PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Freezing”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed1997

Ultrastructural immunolocalization of polyamines in HeLa cells subjected to fast-freezing fixation and freeze substitution.

Polyamines have been localized at the ultrastructural level in HeLa cells subjected first to fast-freezing fixation (FFF)-freeze substitution (FS) and then to an immunocytochemical method combining anti-polyamine antibodies and immunogold labelling. Polyamines were found in both the cytoplasm and the nucleus and, in the latter, particularly over the dense chromatin area. To our knowledge, this is the first example of the electron microscopic localization of a hapten after FFF-FS. For the preservation of fine ultrastructural details, this FFF-FS method is not only adequate but also greatly reduces, if not totally eliminates, any leeching-out and redistribution of the polyamines during the preparation of the sample. For the preservation of antigenicity in situ during FS, epoxy resin was more effective than hydrophilic LR white resin, probably due to the solubility of polyamines in the latter.

Acetone↗
PubMed1985

Preservation of integrity of the inner mitochondrial membrane after freeze-thawing and freeze-drying.

The results of this paper illustrate that trehalose partially preserves inner mitochondrial membrane integrity after freeze-thawing and freeze-drying with subsequent rehydration in water. The 2,4-dinitrophenol stimulation of ATPase activity was used as a criterion for membrane integrity. The results show that ATPase activity of lyophilized-rehydrated mitochondria was stimulated up to two to three times.

Animals↗
PubMed2005

Spray freezing into liquid versus spray-freeze drying: influence of atomization on protein aggregation and biological activity.

Protein aggregation and enzyme activity were compared for reconstituted lysozyme particles produced by two cryogenic technologies, spray freezing into liquid (SFL) and spray-freeze drying (SFD). The particles were characterized by enzyme activity measurements, scanning electron microscopy (SEM), light scattering, X-ray photoelectron spectroscopy (XPS) and BET specific surface area analysis. Highly porous microparticle aggregates of protein nanoparticles, observed by SEM, were produced by both processes. The smaller degree of protein aggregation and smaller losses in enzyme activity for the SFL process relative to the SFD process were due primarily to the spraying step. The higher stability of the SFL versus SFD powders was consistent with the smaller surface excess of lysozyme measured by XPS in SFL, resulting from the reduced time of exposure to the air-water interface during atomization. For pure lysozyme, the degree of aggregation and enzyme activity were comparable for lyophilization and SFL, despite the much larger particle surface area for SFL.

Enzyme Stability↗
PubMed1999

What happens in freezing bodies? Experimental study of histological tissue change caused by freezing injuries.

In order to evaluate histological features of freezing damages to human tissue after death, we froze samples of liver and heart tissue to temperatures of -12 degrees C, -28 degrees C and -80 degrees C, and stored them for 24 and 72 h, respectively, at those temperatures. After thawing and routine preparation for histology, the samples were evaluated both by microscope and with an electronic image analyzer. In all cases, we found extended extracellular spaces and shrunken cells resulting from the freeze-thaw cycle. These features were more pronounced in tissues stored for longer durations. Such findings seem to be typical of tissue that has been frozen prior to examination. Two cases of dead bodies found outdoors at subzero temperatures demonstrate that formerly frozen and unfrozen tissues can be distinguished histologically. The findings are examined in relation to the fundamental laws of cryobiology.

Adult↗
PubMedDate not supplied

High-presssure shift freezing. Part 2. Modeling of freezing times for a finite cylindrical model.

A comprehensive vision of the heat transfer process involved in high-pressure shift freezing (HPSF) is shown in comparison to the process at atmospheric pressure. In addition, a mathematical model to predict the freezing times is presented. This model takes into consideration the dependence of the thermophysical properties relating to temperature and pressure and the supercooling reached by liquid water at atmospheric pressure after adiabatic expansion in the HPSF process. Experimental and theoretical data appear to agree.

Freezing↗
PubMed1991

Morphometric study of glomerular slit diaphragms fixed by rapid-freezing and freeze-substitution.

The widths of slit diaphragms in rat glomeruli were quantitatively measured on electron micrographs obtained by the rapid-freezing and freeze-substitution (FS) fixation method and compared to those prepared by conventional chemical fixation procedures, such as tannic acid, glutaraldehyde and osmium tetroxide (TGO) or glutaraldehyde and osmium tetroxide (GO) fixation. When fixed by FS using 2% osmium tetroxide, glomerular slit diaphragms had widths of 33.8 +/- 3.6 nm, but when fixed by TGO or GO they had widths of 47.0 +/- 4.3 and 48.7 +/- 5.5 nm, respectively. The width of slit diaphragms was significantly narrower after cryofixation than after conventional TGO or GO fixation (P less than 0.001). Similarly, the distance between neighboring foot processes at 50 nm from slit diaphragms was significantly narrower after cryofixation (P less than 0.001). The widths were 98.6 +/- 17.1 nm after TGO fixation, 122.0 +/- 29.3 nm after GO fixation and only 54.8 +/- 18.7 nm after FS fixation. These foot processes were significantly broader after FS fixation. The foot processes were 179.2 +/- 59.4 nm in breadth after TGO fixation (P less than 0.001), 188.8 +/- 78.2 nm after GO fixation (P less than 0.01) and 235.1 +/- 87.2 nm after FS fixation. These results suggest that the cytoplasm of foot processes shrinks when the tissue is prepared by conventional chemical fixation methods, and that the broadening of slit diaphragms is an artifact separation of the margins of adjacent foot processes due to shrinkage. We propose that TGO fixation alters the structure of slit diaphragms by causing them to shrink.

Animals↗
PubMedDate not supplied

Freezing in the primary polyvinylchloride plastic collection bag: a new system for preparing and freezing nonrejuvenated and rejuvenated red blood cells.

Red blood cells were stored at 4 C in the primary bag with an integrally attached empty transfer pack so that the red blood cells could be rejuvenated or not, as desired before glycerolization and freezing. The rejuvenation and glycerol solutions were added through ports in the system. After glycerolization, the red blood cells were concentrated by centrifugation to remove the supernatant glycerol before freezing with 40% w/v glycerol in the primary polyvinylchloride (PVC) plastic container at -80 C. After thawing, the red blood cells were washed using either the Haemonetics Blood Processor 115 or the IBM Blood Processor 2991-1 or 2991-2. In each system, 50 ml of 12% sodium chloride and 1.5 to 1.6 liters of 0.9% sodium chloride-0.2% glucose-25 meq/l disodium phosphate were used. Recovery of red blood cells in vitro was 91 per cent. After three days of postwash storage at 4 C, nonrejuvenated red blood cells had a mean 24-hour posttransfusion survival of 88 per cent, and outdated-rejuvenated red blood cells a value of 81 per cent. This new system is simpler and safer than methods previously used in this laboratory, and red blood cell recovery and 24-hour posttransfusion survivals were comparable or better.

Blood Bactericidal Activity↗
PubMed1979

Membrane fusion during secretion: cortical granule exocytosis in sex urchin eggs as studied by quick-freezing and freeze-fracture.

Exocytosis of cortical granules was observed in sea urchin eggs, either quick-frozen or chemically fixed after exposure to sperm. Fertilization produced a wave of exocytosis that began within 20 s and swept across the egg surface in the following 30 s. The front of this wave was marked by fusion of single granules at well-separated sites. Toward the rear of the wave, granule fusion became so abundant that the egg surface left with confluent patches of granule membrane. The resulting redundancy of the egg surface was accommodated by elaboration of characteristic branching microvilli, and by an intense burst of coated vesicle formation at approximately 2 min after insemination. Freeze-fracture replicas of eggs fixed with glutaraldehyde and soaked in glycerol before freezing displayed forms of granule membrane interaction with the plasma membrane which looked like what other investigators have considered to be intermediates in exocytosis. These were small disks of membrane contact or membrane fusion, which often occurred in multiple sites on one granule and also between adjacent granules. However, such membrane interactions were never found in eggs that were quick-frozen fixation, or in eggs fixed and frozen without exposure to glycerol. Glycerination of fixed material appeared to be the important variable; more concentrated glycerol produced a greater abundance of such "intermediates." Thus, these structures may be artifacts produced by dehydrating chemically fixed membranes, and may not be directly relevant to the mechanism by which membranes naturally fuse.

Animals↗
PubMed1982

Freeze-fracture cytochemistry: partition of glycophorin in freeze-fractured human erythrocyte membranes.

Thin-section and critical-point-dried fracture-labeled preparations are used to determine the distribution and partition of glycophorin-associated wheat germ agglutinin (WGA) binding sites over protoplasmic and exoplasmic faces of freeze-fractured human erythrocyte membranes. Most wheat germ agglutinin binding sites are found over exoplasmic faces. Label is sparse over the protoplasmic faces. These results contrast with previous observations of the partition of band 3 component where biochemical analysis and fracture-label of concanavalin A (Con A) binding sites show preferential partition of this transmembrane protein with the protoplasmic face. Presence of characteristic proportions of WGA and Con A binding sites over each fracture face is interpreted to indicate the operation of a stochastic process during freeze-fracture. This process appears modulated by the relative expression of each transmembrane protein at either surface as well as by their association to components of the erythrocyte membrane skeleton.

Erythrocyte Membrane↗
PubMed1984

Cartilage ultrastructure after high pressure freezing, freeze substitution, and low temperature embedding. I. Chondrocyte ultrastructure--implications for the theories of mineralization and vascular invasion.

Electron microscopic examination of epiphyseal cartilage tissue processed by high pressure freezing, freeze substitution, and low temperature embedding revealed a substantial improvement in the preservation quality of intracellular organelles by comparison with the results obtained under conventional chemical fixation conditions. Furthermore, all cells throughout the epiphyseal plate, including the terminal chondrocyte adjacent to the region of vascular invasion, were found to be structurally integral. A zone of degenerating cells consistently observed in cartilage tissue processed under conventional chemical fixation conditions was not apparent. Hence, it would appear that cell destruction in this region occurs during chemical processing and is not a feature of cartilage tissue in the native state. Since these cells are situated in a region where tissue calcification is taking place, the implication is that the onset and progression of cartilage calcification are, at least partially, controlled by the chondrocytes themselves. The observation that the terminal cell adjacent to the zone of vascular invasion is viable has important implications in relation to the theory of vascular invasion. This may now require reconceptualization to accommodate the possibility that active cell destruction may be a precondition for vascular invasion.

Animals↗
PubMed1984

Cartilage ultrastructure after high pressure freezing, freeze substitution, and low temperature embedding. II. Intercellular matrix ultrastructure - preservation of proteoglycans in their native state.

The extracellular matrix of epiphyseal cartilage tissue was preserved in a state believed to resemble closely that of native tissue following processing by high pressure freezing, freeze substitution, and low temperature embedding (HPF/FS). Proteoglycans (PG) were preserved in an extended state and were apparent as a reticulum of fine filamentous threads throughout the matrix. Within this network, two morphologically discrete components were discernible and identified with the carbohydrate and protein components of PG molecules. Numerous points of contact were clearly visible between components of the PG network and cross-sectioned collagen fibrils and also between PG components and chondrocytic plasmalemmata. These observations provide direct morphological indication that such relationships may exist in native epiphyseal cartilage tissue.

Animals↗
PubMed1972

Studies on gonococcus infection. II. Freeze-fracture, freeze-etch studies on gonocci.

Gonococci have been studied by electron microscopy after freeze-cleavage, freeze-etching and the findings correlated with those obtainable through thin sectioning and negative staining. The outer membrane of the cell wall is composed of round to hexagonal subunits 80 A in diameter. This membrane is also punctuated by 80-A holes visible on the exterior of the organism and extending into the substance or through the outer membrane. Pili coursing over the surface of the organisms appear to maintain a close anatomical relationship with the cell wall. In some instances, the surfaces of the organisms are virtually covered by a layer of pili.

Cell Wall↗
PubMed1976

A copper block method for freezing non-cryoprotected tissue to produce ice-crystal-free regions for electron microscopy. I. Evaluation using freeze-substitution.

A wide variety of plant and animal tissues were prepared for electron microscopy by freeze-substitution, after rapid freezing on a liquid nitrogen cooled copper block by the van Harreveld method. Measurements were made of ice crystal size versus depth in tissues that had not been treated with any cryoprotectants. Ice crystal size increased exponentially with depth. It was confirmed that a narrow surface band increased exponentially with depth. It was confirmed that a narrow surface band (approximately 12 mum) was frozen sufficiently rapidly to prevent the formation of electron microscopically-visible ice crystals.

Animals↗
PubMed1997

Metal sandwich method to quick-freeze monolayer cultured cells for freeze-fracture.

We describe a simple quick-freezing method to obtain a large fractured plane of the plasma membrane from monolayer cultured cells. Cells were grown on thin gold foil, inverted on a thin layer of gelatin on thin copper foil, and frozen by a quick press between two gold-plated copper blocks precooled in liquid nitrogen. The frozen cell sandwich was mounted on the cold stage of a freeze-fracture device with the gold side up and was fractured by separating the sandwich with a cold fracture knife. When this technique was applied to confluent monolayer cells, large replicas of the E-face of the upper plasma membrane and the P-face of the lower plasma membrane were obtained. The present metal sandwich method is simple, does not require any expensive equipment, and provides a large fracture plane of the plasma membrane for subsequent histochemical manipulation.

Cells, Cultured↗
PubMed1989

Immunogold labeling of luciferase in the luminous bacterium Vibrio harveyi after fast-freeze fixation and different freeze-substitution and embedding procedures.

We studied the ultrastructural localization of luciferase on sections of the bioluminescent bacterium Vibrio harveyi by indirect immunogold staining, using a polyclonal antiluciferase antibody and the usual control tests, after chemical fixation or fast-freeze fixation (FFF) followed by different freeze-substitution (FS) procedures and embedding in either Epon or LR White. After liquid fixation with glutaraldehyde and paraformaldehyde and LR White embedding, labeling occurred over the cytoplasm but not over the condensed nucleoid. Epon embedding almost abolished it. FFF-FS considerably improved the morphological preservation and revealed cytoplasmic "patches" with a complex ultrastructure in Epon sections. The preservation was always less good in LR White. The patches were densely labeled, even in Epon sections, after FS in acetone. However, labeling intensity was 3.7 times greater in LR White than in Epon. With both resins, labeling diminished similarly when fixative agents were present in the FS medium. The localization of luciferase in the cytoplasm and particularly in the patches is discussed.

Freezing↗
PubMed1995

Trehalase activity and trehalose content in a freeze-tolerant yeast, Torulaspora delbrueckii, and its freeze-sensitive mutant.

Two types of trehalase activities different in the optimum reaction pH (4.3 and 6.7) were found in a freeze-tolerant yeast, Torulaspora delbrueckii D2-4, and three types of the activities at pH 4.3, 5.7, and 6.7 were found in its freeze-sensitive mutant (60B3). The pH 4.3 activities in the cell extracts of the two strains were on the same level, but the pH 6.7 activity in the strain D2-4 was about half of that in the strain 60B3. The enzyme with the pH 4.3 activity and the other two enzymes were analogous to acid and neutral trehalases, respectively, in the sensitivity to metal ions and in response to phosphorylation and dephosphorylation. The trehalose content in the strain D2-4 was three times higher than that in the strain 60B3. The change of trehalose content during growth of the strain 60B3 correlated only to the change of the pH 5.7 activity.

Adaptation, Physiological↗
PubMed1983

Clinical evaluation of freeze-dried bone allografts in periodontal osseous defects. Part III. Composite freeze-dried bone allografts with and without autogenous bone grafts.

Freeze-dried bone allografts (FDBAs) were evaluated alone and in combination with various types of autogenous bone in the treatment of periodontal osseous defects. A total of 381 defects were evaluated by surgical reentry approximately 1 year after grafting. Reentry data were compared with similar data obtained when the grafts were placed. Osseous regeneration and pocket reduction were rated as complete, greater than 50%, less than 50%, or failed. Complete or greater than 50% regeneration was considered successful. When compared with FDBAs, composite freeze-dried bone allografts/autogenous bone grafts (FDBA/ABGs) appear to offer significantly improved results in both osseous regeneration and pocket reduction. Use of composite FDBA/ABGs resulted in significant improvement in the treatment of combination one/two-wall defects and furcation involvements. A trend of improvement was seen with two-wall defects. The surgical data indicated that complete wound closure and the use of antibiotics enhanced graft success. The results also indicated that the presence of endodontically obturated teeth may be a consideration in the success or failure of the graft.

Adolescent↗