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At least 343 records · Page 19Linked to original sources

PubMed1995

Membrane skeleton restraint of surface shape change during fusion of erythrocyte membranes: evidence from use of osmotic and dielectrophoretic microforces as probes.

The role of the spectrin-based membrane skeleton in cell fusion was studied by following the condition-dependent diameter versus time expansion signature of the fusion zone in electrofused pairs of erythrocyte ghost membranes. Previous work showed that the presence of the dielectrophoresis-inducing alternating electric field, which is used to bring membranes into contact through pearl chain formation, had a detectable promoting effect on fusion zone expansion. Two new dielectrophoresis protocols were used in the present work to utilize this externally generated and controllable microforce field to probe the forces intrinsic to the system that drives the expansion of the fusion zone. First, fusion zones expanded to a greater diameter in a strong AC field compared to a weak AC field, and they expanded to a greater diameter if erythrocyte ghosts received a prior heat treatment (42 degrees C, 20 min). Furthermore, flat diaphragm fusion zones broke down into open lumen fusion zones sooner (i.e., had shorter lifetimes) when they were expanding more quickly. Second, changing the AC field strength at specific times during the fusion zone expansion led to an immediate visco-elastic response. However, shifting the AC field strength to zero after 5 s of fusion zone expansion resulted in a subsequent decrease in the average fusion zone diameter. This suggests not only that the spectrin-based membrane skeleton actually tends to prevent the rounding up process but that it may be capable of generating an antirounding force, which has broad implications for the role of the membrane skeleton in cell fusion. These results are consistent with the hypothesis that flat diaphragm fusion zones induced in heat-treated membranes were very easily stretched and that membrane-based forces that control or drive the expansion process must originate from membrane area that is outside rather than inside the fusion zone. Lastly, when an outward-directed osmotic pressure-based microforce was present at the time that erythrocyte ghosts were fused, the fusion zone diameter underwent a greater expansion in the 0-1 s interval after fusion. This suggests that an osmotic pressure-based microforce can be used to experimentally calibrate the dielectrophoretic force.

Animals↗

PubMed1997

Energy of dissociation of lipid bilayer from the membrane skeleton of red blood cells.

The association between the lipid bilayer and the membrane skeleton is important to cell function. In red blood cells, defects in this association can lead to various forms of hemolytic anemia. Although proteins involved in this association have been well characterized biochemically, the physical strength of this association is only beginning to be studied. Formation of a small cylindrical strand of membrane material (tether) from the membrane involves separation of the lipid bilayer from the membrane skeleton. By measuring the force required to form a tether, and knowing the contribution to the force due to the deformation of a lipid bilayer, it is possible to calculate the additional contribution to the work of tether formation due to the separation of membrane skeleton from the lipid bilayer. In the present study, we measured the tethering force during tether formation using a microcantilever (a thin, flexible glass fiber) as a force transducer. Numerical calculations of the red cell contour were performed to examine how the shape of the contour affects the calculation of tether radius, and subsequently separation work per unit area W(sk) and bending stiffness k(c). At high aspiration pressure and small external force, the red cell contour can be accurately modeled as a sphere, but at low aspiration pressure and large external force, the contour deviates from a sphere and may affect the calculation. Based on an energy balance and numerical calculations of the cell contour, values of the membrane bending stiffness k(c) = 2.0 x 10(-19) Nm and the separation work per unit area W(sk) = 0.06 mJ/m2 were obtained.

Biomechanical Phenomena↗

PubMed1997

Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography.

We prepared continuous porous silica rods that had silica skeletons with sizes of 1.0-1.7 microns and through-pores of 1.5-1.8 microns, and evaluated their performance as a column in reversed-phase liquid chromatography. The mesoporous silica monoliths (mesopore size: 14 or 24 nm) were derivatized to C18 phase by on-column reaction with octadecyldimethyl-N,N-diethylaminosilane. The C18 silica rods gave minimum plate heights of 10-15 microns for aromatic hydrocarbons in 80% methanol and of 20-30 microns for insulin in acetonitrile-water mixtures in the presence of trifluoroacetic acid. The performance of the silica rods at a high flow-rate was much better than that of conventional columns packed with 5 microns C18 silica particles with pores of 12 or 30 nm, especially for high-molecular-mass species. Silica rods with the smaller sized silica skeletons resulted in Van Deemter plots showing a minimum plate height linear velocity of the mobile phase and a smaller dependence of plate height on the linear velocity. Separation impedance of less than 1000 was achieved with the continuous silica columns. The higher performance and lower pressure drop of silica rods at high flow-rates compared with particle-packed columns is provided by the small silica skeletons and large through-pores.

Animals↗

PubMed1990

A mechanism of formation of protein-free regions in the red cell membrane: the rupture of the membrane skeleton.

The process of rupture and redistribution of the red cell membrane skeleton is analyzed theoretically. Following the emergence of the rupture the spectrin-actin network is redistributed on the cytoplasmic surface of the membrane bilayer. Due to the interaction of the membrane skeleton and integral proteins the redistribution of the spectrin-actin network leads to the release of purely lipid regions of the membrane. The scale of the protein redistribution caused by the rupture of the membrane skeleton and the size of the lipid domains produced depend on the shape of the membrane and the value of the electrical interaction of the membrane proteins. The lipid domains occurring as a result of the rupture and relaxation of the spectrinactin network can spontaneously increase or decrease its area. The criteria determining the conditions which result in the system's evolutions leading to the domain growth have been obtained. The character of the evolution is determined by the shape of the membrane region in which the rupture occurs as well as the relation between the effective linear tension of the rupture boundary and the modulus of elasticity of the spectrin-actin network.

Animals↗

PubMed1986

The human erythrocyte membrane skeleton may be an ionic gel. III. Micropipette aspiration of unswollen erythrocytes.

We have carried out a theoretical analysis of micropipette aspiration of unswollen erythrocytes using the protein-gel-lipid-bilayer membrane model and taking into account that the modulus of area compression of the membrane skeleton may depend on the environmental conditions. Our analysis shows that the aspiration pressure needed to obtain a certain membrane projection length is strongly dependent on the ratio between the membrane skeleton modulus of area compression and the elastic shear modulus. Our analysis therefore predicts that micropipette aspiration of unswollen erythrocytes may be a sensitive method for detection of changes in this ratio. The analysis thus also shows that micropipette aspiration of unswollen erythrocytes can not be used to determine the membrane shear modulus unless something is known about the membrane skeleton modulus of area compression.

Biophysical Phenomena↗

PubMed1988

Mechanical properties of the red cell membrane skeleton: analysis of axisymmetric deformations.

The mechanical properties of erythrocyte membrane composed of a membrane bilayer and membrane skeleton are considered. Two membrane models are described: the model of free boundaries (MFB) and the model of immobilized boundaries (MIB). In MFB, the skeleton is assumed to be attached to the bilayer at a finite number of points, whereas MIB allows the interaction of each spectrin filament with the bilayer along its whole length. For MFB an estimate was made of the mechanical strain generated in the membrane by sucking erythrocytes into a micropipette. The existence of the deformation threshold is demonstrated, below which no mechanical strain, except that of bending, appears in the membrane. Thus only deformations exceeding this threshold result in strain. The relationship between the applied tension and the height of erythrocyte "tongue" sucked into a micropipette was determined. The MIB characteristics correspond to the model of Evans: strains in the membrane are generated at any deformation, however small, i.e. the threshold is equal to zero. A basic feature of this model is quite a different distribution of the skeleton deformations in the membrane. A comparison of the theoretical models and experimental data demonstrated the possibility of either MFB or MIB occurring, depending on the characteristic measurement time.

Erythrocyte Deformability↗

PubMed2003

In situ retrocaval skeletonized right internal thoracic artery anastomosed to the circumflex system via transverse sinus: technical aspects and postoperative outcome.

BACKGROUND: The aim of this study was to investigate whether, by using the in situ right internal thoracic artery via the transverse sinus (eventually retrocaval), both the proximal and distal major branches of the circumflex system could be grafted and to evaluate the early and late outcome in these patients. METHODS: Between January 1997 and March 2002, 452 consecutive patients underwent grafting of the circumflex system with the in situ skeletonized right internal thoracic artery routed via the transverse sinus. The mean age was 62.4 +/- 10.3 years. A mean of 2.2 +/- 0.3 arterial grafts per patient were used, and 271 (60%) patients underwent total arterial myocardial revascularization. At 3 months after surgery, 86 patients (right Y or T graft) underwent echo color Doppler imaging before and after an adenosine provocative test. The mean follow-up was 27 +/- 8 months. RESULTS: The success rate of skeletonized right internal thoracic artery grafting to the circumflex system branch was 100%. There were 15 (3.4%) hospital deaths. In 116 patients who underwent postoperative angiography, the total patency rates of the right and left internal thoracic arteries were 94% and 96.6%, respectively. Strong predictors for nonfunctional internal thoracic artery grafts were a small internal thoracic artery caliber (P <.001), recipient coronary artery diameter less than 1.5 mm (P =.012), stenotic lesions of less than 60% (P =.016), and diffuse stenotic lesions (P =.015) of the recipient coronary artery. In 86 patients who underwent postoperative echo color Doppler imaging, the flow reserves at the main stem of the left and right internal thoracic arteries were 2.24 +/- 0.5 and 2.48 +/- 0.6, respectively. Cumulative actuarial survival at 3 years was 96.3%, and event-free cumulative survival was 93%. The Cox model revealed a left ventricular ejection fraction of less than 35% (P =.016), age greater than 70 years (P =.025), New York Heart Association grade greater than III (P =.0019), nontotal arterial myocardial revascularization (P =.002), and the preoperative presence of more than 1 ischemic area (P <.001) as strong predictors for poor overall cumulative event-free survival. CONCLUSIONS: The skeletonized right internal thoracic artery, placed via the transverse sinus and eventually retrocaval, can reach most branches of the circumflex system and is associated with an excellent patency rate. The predictors for poor overall event-free survival seem to be similar to those of the general population undergoing conventional coronary artery bypass grafting. Use of bilateral internal thoracic arteries and in situ right internal thoracic artery grafting via the transverse sinus offers the possibility of various configuration constructions, making possible total arterial myocardial revascularization with a minimum number of arterial conduits.

Adult↗

PubMed1983

Tannic acid improves the visualization of the human erythrocyte membrane skeleton by freeze-etching.

The effect of fixatives on the membrane skeleton underlying the human erythrocyte membrane was examined by freeze-etching. An anastomosing fibrillar network was readily observed on the protoplasmic surface of the erythrocyte membrane treated with tannic acid. Such structure was much less defined in unfixed membrane or membrane fixed with glutaraldehyde or glutaraldehyde followed by osmium tetraoxide. Tannic acid caused a marked increase in diameter of the fibrillar components of the membrane skeleton and of the protoplasmic surface particles of inside-out vesicles prepared by alkali treatment but did not affect the size of intramembranous particles seen on fracture faces nor the appearance of exoplasmic surfaces. The improved visualization of the membrane skeleton after treatment with tannic acid resulted from interactions between tannic acid and exposed membrane proteins.

Erythrocyte Membrane↗

PubMed2001

Glycoprotein Ib/IX/V binding to the membrane skeleton maintains shear-induced platelet aggregation.

The extracellular domain of glycoprotein (Gp) Ibalpha serves as the von Willebrand factor (vWf) receptor that triggers shear stress-dependent platelet aggregation. Its intracellular domain associates with actin-binding protein-280 (filamin 1a) that binds directly to filamentous actin, thereby linking the membrane skeleton to GpIbalpha. We examined the functional significance of GpIbalpha interactions with actin during platelet aggregation in response to 120 dyn/cm(2) shear stress. Lysates of resting and sheared platelets were centrifuged at approximately 13,000xg for 15 min, and GpIbalpha was immunoprecipitated from the lysate supernatant. GpIbalpha and coimmunoprecipitated proteins were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotted with antibodies specific for GpIbalpha and actin. We observed a significant increase in the amounts of actin coimmunoprecipitating with GpIbalpha as platelets aggregated in response to shear stress. Actin/GpIbalpha interactions reached a maximum after 90 s of shear stress. Monoclonal antibody (mAb) blockade of vWf binding to GpIbalpha inhibited shear stress-induced platelet aggregation and actin associating with GpIbalpha. Pretreatment of platelets with cytochalasin D resulted in the inhibition of actin binding to GpIbalpha in sheared platelets and in an increase in the rate and magnitude of platelet disaggregation. These data indicate that shear stress causes changes in the association between GpIbalpha and the actin-based membrane skeleton. The increased interaction between GpIbalpha and the actin-based membrane skeleton results from shear-induced vWf binding to GpIbalpha and is mechanoprotective in that it maintains shear-induced aggregation of activated platelets.

Actins↗

PubMed2002

Automatic identification by 13C NMR of substituent groups bonded in natural product skeletons.

The aim of this paper is to present a procedure that utilizes 13C NMR for identification of substituent groups which are bonded to carbon skeletons of natural products. For so much was developed a new version of the program MACRONO, that presents a database with 161 substituent types found in the most varied terpenoids. This new version was widely tested in the identification of the substituents of 60 compounds that, after removal of the signals that did not belong to the carbon skeleton, served to test the prediction of skeletons by using other programs of the expert system SISTEMAT.

Biological Factors↗

PubMed1998

A spectrin membrane skeleton of the Golgi complex.

The existence of a Golgi-localized membrane cytoskeleton has been revealed by the identification of two major components of the spectrin membrane skeleton, spectrin and ankyrin, that associate with the Golgi complex. Golgi spectrin was identified with an antibody specific for the beta-subunit of the erythroid isoform of spectrin (beta1Sigma1). This antibody recognizes a 220 kDa polypeptide that localizes to discrete regions of the Golgi complex and associates with Golgi membranes in a Brefeldin A sensitive manner. Two isoforms of Golgi ankyrin have been identified: a 119 kDa form (AnkG119) which represents a truncated, alternatively spliced isoform of a recently cloned novel ankyrin of the nervous system AnkG, and a larger 195 kDa ankyrin (Ank195) that cross-reacts with antibodies to erythrocyte ankyrin. A Golgi localized membrane skeleton composed of these unique membrane skeleton isoforms could serve a variety of important functions, including the maintenance of Golgi structural organization and the formation of discrete membrane domains within Golgi compartments.

Animals↗

PubMed2003

Anomalies in the developing neural and visceral head skeleton of the Australian lungfish, Neoceratodus forsteri.

Several anomalies occur in the developing neural and visceral head skeleton of young specimens of Neoceratodus forsteri that have been reared under laboratory conditions. These include anomalies of the basicranium and its derivatives, aberrations of the anterior mandible and hyoid apparatus, and abnormalities in the articulation of the jaws and the elements that produce them. Apart from the occasional absence of the basihyal, and failure of the quadrate processes to form, the anomalies are not deficiencies. Most involve malformations of parts of the neurocranium and visceral skeleton, inappropriate articulations or fusions between elements, disunity in structures that are normally fused and the appearance of supernumerary elements. The incidence of chondral anomalies, generally higher than aberrations that occur in the dermal skeleton in juvenile lungfish, ranges from 1-10% in laboratory reared individuals that have not been subjected to experimental interference. The anomalies differ from those found in many amphibian populations, in the field and in the laboratory, because they involve the cranium, and not the limbs, and the lungfish have not been exposed to the factors that cause anomalies in the amphibians. It is unlikely that the existence of those anomalies, if it is reflected in the wild population, places a selective pressure on the lungfish, because, in a normal season, less than 1% of the total number of eggs produced survive to be recruited into the adult population.

Animals↗

PubMed1998

Sequential order of appearance of ossification centers in the opossum Didelphis albiventris (Didelphidae) skeleton during development in the marsupium.

Pouch-young of the opossum Didelphis albiventris were studied. They were removed from the marsupium at a crown-rump length (CRL) of 9.0 to 100.0 mm and submitted to differential staining of the bone and cartilage. Newborn D. albiventris of 9.0 to 10.0 mm CRL have a cartilaginous skeleton, with no macroscopic evidence of ossification. In 10.5 to 13.0 mm CRL pouch-young, ossification occurs in the bones surrounding the oral cavity, clavicle, ribs, cervical and thoracic vertebrae and thoracic limbs, structures necessary to ensure the survival and maintenance of the newborn in the marsupium. Ossification of most of the skull begins in 15.5 to 16.0 mm CRL pouch-young. The ossification in the pelvis and the pelvic limbs is observed at 18.0 mm CRL and in the sternum and the epipubic bone at 25.0 to 28.0 mm CRL. Most of the skeleton is ossified in 45.0 to 58.0 mm CRL pouch-young, except in the carpus, tarsus and epiphyses of the long bones where ossification occurs in 60.0 to 100.0 mm CRL pouch-young. In the skeleton of D. albiventris the omosternum, haemal arches, prepollex, prehallux and parafibula, are present. These are inconstant or absent elements in eutherian mammals.

Aging↗

PubMed2001

Composite arterial grafting with double skeletonized internal thoracic arteries.

OBJECTIVES: Composite arterial grafting is a surgical technique for arterial myocardial revascularization, in which free arterial conduits are proximally anastomosed end-to-side to an intact internal thoracic artery (ITA). This report describes technical aspects and results of composite grafting using bilateral skeletonized ITAs. METHODS: From April 1996 to February 1999, 1057 patients underwent coronary artery bypass grafting (CABG) using bilateral skeletonized internal thoracic arteries. In 600 of them (57%), composite arterial grafting was performed. There were 452 men and 148 women. The mean age was 69 +/- 7 years. Two-hundred and six patients (34%) were diabetics, 84 (14%) had severe left ventricular dysfunction (ejection fraction of < 35%), and 26 (4.3%) underwent emergency operations. In 574 patients, the right ITA was used as a free graft connected to the in-situ left ITA. In 26, the free left ITA was attached to the in-situ right ITA, and in 38, mini-composite grafts (free distal left ITA on the left ITA, or free distal right ITA on the right ITA) were constructed. The average number of grafts was 3.0/patient (range, 2--6). RESULTS: The operative mortality was 2.8% (n = 17), and there were ten (1.7%), deep sternal wound infections. The mean follow-up was 25 months (range, 14--36 months). The 3-year survival was 92.5%. Ninety-seven percent of the surviving patients were angina-free. CONCLUSIONS: We currently perform this surgery routinely in most patients referred for CABG, and regard bilateral skeletonized internal thoracic arteries as the most appropriate arterial conduits for the composite technique.

Adult↗

PubMed1996

Bilateral skeletonized mammary artery grafting: experience with 560 consecutive patients.

OBJECTIVE: To test the hypothesis that the skeletonized technique of harvesting the internal thoracic artery improves the surgical results of bilateral internal thoracic artery grafting, we reviewed our 7-year experience with this technique. METHODS: Between July 1987 and December 1994, 560 patients received bilateral internal thoracic artery grafts and 236 additional grafts (average 2.6 +/- 0.6 anastomoses per patient). There were 515 men (92%) and the average age was 56.9 +/- 8.8 years. There were 63 diabetic patients (11.3%). During harvesting, the internal thoracic arteries were always totally skeletonized from the surrounding tissues without the use of electrocautery. RESULTS: Postoperative complications included reoperation for bleeding, 17 patients (3%), phrenic nerve paresis, 17 patients (3%), acute respiratory distress syndrome, 9 patients (1.6%), digestive complications, 8 patients (1.4%), neurologic complications, 6 patients (1.1%), and sternal complications, 6 patients (1.1%). No wound complications were observed in diabetic patients. The hospital mortality rate was 1.6% (9 patients, 2 cardiac causes). The early patency of internal thoracic artery grafts was 97.9%. Follow-up averages 29 +/- 20 months. There were 14 late deaths (4 cardiac causes). Angina recurred in 51 patients and the maximal stress test was abnormal in 47 patients. CONCLUSION: Bilateral internal thoracic artery grafting with skeletonized harvesting carried low post-operative mortality and morbidity and therefore it could be applied routinely without the fear of increased complication rate.

Adult↗

PubMed1997

Red cell membranes of ankyrin-deficient nb/nb mice lack band 3 tetramers but contain normal membrane skeletons.

The role of ankyrin in the formation and stabilization of the spectrin-based skeletal meshwork and of band 3 oligomers was studied by characterizing, in nb/nb mouse red cells, the effect of ankyrin deficiency on skeletal ultrastructure, band 3-skeleton associations, and band 3 oligomeric states. Despite severe ankyrin deficiency, nb/nb mouse red cell skeletal components formed a relatively uniform two-dimensional hexagonal array of junctional complexes cross-linked by spectrin tetramers. Treatment of nb/nb ghosts with the nonionic detergent C12E8 (octaethylene glycol n-dodecyl monoether) resulted in nearly complete extraction of band 3. The extracted band 3 was present exclusively as band 3 dimers. Fluorescence photobleaching recovery and polarized fluorescence depletion measurements showed increases in the laterally (33% vs 10%) and rotationally (90% vs 76%) mobile fractions of band 3 in intact nb/nb compared to control red cells. The rotational correlation time of the major fraction of band 3 molecules was 10-fold shorter in nb/nb compared to control red cells, indicating a significant relaxation of rotational constraints in nb/nb cells. These data suggest that, although ankyrin plays a major role in strengthening the attachment of the skeleton to the membrane bilayer, ankyrin is not required for the formation of a stable two-dimensional spectrin-based skeleton. The absence of band 3 tetramers in the membrane of ankyrin-deficient red cells suggests that ankyrin is required for the formation of stable band 3 tetramers.

Animals↗

PubMed2005

Unsaturated diterpenoids with a novel carbocyclic skeleton from Salvia xalapensis.

Two diterpenoids with an unprecedented carbocyclic skeleton, salvixalapadiene (3) and isosalvixalapadiene (4), have been obtained from the leaves of Salvia xalapensis. The rearranged skeleton of these products may be derived biogenetically from a salvigenane precursor. In addition, two new rearranged diterpenoids (1 and 2) belonging to already known skeletons were isolated. The structures of the new compounds (1-4) were elucidated on the basis of spectroscopic data interpretation.

Diterpenes↗

PubMed2006

Minor sesquiterpenes with new carbon skeletons from the brown alga Dictyopteris divaricata.

Five minor sesquiterpenes (1-5) with two novel carbon skeletons, together with a minor new oplopane sesquiterpene (6), have been isolated from the brown alga Dictyopteris divaricata. By means of spectroscopic data including IR, HRMS, 1D and 2D NMR, and CD, their structures including absolute configurations were assigned as (+)-(1R,5S,6S,9R)-3-acetyl-1-hydroxy-6-isopropyl-9-methylbicyclo[4.3.0]non-3-ene (1), (+)-(1R,3S,4S,5R,6S,9R)-3-acetyl-1,4-dihydroxy-6-isopropyl-9-methylbicyclo[4.3.0]nonane (2), (+)-(1R,3R,4R,5R,6S,9R)-3-acetyl-1,4-dihydroxy-6-isopropyl-9-methylbicyclo[4.3.0]nonane (3), (+)-(1S,2R,6S,9R)-1-hydroxy-2-(1-hydroxyethyl)-6-isopropyl-9-methylbicyclo[4.3.0]non-4-en-3-one (4), (-)-(5S,6R,9S)-2-acetyl-5-hydroxy-6-isopropyl-9-methylbicyclo[4.3.0]non-1-en-3-one (5), and (-)-(1S,6S,9R)-4-acetyl-1-hydroxy-6-isopropyl-9-methylbicyclo[4.3.0]non-4-en-3-one (6). Biogenetically, the carbon skeletons of 1-6 may be derived from the co-occurring cadinane skeleton by different ring contraction rearrangements. Compounds 1-6 were inactive (IC(50) > 10 mug/mL) against several human cancer cell lines.

Drug Screening Assays, Antitumor↗