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Biomedical subjects

L Luciano

Publications and source records attributed to L Luciano.

At least 73 records · Page 4Linked to original sources
PubMed1989

Localization of cholesterol in the colonic epithelium of the guinea pig: regional differences and functional implications.

It is generally accepted that variations in membrane cholesterol content affect the fluidity of the bilayer, thus altering its permeability. In the biological membranes, in physiological conditions, a high cholesterol content rigidifies the bilayer decreasing its permeability, a lower cholesterol content induces the opposite effect by increasing the permeability. Since differences in the epithelial permeability for short chain fatty acids have previously been demonstrated in the proximal and distal colon of the guinea pig, these two regions were investigated to establish whether differences in membrane cholesterol content of the absorbing cells can be demonstrated. Freeze-fracture replicas of filipin-treated colonic tissue were used. The results show that in the proximal colon the density of filipin cholesterol complexes located on the luminal plasma membrane of the columnar absorbing cells was significantly higher (about twice) than in the distal colon. Therefore the lower amount of cholesterol present in the membrane of the absorbing cells in the distal colon indicates a greater fluidity of the membranes of the epithelial cells in this region. Such fluidity could be correlated to the higher absorption rates of shortchain fatty acids characteristic of this region.

Animals↗
PubMed1989

Retinal wound healing after surgical contusion injury.

The lesion was caused by a compression injury to the retina with a vitrectomy instrument in a rhesus monkey; the lesion was examined by electron microscopy 8 years later. The inner surface of the choroid was lined by a layer of cells with the characteristics of fibroblasts. The choriocapillaris was missing. Bruch's membrane was extremely thickened and showed numerous changes. In the center of the scar, the retinal pigment epithelium was discontinuous. The neuroretinal portion of the scar was composed of distorted and dislocated nerve cells, nerve fibers, and glial elements that were probably Müller cells. Towards the vitreous cavity, the surface of the scar contained numerous microvillous processes. A band of zonulae adherentes resembling the outer limiting membrane was seen immediately adjacent to the surface. No inner limiting membrane was seen in the entire scar area.

Animals↗
PubMed1989

Alignment of cholesterol in the membrane bilayer.

Freeze-fracture replicas of filipin-treated samples of guinea pig colon mucosa reveal areas in the membrane of the goblet cell granules labeled by filipin-cholesterol complexes (FCC) intermingled with regions patterned by "lines." The FCC and "lines" are arranged in an approximately rhombic pattern. Other membranes of the same cell or of other cells display either FCC only, aligned and occasionally ordered in "rhombs," "lines" only, with a similar pattern, or randomly distributed FCC. Optical diffraction was used to analyze and compare replicas of membranes with ordered FCC and "lines", as well as randomly distributed FCC. The results demonstrate that all these structures are reciprocally related through a common distribution pattern in the membrane. This observation supports the assumption that cholesterol has a preferential ordered distribution within the membrane bilayer.

Animals↗
PubMed1987

Interaction of polymyxin B nonapeptide with anionic phospholipids.

The interaction of polymyxin B nonapeptide (PMBN) and polymyxin B (PMB) with the anionic phospholipids phosphatidylserine (PS), dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidic acid (DPPA), and 1:1 mixtures (w/w) of DPPA and distearoylphosphatidylcholine (DSPC) was studied by calorimetry, electron spin resonance, and fluorescence spectrometry, electron microscopy, and fusion and leakage assays. The phase transition temperatures of DPPA and DPPG were very similar when bound to PMB or PMBN, indicating that the lipids are in a similar state when bound to the cationic peptides. Both PMB and PMBN caused the interdigitation of DPPG bilayers, suggesting that the penetration of hydrophobic side chains from a peptide bound electrostatically on the surface is sufficient to induce this phenomenon. Stopped-flow experiments revealed that PMBN and PMB induced the fusion of small unilamellar PS and large unilamellar DPPA-DSPC vesicles. The aggregation of vesicles was found to be diffusion-controlled process; the subsequent fusion took place with a frequency of 10(2)-(5 X 10(2] s-1 for small vesicles and 1-100 s-1 for large vesicles. The freeze-fracture replicas of the PMB-treated vesicles displayed 12-50-nm depressions on several superimposed bilayers, indicating the formation of stable lipid-PMB domains. Since the incubation with PMBN produced similar depressions only if the specimens were fixed, PMBN-induced domain formation seems to be a reversible rapid process. The differences in the phospholipid-peptide interactions are correlated with the differences in the physiological action of the antibiotic PMB and the nonbactericidal PMBN on the cell envelope of Gram-negative bacteria.

Calorimetry, Differential Scanning↗
PubMed1986

Histochemical demonstration of hyaluronic acid molecules by alcian blue.

Specimens of vitreous humour (monkey eye), Wharton jelly (human umbilical cord) and commercial hyaluronates were immersed in buffered fixative solutions containing either aldehydes and Alcian Blue, or aldehydes and Alcian Blue with MgCl2 as electrolyte. Two MgCl2 concentrations were used, 0.025 M and 0.3 M. Immersion in both solutions induced formation of precipitates which were postfixed in OsO4, dehydrated and embedded for thin section electron microscopy. The use of the same fixative solution produced morphologically comparable precipitates from all three materials. The precipitates, especially after fixation in the presence of electrolyte, were composed of linear, unbranched filaments, frequently aggregated into bundles. The filaments were considered to be molecules of hyaluronic acid.

Alcian Blue↗
PubMed1985

Cationic dyes reveal proteoglycans on the surface of epithelial and endothelial kidney cells.

The glomerular epithelial cells of the rat kidney fixed by vascular perfusion with an aldehyde solution containing either safranine O or alcian blue (and 0.3 M MgCl2) display filaments which are located close to the outer surface of the plasma membrane. These filaments are similar to those revealed by the same methods in the laminae rarae of the glomerular basement membrane. Alcian blue (and MgCl2) further demonstrates the presence of anionic sites inside the endothelial cell pores of the glomerular and peritubular capillaries, on the luminal surface of endothelial cells of large renal vessels and along the basolateral surface of the epithelial cells of the Bowman capsule and of the proximal convoluted tubule.

Alcian Blue↗
PubMed1985

Filipin-cholesterol complexes (FCC) in the goblet cell granule membrane of the distal colon are arranged in a rhombic pattern.

After fixation in the presence of filipin, the membrane of the goblet cell granules of the distal colonic mucosa (guinea pig) displays, in freeze-fracture replicas, a rhombic pattern composed of intersecting "lines" of unknown nature. The filipin-cholesterol complexes of the granule membrane are ordered according to the same geometry. This arrangement--but not the "lines"--has been found for the filipin-cholesterol complexes of other membranes of the same goblet cells as well as of other colonic cells. These observations indicate that in some biological membranes cholesterol has an ordered distribution, comparable to that suggested by investigations on artificial membranes.

Animals↗
PubMed1984

Structure of zonulae occludentes and the permeability of the epithelium to short-chain fatty acids in the proximal and the distal colon of guinea pig.

Absorption of short-chain fatty acids has been studied in the proximal and the distal colon of anaesthetized guinea pigs. Segments were perfused with a solution similar in chemical composition to that of normal colonic fluids. In the proximal colon the permeability of the mucosa was similar for acetate, propionate and butyrate. For acetate the permeability was significantly higher in the proximal than in the distal colon, and the reverse was seen for butyrate. In the distal colon the short-chain fatty acids seem to be absorbed mainly in the undissociated form due to their lipid solubility; a paracellular pathway for the dissociated molecules is of no major importance. In the proximal colon, on the other hand, a considerable portion of acetate and propionate disappears in the ionized form. Light microscopy (semithin sections) and electron microscopy (freeze-fracture replicas) showed remarkable morphological differences between the proximal and the distal colon. "Leaky spots" with only few strands were present in the zonulae occludentes between the epithelial cells at the surface of the proximal colon. In the distal colon the junctions between the cells were more compact, and significantly more strands separated the lumen from the intercellular space. These results suggest that short-chain fatty acids could be absorbed by a paracellular pathway in the proximal colon, and not in the distal colon. In the proximal colon the number of strands of the zonulae occludentes between surface cells and that between cryptal cells was similar. On the contrary, in the distal colon significantly more strands were present between surface cells than between cryptal cells. Morphological and physiological considerations suggest that absorption of short-chain fatty acids in the crypts is negligible.

Animals↗
PubMed1983

Ultrastructural architecture of proteoglycans in the glomerular basement membrane. A cytochemical approach.

Rat kidneys were perfused with fixative solutions containing either a) a polycationic dye (Alcian blue 8 GX, Astra blue 6 GLL, cuprolinic blue, ruthenium red), b) a monocationic dye (safranine 0), or c) Alcian blue in the presence of a 0.3 M MgCl2 concentration. Whereas solutions of a revealed the glomerular basement membrane proteoglycans as particles or threads 60 nm apart and arranged in a reticular pattern, solutions of b and c demonstrated new morphological aspects of these molecules. They appeared as tiny filamentous structures, about 100 to 160 nm long, ordered in a network-like pattern with a mesh of about 60-nm width. The filaments displayed lateral branches about 20 nm apart and about 25 nm long, projecting within the meshes. We suggest that the filamentous structures are the protein core, and the branches are the glycosaminoglycans of proteoglycan molecules. Because of this arrangement the negatively charged sites of the glomerular basement membrane would lie closer to each other than previously assumed.

Animals↗
PubMed1981

The brush cells of the common bile duct of the rat. This section, freeze-fracture and scanning electron microscopy.

Two different fixative procedures (immersion and perfusion) and four different fixative solutions were used in order to obtain the best preservation of the brush cells of the common bile duct of the rat. The results indicate that only perfusion fixation through the common bile duct is suitable, independent of the fixative solutions and their osmolarity. Numerous brush cells were seen in the proximal and distal regions of the common bile duct. In these locations, they could be implicated in a registration and/or regulation of intraluminal pressure variations.

Animals↗
PubMed1981

Occluding junctions surrounding cystoid spaces in the human peripheral retina. A thin-section and freeze-fracture study.

Transmission electron microscopic examination of thin sections and freeze-fracture replicas of areas neighboring cystoid spaces in the peripheral human retina reveals extensive networks of occluding junctions on all sides of these spaces. These junctions may be responsible for the fact that, in spite of the absence of an epithelial lining, fluid from the spaces of cystoid degeneration and retinoschisis does not leak into the surrounding retina, which would lead to their collapse.

Extracellular Space↗
PubMed1981

Glomerular basement membrane and mesangial matrix: a comparative study in different vertebrates.

Perfusion fixation of the rat kidneys with aldehydes and alcian blue demonstrates within the glomerular mesangium various components displaying anionic binding sites. These are the surface coat of the mesangial cells, numerous mesangial microfibrils (probably glycoproteins), and polygonal particles (Presumably proteoglycans). These particles lie close to the mesangial cells and form assemblies of various extension within the mesangial matrix as well. In addition, a discontinuous basement membrane can be recognized which surrounds the mesangial cells. In the hagfish glomeruli (fixed without cationic dye), a prominent layer of microfibrils is interposed between mesangial and endothelial cells. Both these cells show incomplete basement membranes.

Animals↗
PubMed1980

The fine structure of the stomach mucosa of the Llama (Llama guanacoe). II. The fundic region of the hind stomach.

The epithelium of the fundic region mucosa of the hind stomach in the Llama guanacoe has been studied using morphological and histochemical methods. Morphology suggests that solute and water absorption may occur in the epithelium of the surface and of the foveolae, although this absorption can not be estimated because of the extensive secretion of the gastric glands. The same cells of the surface and foveolar epithelium show numerous secretory granules. The glands reveal neck cells, chief cells, a large number of oxyntic cells, four types of endocrine cells (A-like, ECL, D and EC), brush cells and wandering cells. PAS and Alcian blue reactions for light microscopy suggest a secretion of neutral and acidic mucosubstances in the surface and foveolar epithelium, of neutral mucosubstances only in the neck cells. Periodic acid-thiocarbohydrazide silver proteinate (PA-TCH-SP) reaction for electron microscopy confirms the presence of neutral mucosubstances within the secretory granules of the surface, foveolar and neck epithelial cells. In all these cells, the reaction product is also evident within sacculi and vesicles of the maturing surface of the Golgi apparatus. A positive PA-TCH-SP reaction also occurs on the membrane (and not on the contents) of the Golgi apparatus (maturing surface) and of the secretory granules of the chief cells as well as on the membrane of the Golgi apparatus and of apical vesicles and tubules of the oxyntic cells. In addition, silver granules slightly enhance the electron desity of the contents of the secretory granules in the endocrine cells. Morphological and histochemical findings are discussed and compared with results described by others for monogastric mammals.

Aminosalicylic Acid↗
PubMed1980

Cell junctions of the glomerular epithelium in a very early vertebrate (Myxine glutinosa).

The glomerular epithelial cells of the Atlantic hagfish (Myxine glutinosa) lack a slit diaphragm which is replaced by filaments. The epithelial cells show numerous occluding junctions (maculae and fasciae occludentes), septate desmosome-like junctions and desmosomes. The present findings are compared with available data on developing and mature glomerular epithelial cells of mammals.

Animals↗