Biomedical subjects

H U Keller

Publications and source records attributed to H U Keller.

At least 19 recordsLinked to original sources

PubMed2005

Rain, winds and haze during the Huygens probe's descent to Titan's surface.

The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent.

Atmosphere↗

PubMed2003

Chemotactically-induced redistribution of CD43 as related to polarity and locomotion of human polymorphonuclear leucocytes.

Leukocyte motility involves pseudopods extension at the leading edge and uropod contraction at the cell rear. Previous studies have shown that the glycoprotein CD43 redistributes to the uropod, when the cells develop polarity and locomotion. The present study addresses the question whether the accumulation of specific membrane molecules, such as CD43 at the contracted uropod precedes or follows development of polarity and locomotion. PMNs were labeled with fluorescent anti-CD43 antibodies and guided to polarize in the direction of a chemoattractant-containing micropipette or, once polarized, they were forced to reverse polarity and movement direction by placing the micropipette behind the uropod. This chemotactically-induced reversal of polarity was used as an efficient tool to analyse the sequence of events. CD43, but not another abundant surface glycoprotein CD45, was concentrated at the uropod. This documents that CD43 redistribution is a selective phenomenon. During reversal of polarity and of locomotion direction, the geometric center of the cell clearly changed direction earlier than the center of anti-CD43 fluorescence intensity. Thus, CD43 redistribution to the new uropod follows rather than precedes reversal of polarity, suggesting that CD43 redistribution is a consequence rather than a prerequisite for polarity and locomotion. PMNs making a U-turn maintained the pre-existing polarity and CD43 remained concentrated at the uropod, even when the front was moving in the opposite direction. Our data show that anterior pseudopod formation, rather than capping of CD43 at the uropod or the position of the uropod determines the direction of locomotion.

Antibodies, Monoclonal↗

PubMed2002

Phenotype modulation in non-adherent and adherent sublines of Walker carcinosarcoma cells: the role of cell-substratum contacts and microtubules in controlling cell shape, locomotion and cytoskeletal structure.

We characterised two sublines of Walker carcinosarcoma cells generated by epigenetic changes. Subline 1 cells were mostly polarised and made no or only non-adhesive cell-substratum contacts. Subline 2 cells were spread, adhesive and mainly non-polar. Subline 1 cells migrate in a non-adhesive mode which is very efficient but operates only in a 3D environment, whereas subline 2 cells migrate in an adhesive mode, which is less efficient but works on 2D and 3D substrata. Nocodazole had little or no effect on shape, polarity and locomotion of subline 1 cells. In glass-adherent subline 2 cells, 10(-6)M nocodazole increased the proportion of polarised cells migrating in an adhesive mode and decreased adhesion to the substratum, whereas 10(-5)M nocodazole further reduced the contacts and the cells reverted to a non-adhesive mode of locomotion. When non-polar subline 2 cells were detached mechanically or by nocodazole, they became polarised and morphologically indistinguishable from non-adherent subline 1 cells. On more adhesive plastic substrata, subline 2 cells produced heterogeneous responses to nocodazole including loss of polarity. The phenotypes of Walker carcinosarcoma sublines have similarities with a broad range of cell types ranging from leucocytes to fibroblast-like cells, suggesting that these phenotypic differences can be controlled by the adhesive and contractile state rather than the cell type. Adhesion modulates contractility (isometric or isotonic contraction) and vice versa and this determines morphology (shape, F-actin, myosin and alpha-actinin), locomotion and responses to microtubule-disassembly. The model may be applied to analyse the mechanisms controlling the phenotype of cells in general.

Actinin↗

PubMed2000

Protein kinase C isoforms involved in regulation of cell shape and locomotion of human fibrosarcoma HT1080 cells.

The role of protein kinase C (PKC) isoforms in the regulation of cell shape [switch between fibroblast-like and crescent shape (CS)] and of locomotion of human fibrosarcoma HT1080 cells has been investigated. The PKC activator phorbol myristate acetate (PMA) induced the transition of elongated fibroblast-like cells into CS cells and stimulated locomotion. Both responses to PMA were inhibited by the PKC inhibitor Ro 31-8220. Analysis of the time course showed that stimulation of shape changes (formation of CS cells) and locomotor activity (increase in the proportion and speed of locomoting cells) was maximal in the early phase of the response (up to 2.5 hr) and significantly decreased later (15 to 21 hr). CS formation and stimulated locomotion correlated closely with a marked redistribution from the cytosol to the membrane of PKC isoforms alpha, beta1 and gamma in the early phase (0.5 to 2 hr) following activation with PMA. The subsequent reduction of the proportion of CS cells and of cell locomotion correlated with down-regulation of these isoforms in the second phase (16 to 21 hr). In contrast, the total amount and distribution of PKC beta2 remained almost unchanged with 10(-8) M PMA up to 21 hr. Furthermore, changes in shape and locomotion did not correlate with the responses of PKC delta to PMA. Inhibition of PMA-stimulated locomotion by the more specific inhibitor Gö 6976 is consistent with a role of PKC alpha and beta1 in this response. Ro 31-8220 alone induced a moderate down-regulation of PKC isoforms alpha and delta, but it also inhibited the more pronounced down-regulation of these isoforms by PMA. Our results indicate that activation of PKC isoforms alpha, gamma and beta1, but not beta2 or delta, stimulates locomotion and formation of CS cells in human fibrosarcoma HT1080 cells.

Carbazoles↗

PubMed2000

Growth and form of planetary seedlings: results from a microgravity aggregation experiment.

The outcome of the first stage of planetary formation, which is characterized by ballistic agglomeration of preplanetary dust grains due to Brownian motion in the free molecular flow regime of the solar nebula, is still somewhat speculative. We performed a microgravity experiment flown onboard the space shuttle in which we simulated, for the first time, the onset of free preplanetary dust accumulation and revealed the structures and growth rates of the first dust agglomerates in the young solar system. We find that a thermally aggregating swarm of dust particles evolves very rapidly and forms unexpected open-structured agglomerates.

Models, Theoretical↗

PubMed2000

Redundancy of lamellipodia in locomoting Walker carcinosarcoma cells.

Locomoting metazoan cells usually form lamellipodia at the leading front and it is widely accepted that lamellipodia are required for locomotion. In this case, suppression of lamellipodia must stop locomotion. However, the experiments show that lamellipodia are redundant for locomotion of Walker carcinosarcoma cells. Low latrunculin A concentrations (10(-7) M) transform polarised locomoting cells with lamellipodia into cells without morphologically recognisable protrusions showing an increased speed of locomotion and a reduced amount of cellular F-actin. Whereas untreated cells show a fairly linear distribution of F-actin along the plasma membrane, cells lacking morphologically recognizable protrusions at the front show modifications at the front consisting in an irregular distribution of F-actin with formation of small or large patches of F-actin alternating with small or large gaps in the F-actin layer. This is associated with a reduced resistance to deformation pressure at the front of the cell. High concentrations of latrunculin A (>10(-7) M) compromising contraction at the rear stop locomotion, suggesting that cortical contraction is important for locomotion to occur in these cells. The results are consistent with the view that actin polymerization is important for formation of lamellipodia but they are not compatible with the view that lamellipodia are essential for locomotion of Walker carcinosarcoma cells. A unifying hypothesis for the formation of different types of protrusions is proposed.

Actins↗

PubMed2000

Effects of the myosin inhibitor 2,3-butanedione monoxime (BDM) on cell shape, locomotion and fluid pinocytosis in human polymorphonuclear leucocytes.

We investigated the role of myosin in polymorphonuclear leucocyte (PMN) shape changes, locomotion, and fluid pinocytosis using the myosin inhibitor 2,3 butanedione monoxime (BDM). Treatment of resting spherical PMNs with BDM produced spheroid cells showing small continuous shape changes (IC(50)=15.5 m m BDM) and occasionally small blebs. Cell polarity, as induced by the chemotactic peptide fNLPNTL or by colchicine, and locomotion were completely suppressed (IC(50)=8.4 to 10 m m). Suppression of fNLPNTL- or colchicine-induced cell polarity produced spheroid cells, suppression of PMA-induced shape changes and fluid pinocytosis produced non-motile spherical cells (IC(50)=25 to 30 m m BDM). BDM suppressed formation of lamellipodia but not formation of blebs. Suppression of microvilli by BDM as observed in resting spherical cells was partially antagonized by PMA. The results suggest that myosin is involved in stabilizing the shape of resting spherical cells, including microvilli, and that myosin is required for cell polarity, locomotion, fluid pinocytosis and for formation of lamellipodia, but not for formation of blebs.

Cell Size↗

PubMed1999

Redistribution of surface-bound con A is quantitatively related to the movement of cells developing polarity.

Capping in cells developing polarity has been reinterpreted on the basis of a quantitative analysis of Concanavalin A (Con A) redistribution and cell movement in Walker carcinosarcoma cells. Several new features emerged. Based on the developing asymmetry in the distribution of surface-bound Con A, the direction of cell movement and the prospective front-tail polarity can already be predicted when the cell is spherical. Development of polarity by an initially spherical cell is associated with formation of two parts. The concentrically contracting part (prospective uropod) characterized by surface-associated Con A decreases in size, while the other part is cleared from Con A and grows into formerly unoccupied space. Surface-bound Con A shows isotropic centripetal movement towards the initial position of the centroid of the spherical cell rather than rearward movement. Therefore, the centroid of fluorescence intensity remains either stationary or moves marginally forward with respect to the initial position of the spherical cell. The amount and direction of cell movement measured correlates closely with values predicted by a theoretical model that assumes a unidirectional transfer of volume from a stationary contracting compartment into a protruding compartment. The results suggest that isotropic (cortical) contraction of the initially spherical cells and one-sided relaxation rather than unidirectional retrograde movement of ligand-receptor complexes produces movement in cells developing polarity. Reversible accumulation of surface-bound Con A at the uropod occurring to a similar extent in untreated and colchicine-treated cells is partly due to membrane folding and partly to movement in the plane of the membrane.

Animals↗

PubMed1999

Beagle 2: a proposed exobiology lander for ESA's 2003 Mars Express mission.

The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies.

Equipment Design↗

PubMed1997

Results from the Mars Pathfinder camera.

Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity approximately 0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.

Atmosphere↗

PubMed1997

The spectrum of comet Hale-Bopp (C/1995 O1) observed with the Infrared Space Observatory at 2.9 astronomical units from the sun.

Comet Hale-Bopp (C/1995 O1) was observed at wavelengths from 2.4 to 195 micrometers with the Infrared Space Observatory when the comet was about 2.9 astronomical units (AU) from the sun. The main observed volatiles that sublimated from the nucleus ices were water, carbon monoxide, and carbon dioxide in a ratio (by number) of 10:6:2. These species are also the main observed constituents of ices in dense interstellar molecular clouds; this observation strengthens the links between cometary and interstellar material. Several broad emission features observed in the 7- to 45-micrometer region suggest the presence of silicates, particularly magnesium-rich crystalline olivine. These features are similar to those observed in the dust envelopes of Vega-type stars.

Carbon Dioxide↗

PubMed1997

Suppression of bleb formation, locomotion, and polarity of Walker carcinosarcoma cells by hypertonic media correlates with cell volume reduction but not with changes in the F-actin content.

The putative role of cellular or solvent volume in protrusive activity and locomotion has been investigated in blebbing Walker carcinosarcoma cells using hypertonic media. Blebbing, locomotion, and cell polarity are completely suppressed by 0.2 M sorbitol. The response occurs in two steps. In a first step, i.e. within 10 sec after the addition of sorbitol, blebbing and locomotion are inhibited and this is associated with an average cell volume reduction by 17% (corresponding to a reduction in solvent volume by 38%). It clearly precedes suppression of cell polarity (pre-existing protrusions, tail) occurring in a second step within 5 to 10 min after addition of sorbitol without additional reduction in the cell or solvent volume. The relative amount of F-actin does not correlate with the decrease in cell volume, suppression of blebbing, locomotion, and cell polarity. A significant decrease in the relative amount of F-actin is found only at volume reductions which are higher than those required to completely suppress blebbing, locomotion, and cell polarity. F-actin staining occurs preferentially along the cell membrane in isotonic as well as in hypertonic media. The results are best compatible with the hypothesis that hydrostatic pressure rather than actin polymerization at the front is the direct force driving the membrane forward during bleb formation. Cells with lamellipodia show a similar response to hypertonic media, suggesting that basically similar mechanisms may operate in both forms of protrusions.

Actins↗

PubMed1996

Protrusive activity quantitatively determines the rate and direction of cell locomotion.

Locomoting blebbing cells have been used as a model to obtain novel insight into the mechanisms of cell locomotion. We tested the hypothesis that locomotion can be due to progressive one-sided protrusion of cellular volume into pseudopods. The hypothesis is supported by the finding that the rate and direction of locomotion of individual Walker carcinosarcoma cells can be predicted by sequential measurement of protrusive activity. Protrusive activity at the front is closely associated with forward movement of the rear part of the cell. During bleb formation the cell membrane of Walker carcinosarcoma cells is pushed forward faster (1.2-4.1 microns/sec) than known rates of actin elongation.

Animals↗

PubMed1995

Selective responses (actin polymerization, shape changes, locomotion, pinocytosis) to the PKC inhibitor Ro 31-8220 suggest that PKC discriminately regulates functions of human blood lymphocytes.

The results suggest that protein kinase C (PKC) plays a pivotal role in the control of F-actin levels, locomotion, pinocytosis, and cell shape in lymphocytes. The PKC inhibitor Ro 31-8220 elicits a high proportion of polarized (ED50 = 1.5 x 10(-6) M) and locomoting cells and reduces the relative amount of F-actin (by 29% at 10(-5) M) in initially resting cells. Phorbol myristate acetate (PMA) counterbalances the polarizing effect of Ro 31-8220. This indicates that the spherical shape and the F-actin content of resting cells are maintained by constitutive PKC activity. PMA-induced increases in fluid pinocytosis, F-actin content, and formation of nonpolar cells with surface protrusion are suppressed by Ro 31-8220 (IC50 = 2-4 x 10(-7) M). Spherical cells and, at higher concentrations (ED50 = 3.3 x 10(-6) M), polarized cells are formed instead. As a result, lymphocyte function switches from fluid pinocytosis to cell polarity and locomotion. The data indicate that PKC is instrumental in selectively switching lymphocyte function between resting state, locomotor activity, and fluid pinocytosis. Ro 31-8220 is extremely potent in stimulating lymphocyte polarity and locomotion (B and T cells). It acts faster and/or produces a higher proportion of polarized lymphocytes than other available agonists. It may thus be used as a tool in further experiments requiring locomoting lymphocytes.

Actins↗

PubMed1995

Relationship between light scattering in flow cytometry and changes in shape, volume, and actin polymerization in human polymorphonuclear leukocytes.

Using two different cytometers, an Epics Profile II and a FACScan, we determined the extent to which changes in forward and right angle scatter are a reliable measure for changes in polymorphonuclear leukocyte (PMN) shape, volume, and actin polymerization and whether distinct types of shape changes in PMNs can be recognized. PMN stimulation can substantially change the positions of PMNs in the scatter diagram of the FACScan but not of the Epics Profile II. Within the limits of the experiments, it has been possible to determine whether or not a shape change has taken place using the FACScan but not using the Epics Profile II. However, using either cytometer, it has not been possible to determine which type of shape change (e.g., spherical vs. polarized vs. nonpolar cells) has taken place. Furthermore, forward or right angle scatter changes are not a reliable measure for changes in cell volume or actin polymerization of human PMNs.

Actin Cytoskeleton↗

PubMed1994

Selective effects of the PKC inhibitors Ro 31-8220 and CGP 41,251 on PMN locomotion, cell polarity, and pinocytosis.

Using two newly synthesized inhibitors, Ro 31-8220 and CGP 41,251, of protein kinase C (PKC), we analysed: (1) how distinct PMN functions (shape changes, locomotion, pinocytosis) are regulated, and (2) the role of protein phosphorylation and PKC in this process. We were able to transform: (1) resting PMNs into locomoting cells using fNLPNTL, (2) locomoting cells into non-locomoting highly pinocytic cells using PMA, and (3) PMA-stimulated cells showing marked pinocytosis into locomoting or into resting cells using Ro 31-8220. It is thus possible to selectively manipulate PMN function (resting state, locomotion, marked pinocytosis), indicating that there are different regulatory pathways. It was not possible to induce locomotion and marked pinocytosis simultaneously, indicating crosstalk between pathways. Ro 31-8220 inhibited PMA-induced shape changes (nonpolar cells) and pinocytosis, but not fNLPNTL-induced shape changes (polarity) and pinocytosis. At higher concentrations, Ro 31-8220 alone elicited cell polarity and chemokinesis, indicating that a constitutively active protein kinase is involved in maintaining the spherical shape of resting PMNs. Functional effects of another PKC inhibitor, CGP 41,251, on neutrophil function were strikingly different. CGP 41,251 selectively inhibited fNLPNTL-induced polarity and locomotion (but not colchicine or Ro 31-8220-induced polarity), and it failed to inhibit PMA-induced, stimulated pinocytosis and shape changes. Although the effects of Ro 31-8220 vs. CGP 41,251 on PMN function were strikingly different, the inhibition of profiles for constitutive and for fNLPNTL- or PMA-induced protein phosphorylation in intact PMNs showed only small differences, which could not yet be conclusively related to cell function.

Alkaloids↗

PubMed1993

The PKC-inhibitor Ro 31-8220 selectively suppresses PMA- and diacylglycerol-induced fluid pinocytosis and actin polymerization in PMNs.

The PKC-inhibitor Ro 31-8220 inhibits stimulated fluid pinocytosis of human PMNs induced by the PKC-activators phorbol myristate acetate (PMA, IC50 = 1.35 x 10(-6) M) or diacylglycerols (OAG, diC8) by 95%, whereas Ro 31-8220 has no effect on D2O- or fNLPNTL-induced pinocytosis and enhances cytochalasin D- induced pinocytosis. Also formation of F-actin induced by PMA or diacylglycerols is selectively inhibited. The results indicate that a Ro 31-8220 -sensitive PKC is involved in signal transduction for enhanced pinocytosis and F-actin formation in response to one class of stimuli (classical activators of PKC) but not to others.

Actins↗

PubMed1993

Colchicine-induced stimulation of PMN motility related to cytoskeletal changes in actin, alpha-actinin, and myosin.

Colchicine-induced stimulation of polymorphonuclear leukocyte (PMN) locomotion is an interesting model because extension of blebs at the front occurs at a rate (about 2.4 microns/s) which is far above that reported for growth of actin filaments. The following cytoskeletal changes were observed in colchicine-treated PMNs: (1) a small increase in cytoskeleton-associated actin was noted, as well as a somewhat more pronounced increase in cytoskeleton-associated alpha-actinin, as compared with untreated or DMSO-treated controls. There was, however, no measurable increase in F-actin as determined by NBD-phallacidin binding; (2) the values for the ratio (alpha-actinin/actin) are lower in PMNs treated with colchicine for 30 min, as compared with PMNs stimulated with fNLPNTL for 1 minute (non-polar ruffling cells) or 30 min (polarized locomoting cells); thus, this ratio may depend on the type of PMN motility; (3) in polarized PMNs F-actin was mainly located linearly all along the cell membrane; there was more intense staining at the front of the cells; (4) alpha-actinin appeared to colocalize with F-actin at the leading front, but not with F-actin at the tail of polarized cells; (5) myosin was preferentially found at the rear part of polarized cells but not or only to a small extent at the front. Our data indicate a close functional correlation between microtubules and microfilaments. We speculate that F-actin in combination with alpha-actinin promotes expansion of pseudopods, whereas myosin combined with F-actin promotes contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Actinin↗