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Biomedical subjects

L Orci

Publications and source records attributed to L Orci.

551 records · Page 31Linked to original sources
PubMedDate not supplied

Insulin receptor internalization and recycling: mechanism and significance.

Using a 125I-photoreactive insulin analogue that can be covalently coupled to its receptor we have shown that in rat hepatocytes the insulin receptor is concomitantly internalized with the labeled hormone and afterwards is progressively recycled back to the cell surface. In the course of the internalization process the insulin-receptor complex associates with clear vesicles and later on with lysosomes from which it is recycled through clear vesicles. On the basis of these observations it is suggested that modulation of the rates of internalization and of recycling of the insulin receptor can regulate the number of available surface insulin receptors. This hypothesis is supported by the results of experiments showing that monensin, an inhibitor of receptor recycling enhances insulin induced loss of its own surface receptors (down regulation) in U-937 monocytes.

Affinity Labels↗
PubMedDate not supplied

Vasopressin stimulates formation of coated pits in rat kidney collecting ducts.

The water permeability of collecting ducts is greatly increased by the antidiuretic hormone, vasopressin. This permeability increase is associated with the appearance of intramembrane particle (IMP) clusters on the luminal plasma membranes of principal cells of the collecting duct epithelium. IMP aggregates have also been related to an increase in water permeability of two other vasopressin-sensitive epithelia, the amphibian urinary bladder and the amphibian epidermis, and it has been proposed that these specialized membrane domains might represent specific water-permeable membrane patches, induced by the hormone in their respective epithelia. Using a cytochemical probe for membrane cholesterol, filipin, we show here that the membrane patches in rat kidney are selectively devoid of filipin-sterol complexes and that when identified in thin sections, they have a cytoplasmic bristle coat: both of these features are characteristics of coated pits which, in other systems, are involved in receptor-mediated endocytosis. We also show that vasopressin induces the appearance of coated pits on collecting duct luminal membranes in Brattleboro homozygous rats, which have hereditary diabetes insipidus.

Animals↗
PubMedDate not supplied

Evidence for polarization of plasma membrane domains in pancreatic endocrine cells.

Polarization of plasma membrane domains is an essential feature of secretory epithelial cells from exocrine glands. The surface of exocrine cells (a typical example is the acinar cell of the pancreas) is separated into an apical domain, where secretion occurs by exocytosis, and a basolateral domain, which senses variations of the internal milieu and is enriched with receptors for various hormones and secretagogues. It is unknown whether secretion is polarized in endocrine cells (except for thyroid follicular cells, which are organized into cavitary structures). To determine whether distinct plasma membrane domains exist in endocrine cells, we infected monolayer cultures of pancreatic endocrine cells with enveloped RNA viruses known to bud selectively from either the apical or basolateral domain in polarized epithelial cells. This asymmetrical budding is thought to reflect the polarized nature of the infected cells, as in non-polarized cells such as fibroblasts, the same viruses bud nonselectively from the entire cell surface. We show here that influenza virus and vesicular stomatitis virus (VSV) emerge asymmetrically from cultured pancreatic islet cells; this represents the first evidence for polarization of plasma membrane domains in pancreatic endocrine cells.

Animals↗
PubMedDate not supplied

The condensing vacuole of exocrine cells is more acidic than the mature secretory vesicle.

A number of intracellular, membrane-bound compartments in both the endocytic and exocytic pathways of eukaryotic cells have an acidic internal pH. In endocrine cells, the mature secretory vesicle has an acidic pH; secretory vesicles isolated from exocrine cells, however, appear to have a neutral pH. Recently we have used a newly developed immunocytochemical technique to map low-pH compartments in insulin-secreting islet cells with the electron microscope and find that during the maturation of the secretory vesicle there is a progressive acidification of these vesicles that begins as soon as the trans Golgi condensing vacuoles form. Now we have used this technique to examine two exocrine cells: the pancreatic acinar cell and the parotid serous cell. In both cell types, the trans Golgi condensing vacuoles are acidic and accumulate the low-pH probe to the same extent as condensing vacuoles of insulin-secreting islet cells. Unlike insulin-secreting cells, however, maturation of the granules is accompanied by a return of luminal pH to near neutrality. Therefore, although the pH of storage granules in exocrine and endocrine cells is different, the pH of the condensing vacuoles in both cells is acidic.

Amylases↗
PubMedDate not supplied

Internalization of 125I-insulin by IM-9 cultured human lymphocytes: a comparison between A14-monoiodo-pork and biosynthetic human insulin.

Human insulin synthesized from A- and B-chains separately produced in Escherichia coli from cloned genes was characterized by examining its interaction biochemically and morphologically with IM-9 cultured human lymphocytes. Biosynthetic human insulin (BHI) behaves similarly to pork insulin with respect both to its binding properties and to the rate and magnitude at which it is internalized by the cells.

Animals↗
PubMedDate not supplied

Neonatal islet cell adenoma: a distinct type of islet cell tumor?

An encapsulated, compact-type islet cell adenoma of the pancreas, found in a newborn infant with hyperinsulinemic hypoglycemia, was investigated by conventional histology and immunofluorescence. Although the histologic structure of the tumor was indistinguishable from that of most islet cell tumors of adults, immunofluorescence revealed that the four islet cell hormones (insulin, glucagon, somatostatin, and pancreatic polypeptide) were all present in the tumor. They were stored in different cells that showed the same spatial distribution usually seen in normal islets. We conclude that neonatal islet cell adenoma can be distinguished from those of adults on the basis of the content and topographic distribution of their constituent endocrine cells.

Adenoma, Islet Cell↗
PubMedDate not supplied

Receptor-linked degradation of 125I-insulin is mediated by internalization in isolated rat hepatocytes.

When hepatocytes were freshly isolated from rat liver and incubated for various periods of time at 37 degrees C, the media from the incubation, when completely separated from the cells, actively degraded 125I-insulin. THis soluble protease activity was strongly inhibited by bacitracin but was unaffected by the lysosomatropic agent ammonium chloride (NH4Cl). When hepatocytes were incubated with 125I-insulin at 37 degrees C in the presence or absence of 8 mM NH4Cl the ligand initially bound to the plasma membrane and was subsequently internalized as a function of time. When hepatocytes were incubated at 37 degrees C for 30 minutes with 125I-insulin in the presence of bacitracin and NH4Cl or bacitracin alone and the cells were washed, diluted, and the cell-bound radioactivity allowed to dissociate, the percent intact 125I-insulin in the cell pellet and in the incubation media was greater in the presence of NH4Cl at each time point of incubation. Under these same conditions a higher proportion of the cell-associated radioactivity was internalized and a higher proportion was associated with lysosomes. The data suggest that receptor-mediated internalization is required for insulin degradation by the cell, and that this process, at least in part, involves lysosomal enzymes. Furthermore, the data demonstrate that internalization is not blocked by the presence of bacitracin or NH4Cl in the incubation media, but that degradation is inhibited.

Ammonium Chloride↗