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Biomedical subjects

A Perrelet

Publications and source records attributed to A Perrelet.

At least 91 records · Page 5Linked to original sources
PubMed1978

Freeze-fracture of membrane fusions in phagocytosing polymorphonuclear leukocytes.

Freeze-fracture of rabbit polymorphonuclear leukocytes in the process of phagocytosing yeast cells shows changes in storage granule and phagosome membranes essentially similar to those described in mammalian secretroy cells during exocytosis. These changes consist of the clearing of intramembrane particle from limited zones of the fusing granule and phagosome membranes. After the completion of fusion, which leads to the incorporation of storage granule membrane into the phagosome membrane, particle-free patches are no longer visible, but the phagosome membrane contains some loose aggregates of particles. These data suggest that intracellular membrane fusion in polymorphonuclear leukocytes occurs through interaction of protein-depleted areas of the involved membranes.

Animals↗
PubMed1977

Morphological changes of the adipose cell plasma membrane during lipolysis.

Morphological changes of the plasma membrane in the white adipose cell associated with lipid mobilization were assessed qualitatively and quantitatively on freeze-fracture replicas of epididymal adipose tissue from fasted and from streptozotocin-diabetic rats. The number of plasma membrane invaginations and intramembranous particles were evaluated per square micrometer of membrane and per entire adipocyte. These two determinations show that the number per square micrometer (local concentration) of both structural features progressively increases with the duration of diabetes and fasting, while that at the same time their number per entire cell (total content) remains unchanged. These data thus show: (a) a reorganization of the adipose cell plasma membrane during lipolysis; and (b) that this reorganization can be detected only by determining the concentration and the total content of the structural features of the membrane involved.

Adipose Tissue↗
PubMed1977

Membrane particle changes attending the acrosome reaction in guinea pig spermatozoa.

To examine the freeze-fracture appearance of membrane alterations accompanying the preparation of sperm membranes for fusions-the first preparatory stage occurring before physiological release of the acrosomal content, the second afterward-we induced the acrosome reaction in capacitated guinea pig spermatozoa by adding calcium to the mixture. The most common features observed before fusion of the acrosomal and plasma membranes were the deletion of fibrillar intramembranous particles from the E-fracture faces of both membranes, and the clearance of globular particles from the P face of the plasma membrane-events taking place near the terminus of the equatorial segment. Large particles, >12nm, remained not far from the cleared E-face patches. The P face of the outer acrosomal membrane is virtually clear from the outset. In addition, when fusion was completed, occasional double lines of large particles transiently embossed the P face of the plasma membrane (postacrosomal) side of the fusion zone. Behind the line of fusion, another series of particle-cleared foci emerged. We interpreted these postfusion membrane clearances as a second adaptation for sperm-egg interaction. Induction of the acrosome reaction in media containing phosphatidylcholine liposomes resulted in their apparent attachment, incorporation, or exchange in both the originally and secondarily cleared regions. Our observations support the concepts that membranes become receptive to union at particle- deficient interfaces, and that the physiologically created barren areas in freeze-fracture replicas may herald incipient membrane fusion.

Acrosome↗
PubMed1977

Freeze-fracture of membrane fusions during exocytosis in pancreatic B-cells.

To examine the freeze-fracture appearance of membrane alterations at sites of exocytosis in mammalian cells, we studied the secretory granule and plasma membrane of rat pancreatic B-cells during glucose-stimulated insulin secretion. Constant features observed were the scarcity of particles in secretory-granule P-fracture faces and the almost total clearance of intramembranous particles in P-and E fracture faces of the plasma membrane in areas of close apposition of these two membranes preceding fusion; also observed was the temporary persistence of particle-cleared regions after the fusion was completed. Our observations thus support the concept that membranes fuse at sites of closely apposed, particle-free regions and that the physiologically created clear areas found in freeze-fracture replicas of the plasma membrane are the hallmarks of incipient or recent membrane fusion.

Animals↗
PubMed1977

The effects of anoxia on the morphology and composite metabolism of the intact aortic intima-media preparation.

Paired samples of an intact rabbit aortic intima-media preparation were incubated for short periods under aerobic or anoxic conditions in Krebsbicarbonate buffer containing 6% albumin and 5 mM glucose. During aerobic incubation for as long as 1 h the preparation retained an electron microscopic (EM) appearance similar to that of tissue fixed in situ, and scanning EM confirmed the presence of an uninterrupted endothelial surface. After 2.5 min of anoxia there was widespread endothelial swelling, but the alterations in the EM appearance of these cells were not striking and did not progress during a subsequent 30 min aerobic incubation in fresh medium. After 10 min of anoxia there were marked and widespread alterations in endothelial cell structure, including loss of cell integrity, and numerous discrete interruptions in the endothelium were consistently observed on both transmission and scanning EM. After a subsequent 30 min aerobic incubation in fresh buffer, a major fraction of the luminal surface was denuded of endothelium. The aortic vascular smooth muscle cells did not exhibit evidence of irreversible anoxic injury after 2.5 or 10 min of anoxia or after subsequent aerobic incubation for 30 min. Exposure to anoxia for 10 min induced persistent alterations in the composite metabolism of the preparation during subsequent aerobic incubation in fresh medium; O(2) uptake was reduced, and the fraction of the glucose uptake that was accounted for by lactate production increased approximately 100%. The observations suggest that aortic endothelial cells are dependent upon respiration for the preservation of normal ultrastructure and cell integrity, and probably derive the major fraction of their energy requirements from reactions linked to respiration. Under the conditions employed in these experiments, short periods of anoxia did not induce EM evidence of irreversible anoxic injury in aortic vascular smooth muscle cells; this negative result is not incompatible with other data suggesting that these cells normally derive the major fraction of their energy requirements from respiration. Aortic intima-media does not exhibit a high rate of aerobic glycolysis under aerobic conditions which preserve a normal EM appearance of the preparation, but this pattern of metabolism can be induced by prior anoxic exposure.

Aerobiosis↗
PubMed1977

Pore-like structures in biological membranes.

In freeze-fracture replicas, biological membranes appear as smooth surfaces interrupted by random globular protrusion, the intramembrane particles. Smooth areas correspond to the membrane phospholipidic domain, while intramembrane particles are the morphological counterpart of membrane proteins. In the present work, examination of membranes in a variety of cell types reveals that a number of intramembrane particles contain an electron-dense spot. The spot is thought to correspond to a minute pit in the particle, filled by the platinum used in the freeze-fracture procedure. Similar images, described previously in intramembrane particles forming the specific array of the gap junction, were interpreted as hydrophilic channels bridging the interior and the exterior of the plasma membrane. Comparison between the gap junction particles and the non-junction particles containing a dense spot suggests that these latter may too contain hydrophilic channels. The channels in random intramembrane particles would represent the morphological counterparts of the water-filled pores described in models of membrane permeability.

Animals↗
PubMed1977

Perturbation of the adipose cell plasma membrane in obese (ob/ob) mice.

The plasma membrane organization of adipocytes of genetically obese (ob/ob) mice has been studied by freeze-fracture and compared to that of control (lean) mice and of small and large adipocytes in rats of different age. The large size increase of ob/ob adipocytes is accompanied by a decrease in the concentration of surface invaginations and of intramembrane particles in the plasma membrane as compareed to control, nonobese mice. By contrast, the membrane of large adipocytes of normal old rats has a concentration of invaginations and particles similar to that present in the membrane of small adipocytes of young rats. Thus, the changes of the plasma membrane organization in ob/ob adipocytes seems not to be due to size increase only but may reflect a more general perturbation of the membrane, such as evidenced by the reduced insulin and lectin binding capacity demonstrated in these cells.

Adipose Tissue↗
PubMed1976

[Ultrastructural changes in the organization of plasma membranes in adipocytes of obese mice (ob/ob)].

Freeze-fracture replicas were obtained from adipocytes in control and obese (ob/ob) Mice. Quantitative evaluation of the replicas shows that plasma membranes of adipocytes in ob/ob Mice have 50% less intramembrane particles than plasma membranes in control Mice. Since intra-membrane particles represent, at least in part, the proteins of the membrane, this suggests a decreased protein concentration, as well as a perturbed protein-lipid ratio in adipocyte membranes of obese Mice.

Adipose Tissue↗
PubMed1976

In vivo induction of tight junction proliferation in rat liver.

The chronic administration of phalloidin induces an extensive development of tight junctions between rat hepatocytes. The junctional strands lose their predominantly parallel orientation with respect to the canalicular lumen and extend abluminally in irregular patterns which cover large membrane areas at considerable distance from the bile canaliculi. These changes indicate both proliferation and provide further evidence that these junctions are not permanent differentiations of the cell membrane.

Animals↗
PubMed1976

Morphological changes in tight junctions of Necturus maculosus proximal tubules undergoing saline diuresis.

Tight junctions between epithelial cells are believed to control the paracellular diffusion of substances across epithelia. Epithelia in which tight junctions are poorly developed display a higher paracellular electrical conductance, while those with extensive tight junctions show lower conductance values. We described here a particular epithelium, that of the proximal tubules of the Necturus kidney, in which the development of the tight junctions varies in parallel with a change of paracellular electrical conductance. In control conditions, tight junctions between epithelial cells of the proximal tubules are more developed than in tubules undergoing saline diuresis, a situation which increases the conductance across the paracellular shunt pathway.

Animals↗
PubMed1976

Patterns of calcium localization in pancreatic endocrine cells.

Subcellular calcium localization in the dndocrine cells of rat pancreas was studied by the pyroantimonate precipitation technique. Calcium-containing electron-dense deposits in the endocrine cells were mostly found within secretory granules and along the plasma membrane, but their pattern of distribution in A-, B- and D-cells displayed qualitative and quantitative differences. In B-cells, numerous secretory granules contained deposits located in the halo surrounding the granule core. In A-cells, only few granules contained precipitates in their halo, whereas in D-cells, deposits were situated in the dense core of the secretory granules. Deposits along the plasma membrane occurred generally on the outer leaflet of the plasma membrane of B- and D-cells and on the inner leaflet of that of A-cells. In islets incubated at a high glucose concentration or in the presence of the calcium ionophore A23187, the number of beta granules containing precipitates was significantly increased. By contrast, only few deposits were observed in B-cells incubated in calcium-deprived medium enriched with EGTA. These findings indicate that: the pattern of calcium localization varies in different islet cell types; in B-cells the secretory granules represent one of the major stores of intracellular calcium; and that this store undergoes changes in conditions which alter insulin release.

Animals↗