pancreatic islets, consecutive semithin sections treated with antiglicentin and specific antiglucagon sera showed that the same A cell population reacted with both sera, while immunoperoxidase staining on thin sections revealed that the immunoreactive material was confined to the secretory granules. The same results were obtained on dog oxyntic mucosa, where the glicentin- and glucagon-containing cells were identified as the gastric A cell. The immunocytochemical demonstration of a common glicentin-like material in the A and L cells together with the known presence of a common immunoreactant in glicentin and glucagon strongly support the idea that the A and L cells are ontogenetically related and synthesize their secretory product via a glicentin-like precursor which, by specific cleavage, could yield glucagon and gut glucagon-like immunoreactants.

Animals↗
PubMed1979

Insulin-induced receptor loss in the cultured human lymphocyte: quantitative morphological perturbations in the cell and plasma membrane.

When cultured human lymphocytes (IM-9) are exposed to 10(-6) M procine insulin for 6 h, washed, and incubated with 125I-insulin, the ability of the cell to bind the labelled hormone is reduced by a mean of 78%. Under these experimental conditions that induce insulin-receptor loss in this cell there is a mean 95% increase in microinvaginations in the plasma membrane revealed by electron microscopy on freez-fractured replicas of the cell. At the same time, horseradish peroxidase uptake, a marker of endocytosis, is increased in the cells incubated with insulin. Coupled with our recent EM autoradiographic evidence that labelled insulin is acutely internalized by this cell, these studies are consistent with the possibility that endocytosis represents a mechanism by which receptor is removed from the cell surface.

Cell Line↗
PubMed1979

A study of glucagonomas by light and electron microscopy and immunofluorescence.

Five tumors associated with the complete glucagonoma syndrome, as well as a series of glucagon-cell adenomas from three patients without this syndrome, were investigated by light and electron microscopy and by immunofluorescence. All tumors associated with the syndrome were large, from 3 to 35 cm along the major axis, and three of them were proved to be malignant. No common histologic arrangement of tumor cells was apparent for the five neoplasms examined. Immunofluorescent staining for glucagon and glicentin was carried out: while most cells were negative, a varying number of scattered cells were positive with both antisera in all tumors except one; three tumors contained more glicentin- than glucagon-immunoreactive cells. Moreover, three tumors were multihormonal, witn cells positive for pancreatic polypeptide and/or insulin. Ultrastructurally, the secretory granules of cells from these tumors were not typical of those found in A-cells from adult human islets. The glucagon-cell tumors from patients without the syndrome were benign, usually multiple, and were small, with diameters from 0.5 mm to 1 cm. In most cases, the cells from these neoplasms arranged in a characteristic pattern (ribbonlike or "gyriform"). In most tumors, the majority of cells showed both glucagon and glicentin immunofluorescence and the ultrastructural appearance of their secretory granules was similar to that of normal islet A-cells. From the morphologic point of view, therefore, cells from tumors not associated with the glucagonoma syndrome resemble normal glucagon cells more closely than those from tumors associated with the syndrome.

Adult↗
PubMed1979

Glucagon-like polypeptides in canine brain.

Glucagon-like material has been detected by radioimmunoassay in several areas of the canine brain. High concentrations of glucagon-like immunoreactivity (GLI), measured with antibodies directed against the N-terminal region of glucagon, have been found in the hypothalamus, amygdala, and mesencephalon, but a high concentration of immunoreactive glucagon (IRG), measured with antibodies directed against the C-terminal region of glucagon, has been found only in the hypothalamus. The predominant molecular forms of GLI isolated from brain extracts by affinity chromatography are the same as those isolated from gut extracts. The predominant form of IRG in brain extracts is of the same (approximate) molecular weight as pancreatic glucagon.

Animals↗