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Biomedical subjects

J S Hansen

Publications and source records attributed to J S Hansen.

At least 19 recordsLinked to original sources
PubMed2006

Microscopic simulations of an exothermic chemical wave front: departure from the continuity equations.

We perform microscopic simulations of a reactive dilute gas and study the propagation of an exothermic chemical wave front in an infinite, one-dimensional medium. The simulation results concerning front propagation speed and concentrations, temperature and stream velocity profiles are compared with the results of the integration of the macroscopic continuity equations in the case of fast reactions. The discrepancies between the two approaches are related to a chemically induced departure from local equilibrium.

Journal Article↗
PubMed2006

Molecular-dynamics simulations and master-equation description of a chemical wave front: effects of density and size of reaction zone on propagation speed.

We compare the master-equation description and molecular-dynamics simulations of a chemical wave front. We find that the front propagation speed depends on the number of particles in the reaction zone. For the master equation the dependence follows the well-known logarithmic prediction obtained when introducing a cutoff into the macroscopic reaction-diffusion equation. The molecular-dynamics simulations reveal that the logarithmic law is compromised for dense fluids.

Journal Article↗
PubMed2001

Adjuvant and immuno-suppressive effect of six monophthalates in a subcutaneous injection model with BALB/c mice.

The prevalence of allergic airway diseases is rapidly increasing in Western Europe and North America. This increase in disease prevalence may be associated with environmental pollutants. The present study investigated the adjuvant and immuno-suppressive effect of a series of monophthalates which are considered to be important metabolites of commonly used phthalate plasticizers. The effects were studied in a screening model. Ovalbumin (OA), used as the model antigen, was injected subcutaneously in the neck region of BALB/cJ mice with or without one of the test substances, mono-n-butyl phthalate (MnBP), monobenzyl phthalate (MBnP), mono-n-octyl phthalate (MnOP), mono-2-ethylhexyl phthalate (MEHP), mono-iso-nonyl phthalate (MiNP) or mono-iso-decyl phthalate (MiDP). The levels of OA-specific IgE, IgG1 and IgG2a in sera were measured by ELISA. Immuno-suppressive effect, defined as a statistically significant reduction in IgE or IgG1 antibody production, was observed with MEHP (1000 microg/ml, IgE and IgG1), MnOP (1000 microg/ml, IgE and IgG1), MiNP (1000 microg/ml, IgE and 10 microg/ml, IgG1) and MiDP (100 microg/ml, IgE and IgG1). Adjuvant effect, defined as a statistically significant increase in IgE or IgG1 antibody level, occurred with MEHP (10 microg/ml, IgE), MnOP (100 microg/ml, and 10 microg/ml, IgG1) and MiNP (100 microg/ml, IgE). No statistically significant immune modulating effect was seen with MBnP and MnBP.

Adjuvants, Immunologic↗
PubMed1996

Resistance to V3-directed neutralization caused by an N-linked oligosaccharide depends on the quaternary structure of the HIV-1 envelope oligomer.

A conserved N-glycan present within the V3 loop of gp120 modulates the sensitivity to neutralization by antibodies directed to the V3 loop. A glycan-deficient mutant of HIVLAI, designated HIVA308, displayed a 100-fold increase in sensitivity to neutralization by anti-V3 MAb NEA-9205 compared to wild-type HIVLAI. This difference in sensitivity was not caused by an alteration of the antibody binding site itself, as NEA-9205 had equal affinity for both wild-type and mutant monomeric gp120. In contrast, virion-associated wild-type gp120 was immunoprecipitated less efficiently with NEA-9205 than virion-associated mutant gp120. This difference was completely abrogated, if immunoprecipitation were carried out in the presence of detergent. Furthermore, treatment of virion preparations with detergent exposed the C-terminal D7324 epitope, which is inaccessible on virion-associated gp120 but readily accessible on monomeric, soluble gp120. Finally, both wild-type and mutant monomeric, soluble gp120 were precipitated equally efficiently by NEA-9205 in the absence of detergent. Thus, the NEA-9205 epitope was readily accessible on monomeric gp120 regardless of the presence of the 306N-glycan, and inaccessibility of the NEA-9205 epitope imparted by the 306N-glycan was observed only on the intact envelope oligomer.

Animals↗
PubMed1995

Measurement of wall deformation and flow limitation in a mechanical trachea.

A mechanical model of the human trachea is investigated experimentally. A modified version of an earlier model, it consists of a square sectioned rigid tube in which part of one wall is removed, and replaced by a prestretched flat latex membrane. Air is drawn from atmosphere through an inlet into the rigid upstream tube; it then flows through the flexible section and finally through a rigid section into a plenum chamber where suction is applied. As the membrane collapses in response to flow, the transmural pressure and deflection are measured at the mid-point. These values are used in conjunction with a finite deformation membrane wall theory to determine the elastic constant in a nonlinear material constitutive equation. This equation is used to predict the tube law. Results show that the flow limits at the long wave speed predicted by this law. Thus it behaves as a conventional collapsible tube while having the advantage of a rational wall model.

Airway Resistance↗
PubMed1991

Subcritical flutter in collapsible tube flow: a model of expiratory flow in the trachea.

Using an axisymmetric geometry that retains certain qualitative features of the trachea, we extend one-dimensional modeling of flow in collapsible tubes to include both curved shell effects and, for untethered tubes, wall inertia. A systematic scaling of the finite deformation membrane equations leads to an approximate set which is consistent with the one-dimensional fluid model; axial and normal wall variables are coupled elastically, but only axial inertia is retained. Transverse curvature causes elastic coupling that can give rise to axial wall motion and a flutter instability. The source of instability is the product of a nonzero reference axial curvature with axial tension variation due to axial stretching. The numerical results suggest that this mechanism may be significant even in processes which cannot be assumed one-dimensional.

Biomechanical Phenomena↗
PubMed1991

Effects of time and watershed characteristics on the concentration of Cryptosporidium oocysts in river water.

Water samples were collected from four locations on two rivers in Washington State and analyzed by membrane filtration-immunofluorescence assay to establish Cryptosporidium oocyst concentrations. Sampling locations were selected to evaluate effects of watershed character, from pristine mountain to downstream agricultural, on oocyst concentrations. Samples were collected at six biweekly intervals from late June to early September, with two additional sets of five samples taken on separate days (one set taken at bihourly intervals and one set taken simultaneously). Cryptosporidium oocysts were found in 34 of 35 samples at concentrations ranging from about 0.2 to 65 oocysts per liter. Oocyst concentrations were highest early in the sampling period, when they were influenced by postrainfall runoff, and decreased through the summer months. Oocyst concentrations found in ten samples collected on two days (5 samples per day) showed no short-term variations. Oocyst concentrations and oocyst production per square mile (ca. 2.6 km2) of watershed found in water draining a controlled public water supply watershed were the lowest observed. The concentrations and production rates for drainage from an adjacent, comparable, but uncontrolled watershed were nearly 10 times higher. The concentration and production rates of the downstream area influenced by dairy farming were nearly 10 times higher than rates at the upstream stations. The data showed clearly that oocyst concentrations were consistently observed above the detection limit of the analytical method, about 0.1 oocysts per liter; that oocyst concentrations were continuous as opposed to intermittent; and that watershed character and management affected surface water oocyst concentrations significantly.

Animals↗
PubMed1989

Physiological hypertrophy of the heart and atrial natriuretic peptide during rest and exercise.

The influence of physiological cardiac hypertrophy on the concentration of plasma atrial natriuretic peptide was studied in six male athletes and six normally active, matched control men. They were examined by echocardiography during a graded exercise test on a bicycle ergometer. Plasma atrial natriuretic peptide was measured at rest, at each workload until exhaustion, and 15 and 30 minutes after the exercise test. Echocardiography showed that the athletes had a significantly larger left atrium, left ventricular end diastolic diameter, left ventricular posterior wall, interventricular septum, left ventricular ejection fraction, and left ventricular mass than the controls. The athletes performed significantly more work than the control group--325 W v 277 W. The plasma concentration of atrial natriuretic peptide rose by a mean factor of 2.76 (range 1.78-4.28) in all men from rest to maximum exercise. There were no differences between the athletes and the controls in the concentrations of plasma atrial natriuretic peptide at rest, at any workload, or at maximum workload. Neither was there any difference in the increase in plasma atrial natriuretic peptide between the groups. There was no correlation between the plasma concentrations of atrial natriuretic peptide and any of the variables measured by echocardiography. In healthy young men plasma atrial natriuretic peptide rises by a factor of about 2.8 during maximum exercise and the size of the chambers on the left side of the heart or left ventricular hypertrophy does not seem to influence the concentration of plasma atrial natriuretic peptide at rest or during exercise.

Adult↗
PubMed1988

Practical limits on the biomagnetic inverse process determined from in vitro measurements in spherical conducting volumes.

A technique of locating current dipoles in spherical conducting volumes by determining the location of the magnetic field maximum and inverting the magnetic field equations was developed and the expected localisation errors were predicted. AC current dipoles were placed in spheres of uniform conductivity. Each dipole's magnetic field was measured and its location was calculated by determining the angle between the magnetic field null and maximum and using an iterative inverse solution to the magnetic field equations. Absolute agreement between predicted magnetic field strengths and actual magnetic field measurements was within 5%. A study of the effect of signal to noise ratio and number of data points in the analysis indicates that dipole localisation of approximately 1 mm is achievable for a signal to noise ratio greater than 10 decibels (S/N greater than 10 db).

Brain↗
PubMed1985

Interspecies conservation of retinal guanosine 5'-triphosphatase. Characterization by photoaffinity labelling and tryptic-peptide mapping.

Light-activated hydrolysis of cyclic GMP is achieved through the photoexcitation of rhodopsin, a process which then triggers the replacement of GDP for GTP by a retinal guanosine 5'-triphosphatase referred to as 'transducin'. The transducin-GTP complex then switches on the phosphodiesterase [Fung, Hurley & Stryer (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 152-156]. The bovine transducin consists of an alpha-subunit (39000 Mr), which is a GTP-binding component, together with a beta-(37000 Mr) and a gamma-subunit (10000 Mr). We have purified retinal transducin from cow, pig, chick and frog. The enzyme specific activities and sodium dodecyl sulphate/polyacrylamide-gel-electrophoretic profiles indicate that this enzyme is similar in all species except the frog. Whereas the bovine, pig and chick transducins consist of major 37000- and 39000-Mr components, that of the frog consists of a single 75000-Mr component. Labelling of the GTP-binding components with the photoaffinity label 8-azidoguanosine [gamma-32P]triphosphate demonstrated that the 37000-Mr components of the cow, pig and chick and the 75000-Mr component of the frog were major GTP-binding components. In addition, peptide maps of radioiodinated tryptic peptides indicate that the frog 75000-Mr protein is highly related to the pig transducin. These results demonstrate evolutionary conservation of retinal transducin and the presence of a higher-Mr, but nonetheless highly conserved form, of transducin in the frog. The relationship of this component to the recently reported rod-outer-segment inhibitor protein [Yamazaki, Stein, Chernoff & Bitensky (1983) J. Biol. Chem. 258, 8188-8194] is discussed.

Animals↗
PubMed1985

Characterization of polypeptides from human nuclear cataracts by Western blot analysis.

Water-soluble and water-insoluble polypeptides from nuclei of clear vs. opaque and brunescent human lenses were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretically transferred to nitrocellulose paper. Treatment of the nitrocellulose blots with monospecific antisera to human alpha and beta crystallin and to antisera against the Major Intrinsic Polypeptide (MIP26) of lens membrane demonstrated no difference in binding between microdissected sections of clear vs. opaque (and brunescent) nuclei. In contrast, treatment of nitrocellulose blots with monospecific antisera to human gamma crystallin demonstrated little or no binding to polypeptides from opaque (and brunescent) nuclei as compared with age-matched clear nuclei. These results demonstrate the selective involvement of gamma crystallins in opacification (and brunescence) in the human lens nucleus, and strongly suggest the presence of covalent changes of the gamma crystallin molecule during development of the human nuclear cataract.

Aged↗
PubMed1985

Antisera to synthetic peptides of lens MIP26K (major intrinsic polypeptide): characterization and use as site-specific probes of membrane changes in the aging human lens.

Based upon the amino acid sequence of bovine lens MIP26K obtained from cDNA cloning (Gorin, Yancey, Cline, Revel and Horwitz, 1984), two octapeptides (amino acid nos 252-259, 240-247) near the C-terminus have been synthesized. Rabbit antisera to these peptides recognize the intact MIP26K molecule from bovine, human and chick lens membrane. When compared with rabbit antisera to intact MIP26K or to its major cyanogen bromide fragment (CB-1), the antiserum to the sequence 252-259 was able to recognize age-related changes in human MIP26K not detectable by the conventional anti-MIP26K or anti-CB-1 sera.

Adult↗
PubMed1985

Partial characterization of three distinct populations of human gamma-crystallins.

Certain low molecular weight crystallins may be involved preferentially in the process of human cataractogenesis. Three distinct populations of monomeric crystallins with molecular weights ranging from 19,000 to 24,000 have been demonstrated previously by electrophoresis in the presence of sodium dodecyl sulfate (SDS). The authors now report the chromatographic separation of these three components from young human lenses. Each of the three species has unique profiles on isoelectric focusing and native polyacrylamide gels as well as on SDS gels. All three species show similar patterns of age-related modification in their charge characteristics. These three populations of polypeptides all appear to be gamma-crystallins. The relative amounts of the three vary with age, which accounts for the greater ease of their separation in extracts from young lenses as compared with adult lenses.

Aged↗
PubMed1984

High molecular weight aggregates from human cataracts: characterization by Western blot analysis.

The formation of covalently linked, high molecular weight protein aggregates has been thought to play an important role in opacification of the human lens. Antisera were used in Western blot analysis to demonstrate the involvement of all major classes of lens proteins (alpha, beta and gamma crystallin; the major intrinsic membrane polypeptide) in covalent aggregation. Of these classes, aggregation of gamma and beta crystallins via intermolecular disulfide bonding and aggregation of the major intrinsic membrane polypeptide via intermolecular, non-disulfide bonding were more pronounced in cataractous as compared with normal lenses.

Cataract↗
PubMed1983

Major intrinsic polypeptide of lens membrane. Biochemical and immunological characterization of the major cyanogen bromide fragment.

A protein of Mr 26000 has been shown to be the major component of eye-lens junctions, which are similar but not identical to the gap junctions of liver and other tissues. Cyanogen bromide cleavage of the Mr 26000 polypeptide from bovine lenses yields a major fragment of Mr 15000 (fragment 1). However, if the junctions are first treated with trypsin or carboxypeptidase Y, cyanogen bromide treatment yields a fragment of reduced molecular weight. Since protease treatment has been shown to cleave residues almost exclusively from the carboxy-terminal end of the Mr 26000 polypeptide, it follows that fragment 1 represents the carboxy-terminal half of this molecule, part of which is exposed to proteolytic attack outside the membrane. This latter result is corroborated by the fact that antisera which recognize both the Mr 26000 polypeptide and fragment 1 fail to do so after preadsorption with intact membranes. In addition, comparative amino acid and partial sequence analyses of the Mr 26000 polypeptide and fragment 1 indicate that fragment 1 is more hydrophilic in character, suggesting that much of the amino-terminal half of the Mr 26000 polypeptide is buried within the lipid bilayer.

Amino Acid Sequence↗
PubMed1983

Presence of low molecular weight polypeptides in human brunescent cataracts.

Microdissected sections from opaque & brunescent lens nuclei contain low molecular weight (4,000-8,000 dalton) polypeptides not found in microdissected sections of transparent lens nuclei. Tryptic digestion of these polypeptides from different cataracts reveal similar peptide maps. Together, these results support the involvement of proteolysis in human cataractogenesis, and suggest the possibility of similar molecular mechanisms occurring in cleavage of lens polypeptides during formation of the opaque & brunescent human cataract.

Aged↗