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Biomedical subjects

A Walter

Publications and source records attributed to A Walter.

At least 19 recordsLinked to original sources
PubMed1992

Active respiratory syncytial virus purified by ion-exchange chromatography: characterization of binding and elution requirements.

Two viruses, respiratory syncytial virus (RSV) and vesicular stomatitis virus (VSV) were used to evaluate viral purification by an affinity resin column (Matrex Cellufine Sulfate (MCS); Amicon Division, WR Grace & Co.). Viable RSV was purified significantly from crude cell lysate by a single pass through a column containing the anionic MCS resin. Most cell protein and albumin eluted from the MCS resin with phosphate buffered saline (PBS) but RSV eluted at high ionic strength, i.e., greater than or equal to 0.6 M NaCl. Further purification was possible by sucrose step gradient centrifugation. The RSV prepared by column purification or by column plus sucrose gradient separation was both intact and infective. RSV and pure samples of VSV were used to optimize ionic strength and salts for elution from the MCS column: 0.8 M NaCl removed most of the viral protein. The capacity of the MCS gel for RSV or VSV was found to be about 0.6-0.8 mg viral protein per ml of hydrated resin. Detergent-solubilized viral membrane proteins bound to the MCS resin in 0.145 M NaCl and eluted with higher salt concentrations. Thus, this resin also may be a useful aid for relatively gentle purification of these proteins.

Centrifugation, Density Gradient↗
PubMed1992

Ion channels in single bilayers induced by rat connexin32.

The gap junction channel mediates an important form of intercellular communication, but its detailed study is hindered by inaccessibility in situ. We show here that connexin32, the major protein composing junctional channels in rat liver, forms ion channels in single bilayer membranes. The properties of these reconstituted connexin32 channels are characterized and compared with those of gap junction channels. The demonstration that connexin32 forms channels in single membranes has implications for assembly and regulation of junctional channels, and permits detailed study of the gating, permeability and modulation of this channel-forming protein.

Animals↗
PubMed1992

Maternity and medicinal plants in Vanuatu. I. The cycle of reproduction.

Ethnobotanical data collection to select pharmacologically active species was carried out within a clearly defined therapeutic context: those plants used during the course of a woman's reproductive life. Extensive bibliographical and field data collection and cross-examination of the information thus gathered have provided us with a clearer picture of the effectiveness of these plant species. Various concepts, behaviours and practices relating to menstruation, pregnancy, birth and birth control were examined in detail from an ethnopharmacological point of view. A list of selected species of particular interest is proposed for further study.

Family Planning Services↗
PubMed1992

On the material and the tribology of alumina-alumina couplings for hip joint prostheses.

The yearly sphericity deviation ranged from 0.03 mu to 3.7 mm in 48 retrieved implants with alumina--alumina bearing balls and cups. Excessive amounts of wear are predominantly design dependent or caused by malalignment. But the abrasion phenomena occurring in the cup centers and in the corresponding ball areas are related to unfavorable function zones. The influence of the lubricating gap geometry as studied in laboratory tests shows the form of sphericity deviations to be of decisive importance for wear and friction, if extended over small angles. Then, the contact stresses attributable to the actual effective curvatures of the bearing exceed the resistance to abrasion of the material under boundary lubrication conditions. There are remarkable differences between the early and actual material quality. Based on the state of knowledge of material aspects of wear criteria for the optimization of material and design, promising tolerable wear rates may be achieved.

Aluminum Oxide↗
PubMed1991

Potassium channel activation, hyperpolarization, and vascular relaxation.

1) Numerous compounds and changes in physical state functions shift the membrane potential of vascular smooth muscle to more negative values. The consequence is a vasodilatation because Ca2+ channels are closed. K+ channel opening frequently causes the hyperpolarization. 2) Acidification of the blood substitute solution, a fall in O2 partial pressure, and an increase in blood flow dilate arterial vessels. Acidosis is associated with a rise in K+ permeability and a simultaneous fall in Na+ permeability. Prostacyclin has a 20-30% share, and EDHF a 70-80% share in hypoxic vasodilatation. Experiments with iloprost (PGI2 analogue) confirmed the K+ channel opening properties of this drug. A voltage-dependent K+ channel and a Ca(2+)-activated K+ channel, via the influence of cA-PK or cG-PK, are responsible for the hyperpolarization with iloprost and with oxygen deficiency. 3) With 23Na+ nuclear magnetic resonance techniques, it has been demonstrated that with flow-dependent vasodilatation, proteoheparan sulphate integrated in the membrane of endothelial cells possibly served as a "flow sensor". With an external strain, such a compound can go from a randomly coiled state to an oriented state. Based on these viscoelastic properties, heparan sulphate proteoglycan is present as a random coil under "no flow" conditions and as an unfurled filament structure with increasing flow. This conformational change produces additional anionic binding sites to which Na+ ions of the blood are bound. A membrane hyperpolarization could be directly initiated by this Na+ binding via the protein fraction within the macromolecule or via a change in zeta-potential. Therefore, these ions can trigger the signal transduction for a vasodilatory vessel reaction. Decrease in flow is followed by a structural change of the macromolecule towards coil conformation, a release of Na+ ions and, thus, an interruption of the signal chain. 4) Cicletanine, aqueous garlic extract, and ajoene cause a concentration-dependent membrane hyperpolarization and are potent vasodilators. A cicletanine concentration, which is attained by the dosage given to patients, is sufficient to produce these effects. Under noradrenaline, the cicletanine effect is amplified. Aqueous garlic extract and ajoene exert a hyperpolarizing and vasodilating influence even in a concentration which may occur in the extracellular space by the administration of a single garlic clove. 5) The stationary activation curve "developed force vs. membrane potential" satisfactorily explains the effects of K+ channel openers. The tight electromechanical coupling expressed by this curve comprises a 50% vasorelaxation for a 2.5 mV hyperpolarization. In the linear part of the curve, the coupling ratio is 5.1 mV/g.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Measuring of the in-vitro assembly of microtubules by dynamic light scattering.

The kinetics of in-vitro assembly of microtubule protein (MTP) to microtubules (MTs) was followed under various conditions (temperature, GTP, ultrasonic treatment) by dynamic light scattering (DLS) and turbidimetric measurements. The results of both methods roughly coincide, but DLS additionally allows to differentiate between MTs and aggregates and to follow their growth. The complexity of these investigations, however, causes serious restrictions in the interpretation of the DLS data.

Animals↗
PubMed1991

[Acute methanol poisoning--a review and a case report].

Acute methanol intoxications are infrequent among accidental or suicidal intoxications today. The characteristic findings are illustrated by a review. Mainly, the methanol metabolites formaldehyde and formic acid are of toxicologic importance and cause the dominant central nervous and ocular symptoms. The principal therapeutic procedures include gastric lavage, induced vomiting, titrated correction of acidosis with sodium bicarbonate, administration of ethanol, folic acid and, especially, the secondary detoxication with peritoneal--or better--haemodialysis. The therapeutic measures must be started quickly and carried out consequently to improve the prognosis of methanol intoxication and to decrease the frequency of serious late complications like ophthalmologic and neurologic lesions. Our own medical management is described by a case report treated successfully.

Adult↗
PubMed1990

Membrane solubilization with and reconstitution from surfactant solutions: a comparison of phosphatidylserine and phosphatidylcholine interactions with octyl glucoside.

Most structural and functional studies of membrane proteins eventually require that the protein be solubilized from its original membrane, isolated and reconstituted into a membrane composed of native or specific phospholipids. The conditions comprising a successful reconstitution protocol often seem both arbitrary and elusive. The solubilization steps as the neutral surfactant octyl glucoside (OG) is added to the negatively charged lipid phosphatidylserine (PS) were followed by several optical techniques. Vesicle leakage, changes in resonance energy transfer between lipid probes and micelle formation were determined as a function of (PS) and temperature. The (OG) needed at these transitions was linear with (PS) so that average compositions and the free (OG) could be calculated for each point. More OG is needed to solubilize at 15 compared to 35 degrees C reflecting the temperature dependence of pure OG solubility. Although similar, the average compositions of the mixed surfactant-lipid structure and their temperature dependence were not identical to similar points determined for egg phosphatidylcholine and OG.

Animals↗
PubMed1990

Solubility properties of the alkylmethylglucamide surfactants.

The critical micelle concentration (CMC) and the ability to solubilize and form vesicles from phospholipids are important criteria for the selection of a surfactant for reconstitution protocols. The CMC and its temperature dependence were determined for an homologous series of alkylmethylglucamides (MEGA-8, MEGA-9, MEGA-10). Each detergent was added continuously from a concentrated solution to a saline buffer with the environment-sensitive fluorescent probe ANS, held in a thermojacketed cuvette; ANS fluorescence increases at the CMC. The CMCs at 25 degrees C were 51.3, 16.0 and 4.8 mM for MEGA-8, MEGA-9 and MEGA-10. The free energy change for transfer to a micellar environment per -CH2- was -740 cal/mol, similar to other alkyl series. The CMCs decreased slightly with increasing temperature (T = 5-40 degrees C) for MEGA-9 and MEGA-10 while that of MEGA-8 was virtually insensitive to temperature in this range. MEGA-9 solubilization of egg PC in aqueous solutions was determined as a function of [PC] and temperature. The lamellar-micellar phase boundaries were determined by simultaneous 90 degrees light scattering and the resonance energy transfer using the headgroup labeled lipid probes NBD-PE and Rho-PE. The [MEGA-9] at solubilization was linear with [PC]; the MEGA-9 to egg PC ratio in the structures at optical clarity was 2.3 while the monomeric [MEGA-9] was 14.3 mM or slightly lower than the CMC at 25 degrees C. Solubilization of egg PC by MEGA-9 was somewhat more temperature-dependent than the CMC of this detergent. Vesicles formed from MEGA-9 tended to be multilamellar. MEGA-9 is clearly different from octyl glucoside, despite its chemical similarity, in terms of its temperature sensitivity and vesicle forming characteristics.

Fatty Acids↗
PubMed1990

Mapping of neuropeptide Y-like immunoreactivity in the human forebrain.

By means of immunohistochemistry the distribution of neuropeptide Y (NPY)-containing neurons and fibres was determined in the human forebrain on the basis of frontal paraffin sections from six individuals of different biological age. NPY was located in abundance in telencephalic cortical and subcortical structures like the striatum, the amygdaloid body and the substantia innominata. Variations in the distribution of immunoreactivity were observed and correlated with distinct subdivisions and structural elements of the basal forebrain region identified by Weigert or Nissl-stained neighbouring sections. The diencephalon was characterized by a relative paucity of labeled cells which were mostly confined to the area of the Nc. infundibularis and the median eminence while fibers were widely distributed in high density in most hypothalamic subnuclei except for the supraoptic nucleus. A periventricular zone of high fibre immunoreactivity was observed in the thalamus. NPY distribution in the developing brain was characterized by the finding of numerous labeled perikarya in the subcortical white matter and by far higher densities of labeled cells in the striatum as compared to the adult brain.

Adult↗
PubMed1990

[Late occlusive thrombosis of mitral prosthesis with sinus rhythm. Report of two surgically treated patients].

Two cases are reported of late occlusive thrombosis of a mitral bioprosthesis with sinus rhythm. Two men were concerned (40 and 54 years of age), hospitalized for acute pulmonary oedema which was resistant to medical treatment, 3 years after replacement of a mitral valve (Carpentier Edwards No. 31 and Liotta No. 25). Catheterization showed that in both cases there was an average transmitral holodiastolic gradient greater than 25 mmHg. Emergency surgery revealed two anatomical forms of occlusive thrombosis: in one case, a localized red thrombus hindered the opening of a valve cusp; in the other, exuberant fibrin deposits lined the ventricular face of the valve cusps. There were no signs of degeneration of the bioprostheses and, in particular, there was no calcification. Both patients were asymptomatic 1.5 years and 3 years respectively after their operations. Late occlusive thromboses of mitral bioprostheses are exceptional (13 detailed cases collected from the literature).

Adult↗
PubMed1989

Temperature dependence of the vesicle-micelle transition of egg phosphatidylcholine and octyl glucoside.

The temperature dependence of octyl glucoside micellization was determined and compared to the phase behavior of the octyl glucoside--egg phosphatidylcholine (PC) mixed system in excess water to help elucidate the process of vesicle formation from mixed surfactant-phospholipid micelles. The critical micelle concentration of octyl glucoside (OG) was determined from the sharp increase of ANS fluorescence at micellization in an NaCl buffer at temperatures ranging from 5 to 40 degrees C. The cmc decreased with increasing temperature from 31 mM at 5 degrees C to 16 mM at 40 degrees C. A similar but less steep temperature dependence is observed for the solubilization of egg PC vesicles by OG as monitored by the surfactant-dependent changes in (1) solution turbidity and (2) the resonance energy transfer between NBD-PE and Rho-PE incorporated in the vesicles. These assays identify two breakpoints, most likely the boundaries of the cylindrical micelle and spheroidal micelle coexistence region. The [OG]aq values at these two breakpoints have similar temperature dependencies. However, the cylindrical mixed micelles at the boundary have nearly identical OG:PC ratios over the temperature range studied, whereas the spheroidal mixed micelles have relatively more OG at the higher temperatures (OG:PC ratio increases from 2.92 to 3.72 between 5 and 35 degrees C). Estimation of the acyl volume to surface area ratio for the compositions observed suggests that this parameter remains constant over temperature. The spheroidal mixed micelles, but not the cylindrical PC-OG micelles, exhibit ideal mixing between the two components at all temperatures (5-35 degrees C). This temperature sensitivity may be utilized to improve the efficacy of membrane protein reconstitution.(ABSTRACT TRUNCATED AT 250 WORDS)

Colloids↗
PubMed1989

Transport-specific isolation of large channels reconstituted into lipid vesicles.

To develop a technique for purifying and identifying pore-forming membrane proteins, we used a transport-specific increase in buoyant density to select for lipid vesicles containing voltage-dependent anion channels (VDAC). Monodisperse, single-walled vesicles were formed by gel filtration from a detergent-solubilized mixture of lipid and protein in a urea buffer. The vesicles were layered on a linear iso-osmolar density gradient formed of urea and sucrose buffers. Since VDAC is open at zero trans-membrane voltage and is permeable to urea and sucrose, vesicles containing functional VDAC should become more dense as sucrose enters and urea leaves, while those lacking open channels should maintain their original density. Vesicles formed in the absence of VDAC migrated to a characteristic density, while vesicles formed in the presence of VDAC fractionated into two populations in the gradients, one migrating to the same density as the vesicles formed without VDAC, and one at a significantly greater density. In contrast to the lower density vesicles, the higher density vesicles showed a high permeability to calcein, and contained functional VDAC channels (shown by electrophysiological recordings following fusion with a planar bilayer). Thus, vesicles containing open channels were separable from those that did not by a transport-specific shift in density. This technique may be useful for the enrichment of channels of known permeability properties from impure material.

Biological Transport↗
PubMed1989

Structural differences between histone H1 molecules from sea urchin (Strongylocentrotus intermedius) sperm and calf thymus: hydrodynamic and c.d. studies.

Comparative sedimentation, diffusion and circular dichroism (c.d.) measurements have been performed on two histones H1 from sperm of the sea urchin Strongylocentrotus intermedius (H1S) and from calf thymus (H1T), at a high salt concentration of M NaCl. Both the Stokes radius and the frictional ratio derived from the hydrodynamic parameters were found to be somewhat smaller for H1S than the corresponding values for H1T. In view of the considerably higher molar mass of H1S compared with that of H1T, this result indicates that H+S in 2 M NaCl has a more compact conformation than H1T, probably due to a higher degree of secondary structure in the flanking domains of H1S. The c.d. measurements likewise show that H1S has a higher content of ordered structures than H1T. Model considerations indicate that the C-terminal tail of H1S is the main candidate for accommodation of these additional secondary structure regions.

Animals↗
PubMed1989

Vesicle-micelle transition of phosphatidylcholine and octyl glucoside elucidated by cryo-transmission electron microscopy.

Vesicle-micelle transition structures of egg phosphatidylcholine (PC) and octyl glucoside (OG) mixtures were observed in the vitrified hydrated state by cryo-transmission electron microscopy (cryo-TEM) and correlated with the macroscopic and molecular changes previously associated with micellization monitored by 90 degrees light scattering and resonance energy transfer between fluorescent lipid probes. Several distinct structural changes occurred as OG was added to the PC vesicles. First, the average vesicle size decreased from 160 nm to less than 66 nm with no apparent change or decrease in optical density (OD). Then, associated with a small rise in OD, samples with open vesicles were observed coexisting with pieces of lamellae and long cylindrical micelles; more micelles were seen at higher [OG]. This mixture of vesicles and cylindrical micelles occurred in the region of the phase diagram previously attributed to vesicle opening, and possibly vesicle size increase. At higher [OG], small spheroidal micelles coexisting with cylindrical micelles correlated with a decrease in OD and changes in the fluorescence signal. At high [OG] when the solution appeared clear, spheroidal micelles were the dominant structure. By using cryo-TEM, a technique which preserves the original microstructure of fluid systems and provides direct images at 1 nm resolution, we have elucidated the vesicle-micelle transition and identified intermediates not known previously in the PC/OG system.

Cell Membrane↗