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Biomedical subjects

A Palm

Publications and source records attributed to A Palm.

At least 19 recordsLinked to original sources
PubMed2000

Steroid profiles determined by capillary electrochromatography, laser-induced fluorescence detection and electrospray-mass spectrometry.

Macroporous, monolithic capillary electrochromatography (CEC) columns, featuring a hydrophobic stationary phase, have been applied to the separations of steroids with good column efficiency. Using isocratic and gradient elution runs, mixtures of neutral or conjugated steroids could be resolved. While dansylated ketosteroids were detectable through laser-induced fluorescence at attomole levels, the CEC columns coupled to electrospray-ion-trap mass spectrometry featured femtomole detection limits.

Electrophoresis, Capillary↗
PubMed2000

Deletion of the GPG motif in the HIV type 1 V3 loop does not abrogate infection in all cells.

The three amino acids glycine, proline, and glycine (GPG) constitute a conserved motif at the center of the V3 loop of HIV-1 surface glycoprotein 120. It has been indicated that deletion of this GPG motif is lethal for viral infectivity and abrogates the ability of the virus to form syncytia. In the present work, we studied the effects of GPG deletion on viral infectivity, cell tropism, syncytium formation, and initiation of apoptosis by constructing a mutant provirus based on the infectious clone pBRu-2. Successful infection and replication of GPG-deleted virus were detected in MT-2 cells, although the mutant virus showed lower infectivity. Infection could also be observed in the C8166, C91-PL, Molt-3, and THP-1 cell lines, and in PBMC-derived dendritic cells (DCs), but not in CEM-SS, HUT78, H9, Jurkat, and U937 cell lines or in PBMCs. Mutant virus also induced syncytia and apoptosis in the MT-2 cells. An intact GPG motif is probably necessary for unimpaired induction of fusion in some HIV-1-permissive cells. However, once the virus enters the cells, the GPG sequence does not seem to be indispensable for syncytium formation or apoptosis induction in MT-2 cells. Our data also imply that cell surface molecules other than CD4 and CXCR4 may be involved in entry of the GPG-deleted virus.

Amino Acid Motifs↗
PubMed2000

Calibration of plane-parallel chambers and determination of p(wall) for the NACP and Roos chambers for 60Co gamma-ray beams.

Procedures for the calibration and use of plane-parallel ionization chambers in high-energy electron and photon beams have been given in the international code of practice IAEA TRS-381. In the present work, plane-parallel ionization chambers of the type PTW-34001 Roos and Scanditronix NACP02 have been calibrated using two N(K)-based procedures. For the NACP chamber the difference between the N(D,air) chamber factors determined in an electron beam and in a 60Co gamma-ray beam, respectively, is of the same magnitude as the experimental uncertainty. Results for the PTW Roos chambers, however, do not agree, in accordance with recent findings of other authors. The value determined in a 60Co gamma-ray beam is questioned and the reason for the discrepancy assigned to the correction factor for the perturbation due to the chamber wall, p(wall). New values of p(wall) have been experimentally determined by comparing absorbed dose measurements based on air-kerma and absorbed dose to water calibration procedures. A new p(wall) factor for the Roos chamber in 60Co gamma-ray beams in water (1.009+/-0.6%) was derived as the weighted average of the different determinations. The value is not significantly higher than the p(wall) factor given in TRS-381 (1.003+/-1.5%), but the combined standard uncertainty is reduced. The chamber to chamber variation for six commercial PTW Roos chambers and a Roos prototype was found to be very small.

Air↗
PubMed2000

Influence of sulphuric acid contaminants on Fricke dosimetry.

The sulphuric acid used for the preparation of the Fricke dosimeter solution may contain trace impurities that can affect the yield of ferric ions. Two methods, pre-irradiation or oxidation with hydrogen peroxide, have been proposed to reduce the influence of these impurities. Fricke users sometimes omit this treatment. In the present work Fricke solutions prepared from six different brands and qualities of sulphuric acid were compared in order to study any influences of the acid on the ferric ion yield. It was shown that the use of analytical grade sulphuric acid from one manufacturer resulted in a reduction of the ferric ion yield of about 5% at an absorbed dose of approximately 20 Gy. If this solution were to be used for an absolute dose determination together with epsilon(m) G values from the literature the absorbed dose would be underestimated by the same amount.

Cobalt Radioisotopes↗
PubMed1999

Experimental study on the influence of the central electrode in Farmer-type ionization chambers.

In the IAEA TRS-381 protocol, k(cel) and p(cel) account for the central electrode perturbation during the air kerma chamber calibration and the in-phantom measurements. The values of these correction factors are based mainly on Monte Carlo simulations. In the present work experimental data on k(cel) and p(cel) for the NE-2571 chamber is provided, relative to a graphite electrode. In addition, the relative influence of the 3 mm diameter A-150 central electrode of the NE-2581 chamber is studied. The experimentally determined value of k(cel) for a 1 mm aluminium electrode is 1.008 +/- 0.2%, and of p(cel) in photon and electron beams 0.993 +/- 0.2% and 0.997 +/- 0.2% respectively. The experimental data and the Monte Carlo simulations agree to within 0.2%. No significant influence of the A-150 central electrode diameter on the absorbed dose determination is shown.

Air↗
PubMed1997

Practical implementation of enhanced dynamic wedge in the CadPlan treatment planning system.

The Varian CadPlan algorithm for computation of relative dose distributions and monitor unit calculations for Enhanced Dynamic Wedge (EDW) fields is based on a combination of open field beam data and Segmented Treatment data Tables. Calculation of dose by the pencil beam convolution model uses scatter kernels and boundary kernels to create the distribution. The principles of the pencil beam convolution model is presented. Comparison of measured and calculated monitor units and relative dose distributions showed good agreement and the deviations are within international accepted tolerans. Test results indicate that the EDW model works satisfactorily for all energies and wedge angles.

Particle Accelerators↗
PubMed1996

Continuous beds for microchromatography: detection of proteins by a blotting membrane technique.

Continuous beds have been used as matrices for cation- and anion-exchange chromatography of proteins on columns with an i.d. in the range of 0.005-0.015 mm. On-tube uv detection is not feasible at low protein concentrations with these narrow-bore columns. Therefore, a more sensitive detection system has been developed based on blotting technique: as the protein zones leave the microcolumn chromatographically they become adsorbed onto a rotating polyvinylidene difluoride blotting membrane. The protein spots can then be visualized by means of Coomassie brilliant blue, immunomethods, and other standard techniques. By using an immunomethod 0.015 ng of human transferrin can easily be detected. The blotting membrane can be washed with water without loss of adsorbed protein. This is an attractive feature because the presence of salts, etc., diminishes the accuracy in the determination of molecular weights of proteins by mass spectrometry. The microcolumns are easy to prepare. A solution of appropriate monomers is sucked into a piece of fused silica tubing. The rod formed upon polymerization contains channels through which the eluent can pass. No supporting frit is required because the polymer rod is anchored by covalent bonds to the tubing wall.

Blotting, Western↗
PubMed1996

Capillary-zone electrophoresis in agarose gels using absorption imaging detection.

A simple home-built electrophoretic unit and a commercially available charge-coupled device (CCD) camera with image acquisition and analysis software were used to study the separation process in zone electrophoresis experiments in 4 cm long, round capillaries (inside diameter 0.2 mm). Several capillaries could be investigated simultaneously. The absorption imaging system was used not only to follow the course of the separation but also to study the interaction between biologically active substances (proteins, detergents, enzymes and-substrate). Since the system allows visual on-line observation of the separation one can rapidly decide when the analysis is finished, which often shortens the analysis time. The electrophoresis method presented is suitable also for preparative runs, since direct visualizations of a solute zone allows it to be excised and then used for further studies.

Electrophoresis, Agar Gel↗
PubMed1996

High-performance field inversion capillary electrophoresis of 0.1-23 kbp DNA fragments with low-gelling, replaceable agarose gels.

Field inversion capillary gel electrophoresis (FICGE) has been used for the separation of 0.1-23 kbp DNA fragments in a low-melting, low-gelling agarose gel. The influence of the amplitude of the voltage pulses, the pulse times and gel concentrations on the separation factor has been studied and found to be similar to that of polyacrylamide gels. Very high resolution can be obtained by altering continuously the pulse times and/or voltage according to a program tailor-made for the size of the DNA molecules to be separated (programmed FICGE). The advantage of these agarose gels in comparison with polyacrylamide gels is that they are nontoxic, easy to prepare and they have high UV transmission. They give a resolution that is equivalent to or better than that of polyacrylamide gels, and the risk of bubble formation in the gel is small. In addition, they are replaceable and, therefore, very convenient for automated analyses.

Automation↗
PubMed1995

Comparison in spontaneous ventilation of the Maxima with the Humphrey ADE breathing system and between four methods for detecting rebreathing.

An enclosed efferent, afferent reservoir breathing system (Maxima, Life Air Pty Ltd), being valveless, was compared to a simple afferent reservoir system (Humphrey ADE, A mode), having a valve, by assessing fresh gas flow (VF) requirements, with respect to ventilation (VE), that prevents rebreathing in volunteers, awake and breathing spontaneously. The results are recorded in terms of the quotient VF/VE associated with the onset of rebreathing. At the same time four clinical methods for assessing rebreathing were evaluated from the perspective of suitability for practical application during anaesthesia. No significant difference was found in the VF requirements between the ADE and Maxima breathing systems with respective values obtained for the quotient VF/VE of 0.80 and 0.77. Our findings showed that the method of sampling carbon dioxide (CO2) at the outflow of the efferent limb of the patient connector (eliminated CO2 method) in both afferent reservoir systems provided the highest flow rate and most reliable indication for detecting potential or actual rebreathing, when attempting to minimize VF. It provides no additional deadspace or resistance to gas flow, and has the advantage of being the only qualitative method that is reliable for the purpose of detecting the onset of rebreathing.

Airway Resistance↗
PubMed1993

Glial fibrillary acidic protein in the cerebrospinal fluid of children with autism and other neuropsychiatric disorders.

The cerebrospinal fluid (CSF) of 47 children and adolescents with autism was analyzed for the contents of two astroglial proteins, the glial fibrillary acidic protein (GFA) and S 100. The results were contrasted with those obtained in similarly aged cases with other neuropsychiatric disorders (n = 25) and in normal children (n = 10). S-100 did not discriminate the groups from each other. However, GFA in autism and autistic-like conditions was at a level almost three times that in the normal group. The results could implicate gliosis and unspecific brain damage in autism. An alternative model would be increased synapse turnover regardless of underlying cause.

Adolescent↗
PubMed1992

Preparative capillary electrophoresis based on adsorption of the solutes (proteins) onto a moving blotting membrane as they migrate out of the capillary.

A micropreparative capillary electrophoresis apparatus equipped with a new type of fraction collection device is described: solutes, such as proteins, are adsorbed onto a moving blotting membrane (for instance a polyvinylidene difluoride membrane) as they migrate electrophoretically out of the capillary. The adsorbed proteins are visualized by conventional protein staining methods or by fluorescent labeling. Specific identification of separated components by an immunological technique is demonstrated. The method also offers the potential to analyze proteins and peptides collected on the membrane by gas phase sequencing and mass spectrometry.

Adsorption↗
PubMed1992

Elevated CSF glutamate in Rett syndrome.

The concentration of free amino acids was measured in the cerebrospinal fluid of four patients with Rett syndrome. The reference material were patients with autistic disorder who had CSF aminoacid levels similar to those reported for healthy children. The concentration of glutamate-but of no other amino acid-was markedly elevated in the CSF of the RS patients. The results are discussed in the context of excitotoxicity in neurodegenerative disease.

Adult↗
PubMed1991

Can Cl- ions be extruded from a gamma-aminobutyric (GABA)-acceptive nerve cell via GABAA receptors on the plasma membrane cytoplasmic side?

1. In this commentary we discuss results obtained by a micromethod for the study of Cl- permeability across single nerve membranes from rabbit Deiters' neurons. 2. These results showed the presence of GABAA receptors on the nerve cell membrane cytoplasmic side. 3. We could show that these receptor complexes have a higher affinity for GABA than their extracellularly facing counterparts. Moreover, they present a phenomenon of desensitization. Another distinct property is that upon activation by GABA, they expose positive charges at their cytoplasmic mouths. 4. We propose that these receptor complexes could function in situ as a device for extruding Cl- anions from the nerve cell interior. This phenomenon would create an electrochemical gradient for Cl- penetration into the cell upon the action of extracellular GABA, after its presynaptic release.

Animals↗
PubMed1988

A microelectrophoretic method for the evaluation of GABA transaminase activity.

The reduction to the micro-scale of a recently described electrophoretic method for the evaluation of GABA catabolism by GABA-T is presented. The micromethod involves the electrophoresis, in 1 mm diam. capillaries, of small samples of mixtures of [14C]GABA and its metabolites. By coupling this procedure to previously devised micromethods, it was possible to evaluate GABA-T attack to 14C labeled GABA diffusing across a single microdissected neuronal membrane.

4-Aminobutyrate Transaminase↗
PubMed1988

"Intracellular" GABA affects the equilibrium distribution of Cl- across the plasma membrane of a GABA acceptive neuron.

The permeability of Cl- ions through single microdissected plasma membrane from Deiters' neurons was studied by a microtechnique. In particular, the time course of the passage of 36Cl- ions from a microchamber, M1, to another one, M2, across the membrane was followed. This study was performed with or without gamma-amino-butyric acid (GABA) in the two microchambers. The results suggest that in basal conditions the high intracellular concentration normally present in these neurons, 3.3 mM (1), causes a higher permeability of Cl- in the direction inside----outside in the respect of the plasma membrane. "Extracellular" GABA, 0.1 mM, is able to abolish this imbalance in Cl- permeability in the two opposite directions. This event appears to be the basis for GABA induced hyperpolarization of these neurons.

Animals↗
PubMed1987

Increase in chloride ion permeability across the nerve cell membrane after the endogenous antigen S-100 incorporation.

36Cl fluxes through microdissected Deiters' neuronal membranes have been studied in a microchamber device simulating the extra- and intracellular compartments. GABA stimulates Cl- permeability through the membranes by 24%. Also, S-100/Ca2+ incorporation into the Deiters' membrane increases 36Cl- permeation to a similar extent. The two effects do not appear to be additive. This circumstance is interpreted as indicating that S-100/Ca2+ exerts its effects via postsynaptic GABAA receptor complexes.

Animals↗