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Biomedical subjects

R Montesano

Publications and source records attributed to R Montesano.

At least 235 records · Page 13Linked to original sources
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

Membrane particle arrays in SV40-transformed 3T3 cells.

The ultrastructural organization of the plasma membrane of untransformed and simian virus (SV)40-transformed 3T3 cells in culture was studied by an in situ freeze-fracturing technique. Both 3T3 and SV3T3 cells showed randomly distributed intramembrane particles as well as gap junctions. In addition, the plasma membrane (P-face) of confluent SV40-transformed 3T3 cells was found to display a unique membrane specialization which was not observed in normal 3T3 cells. This membrane specialization consisted of irregularly-shaped arrays of loosely dispersed large (11-12 nm) intramembrane particles, located in regions of close contact between adjacent SV3T3 cells. When a P- to E-fracture face transition occurred within the boundaries of a particle array, the intracellular space appeared uniformly reduced and arrays of pits coextensive with the P-face particles could be recognized on the E-face. Particle arrays appeared particularly prominent in SV3T3 cells grown in the presence of high serum concentrations (20% foetal calf serum or calf serum). Particle arrays resembling those found in SV3T3 cells were observed only in very rare instances in the plasma membrane of other virus-transformed cell lines. Several possible interpretations of the meaning of the particle arrays, including the hypothesis thay they represent an unusual or abortive form of intracellular junction, are discussed. The absence of similar membrane specializations in the plasma membrane of untransformed 3T3 cells points to a difference in membrane organization and cell contact ultrastructure between normal and SV40-transformed 3T3 cells.

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

Plasma cell endocytosis: is it related to immunoglobulin secretion?

Mouse plasma cells have been exposed to a wide range of soluble and adsorptive macromolecular tracers for 10 min to 4 h to explore the possibility of membrane recycling related to the high secretory rate of these nonregulated secretory cells. Electron microscopic examination showed in all cases labeling of multivesicular and multilamellar bodies and a lesser labeling of smooth-surfaced vesicles. Using cationized ferritin as tracer, an additional very restricted labeling of Golgi cisternae was observed. Comparable labeling patterns were observed when immunoglobulin (Ig) secretion was blocked with the Golgi-specific pertrurbant, monensin, and in the case of poorly differentiated B immunoblasts which secrete little or no Ig. Our observations therefore emphasize that available approaches cannot yet determine whether a mandatory circuit of vesicular traffic couples Ig exocytosis to endocytosis.

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

Intramembrane events accompanying junction formation in a liver cell line.

To study intramembrane events leading to the establishment of intercellular junctions between epithelial cells in vitro, we examined monolayer cultures of a rat liver cell line by an in situ freeze-fracturing technique (Pauli et al., J. Cell Biol., 72:763, 1977). Our observations indicate that an early step of junction formation between liver cells consists of the differentiation of a particle-poor membrane stretch showing a honeycomb pattern of shallow P-face depressions or E-face bulges ("formation band"). This change in membrane organization precedes and accompanies the subsequent aggregation of junctional particles. The latter process results in the formation of irregular particle islands with peripheral branchings which tend to encompass the depressions in the membrane. The linear branchings grow and interconnect in a network of beaded strands, which gradually transform into smooth tight junctional fibrils, as previously described in fetal liver in vivo (Montesano et al., J. Cell Biol., 67:310, 1975), while the particle islands assume the typical configuration of mature gap junctions. Formation bands are particularly prominent between liver cells growth in the presence of hydrocortisone (5 microgram/ml) in the culture medium.

Animals↗
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

Surface proteins in normal and transformed rat liver epithelial cells in culture.

The pattern of surface proteins of different types of normal and transformed rat liver cells have been studied in culture by means of lactoperoxidase-catalysed iodination procedures, followed by SDS-gel electrophoresis. The cells examined were primary cultures of epithelial liver cells, long-term cultures of epithelial liver cells, in vitro transformed epithelial liver cell lines and liver tumour-cell lines; mesenchymal cells from liver and skin were also examined. The principal surface proteins of primary cultures of epithelial cells from adult or neonatal rats had components with mol. wts of 140,000-160,000, 100,000 and 40,000-70,000. A band that had the same position as fibronectin from mesenchymal cells was also present and this band, as well as other iodinated components, were less sensitive to trypsin than fibroblastic fibronectin. A similar pattern of iodinated proteins was seen in long-term cultures of epithelial liver cells, with a great reduction in the number and intensity of the bands in the mol. wt region below 100,000. Almost all the in vitro transformed and tumour epithelial cell lines contain a protein with a mol. wt 135,000 as one of the major iodinated bands, and in contrast to the observation in transformed fibroblasts, the fibronectin was retained by most of these transformed cell lines.

Animals↗
PubMed1980

Membrane specialization in the rat epididymis. I. Rod-shaped intramembrane particles in the apical (mitochondria-rich) cell.

Following freeze-fracture of the rat epididymis, a population of cells whose apical, but not baso-lateral, plasma membrane contains elongated intramembrane particles was found in the initial segment. From their size, shape and distribution, these cells are assumed to be the so-called apical cells of this segment. Apical cells also contain the enzyme, carbonic anhydrase which, together with the presence of rod-shaped particle on their membranes, permits their classification as 'mitochondria-rich' cells, a specialized cell type found in some transporting epithelia. On the basis of these observations, we suggest that the apical cells may play a role in fluid and/or electrolyte transport in the initial segment of the epididymis.

Animals↗