Showing papers by "Jagiellonian University published in 1998"

Asymmetric Dimethylarginine (ADMA): A Novel Risk Factor for Endothelial Dysfunction Its Role in Hypercholesterolemia

Abstract: Background—Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide (NO) synthase. Because endothelial NO elaboration is impaired in hypercholesterolemia, we investigated whether plasma concentrations of ADMA are elevated in young, clinically asymptomatic hypercholesterolemic adults. We further studied whether such elevation of ADMA levels was correlated with impaired endothelium-dependent, NO-mediated vasodilation and urinary nitrate excretion. In a randomized, double-blind, placebo-controlled study, we investigated whether these changes could be reversed with exogenous l-arginine. Methods and Results—We measured plasma levels of l-arginine, ADMA, and symmetrical dimethylarginine (SDMA) by high-performance liquid chromatography in 49 hypercholesterolemic (HC) and 31 normocholesterolemic (NC) humans. In 8 HC subjects, endothelium-dependent forearm vasodilation was assessed before and after an intravenous infusion of l-arginine or placebo and compared with 8 NC control subj...

Strengthening of horizontal cortical connections following skill learning

Abstract: Learning a new motor skill requires an alteration in the spatiotemporal pattern of muscle activation. Motor areas of cerebral neocortex are thought to be involved in this type of learning, possibly by functional reorganization of cortical connections. Here we show that skill learning is accompanied by changes in the strength of connections within adult rat primary motor cortex (M1). Rats were trained for three or five days in a skilled reaching task with one forelimb, after which slices of motor cortex were examined to determine the effect of training on the strength of horizontal intracortical connections in layer II/III. The amplitude of field potentials in the forelimb region contralateral to the trained limb was significantly increased relative to the opposite 'untrained' hemisphere. No differences were seen in the hindlimb region. Moreover, the amount of long-term potentiation (LTP) that could be induced in trained M1 was less than in controls, suggesting that the effect of training was at least partly due to LTP-like mechanisms. These data represent the first direct evidence that plasticity of intracortical connections is associated with learning a new motor skill.

Broad-band X-ray/γ-ray spectra and binary parameters of GX 339–4 and their astrophysical implications

Abstract: We present X-ray/γ-ray spectra of the binary GX 339–4 observed in the hard state simultaneously by Ginga and CGRO OSSE during an outburst in 1991 September. The Ginga X-ray spectra are well represented by a power law with a photon spectral index of Γ ≃ 1.75 and a Compton reflection component with a fluorescent Fe Kα line corresponding to a solid angle of an optically thick, ionized medium of ∼ 0.4 × 2 π. The OSSE data (≥ 50 keV) require a sharp high-energy cut-off in the power-law spectrum. The broad-band spectra are very well modelled by repeated Compton scattering in a thermal plasma with an optical depth of τ ∼ 1 and kT ≃ 50 keV. We also study the distance to the system and find it to be ≳ 3 kpc, ruling out earlier determinations of ∼ 1 kpc. Using this limit, the observed reddening and the orbital period, we find the allowed range of the mass of the primary is consistent with it being a black hole. We find the data are inconsistent with models of either homogenous or patchy coronae above the surface of an accretion disc. Rather, they are consistent with the presence of an inner hot disc with the viscosity parameter of α ∼ 1 accreting at a rate close to the maximum set by advection. The hot disc is surrounded by a cold outer disc, which gives rise to the reflection component and a soft X-ray excess, also present in the data. The seed photons for Comptonization are unlikely to be due to thermal synchrotron radiation. Rather, they are supplied by the outer cold disc and/or cold clouds within the hot disc. e± pair production is negligible if electrons are thermal. The hot disc model, for which scaled parameters are independent of the black hole mass, is supported by the similarity of the spectrum of GX 339–4 to those of other black hole binaries and Seyfert 1s. On the other hand, their spectra in the soft γ-ray regime are significantly harder than those of weakly magnetized neutron stars. Based on this difference, we propose that the presence of broad-band spectra corresponding to thermal Comptonization with kT ≳ 50 keV represents a black hole signature.

A spectral decomposition of the variable optical, ultraviolet and X-ray continuum of NGC 5548

Abstract: We present an analysis and decomposition of the broad-band optical/UV/X-ray/γ-ray spectrum of the Seyfert 1 galaxy NGC 5548. The spectrum consists of an average of simultaneous optical/IUE/Ginga observations accompanied by ROSATCGRO/OSSE data from non-simultaneous observations. We show that the overall optical/UV/X-ray/γ-ray spectrum can be deconvolved into three basic continuum components: a cool multitemperature blackbody, a hard thermal Comptonized component and an EUV/soft X-ray component well described by a thermal Comptonization continuum. Assuming that the optical/IUE spectrum comes from a cold disc, the maximum disc temperature is very well constrained by the data to be kTdisc = 3.2+0.2−0.2 eV. This rules out models explaining the soft excess as a far tail of the disc spectrum. We show that the soft excess inferred by the data requires a separate continuum component, which is consistent with thermal Comptonization in optically thick (τ ∼ 30), warm (∼0.3 keV) plasma. This Comptonization component contains a significant fraction of the source energy. The plasma parameters of the hard continuum (τ ∼ 2, kTHC ∼ 50 keV) are consistent with those suggested for the average spectrum of Seyferts. On the basis of the broad-band spectral model, we also re-analyse the simultaneous IUE/Ginga campaign. We find that the fluxes in all three continuum components are positively correlated. The total flux emitted in the hard component is positively correlated with both the spectral index and the solid angle of cold matter seen by the hot source. Such a correlation suggests that the variability mechanism is related to changes in the geometry of the continuum-emitting regions, and an excess in the amount of reflection requires deviations from a simple plane disc picture. The variations in the hard spectral index can then be explained by increased cooling of the hot plasma caused by the increased number of seed photons. We suggest that the geometry variations may be related to a transition region between a cold and a hot disc.

Induced thermotolerance and associated expression of the heat‐shock protein Hsp70 in adult Drosophila melanogaster

Abstract: 1. Inducible heat-shock proteins are synthesized when temperatures are increased to levels substantially above normal. The functional role of these proteins is well known at the cellular level. Today increasing interest has been directed towards the importance of heat-shock proteins for resistance of whole organisms to high-temperature stress and other environmental stressors. 2. Here the functional relationship between the heat-shock protein, Hsp70, and thermal resistance in adult Drosophila melanogaster was examined by comparing thermal resistance, i.e. survival at 39 °C for 85 min, and levels of Hsp70 at various times elapsed (2, 4, 8, 16, 32 and 64 h) after thermotolerance was induced by short-term acclimation/heat hardening at 37 °C for 55 min. 3. Levels of Hsp70 in both males and females were highest 2 h after heat hardening and declined with longer times elapsed. The rate of decrease initially was very fast but diminished with increasing time. After 32 h the level of Hsp70 approached the level in flies that were not hardened. Levels of Hsp70 in males exceeded that of females during the entire period. 4. Survival of both sexes increased with increasing time after heat hardening and reached an optimum between 8 and 32 h. Thereafter resistance decreased with longer times elapsed. Survival of females generally exceeded that of males except after 16 and 64 h. 5. Regression analysis applied to the data on Hsp70 levels revealed that the model describing these data could not explain the data for survival. Also, higher levels of Hsp70 in males compared with females were not associated with greater survival in males. However, statistical analysis on paired measurements of Hsp70 and survival revealed a positive association between Hsp70 level and survival at each time elapsed after induction of thermotolerance.

Trust, Distrust and Two Paradoxes of Democracy

Abstract: The measure of trust that people vest in their fellow citizens or institutions depends on three factors: the `reflected trustworthiness' of the target as estimated by themselves in a more or less rational manner, the attitude of `basic trustfulness' deriving from socialization, and the `culture of trust' pervading their society and normatively encouraging the trusting orientation. The author presents a model of a structural context conducive for the emergence of the culture of trust, and then argues that democratic organization contributes to trust-generating conditions, such as normative certainty, transparency, stability, and accountability. This influence is found to be doubly paradoxical. First, democracy breeds the culture of trust by institutionalizing distrust at many levels of democratic organization. And second, the strongest influence of democracy on the culture of trust may be expected when the institutionalized distrust remains a resource used sparingly and only when there appear significant b...

Regulation of ATP supply during muscle contraction: theoretical studies.

Abstract: The dynamic computer model of oxidative phosphorylation developed previously and successfully tested for large-scale changes in fluxes and metabolite concentrations was used to study the question of how the rate of ATP production by oxidative phosphorylation is adjusted to meet the energy demand during muscle contraction, which causes a great increase in ATP consumption in relation to the resting state. The changes in the respiration rate and ATP/ADP ratio after the onset of maximal work measured experimentally were compared with simulated changes in the respiration rate and ATP/ADP in several different cases, assuming direct activation of different steps by an external effector. On the basis of the computer simulations performed, it was possible to conclude which enzymes/metabolic blocks should be directly activated to cause the experimentally observable changes in fluxes and metabolite concentrations. The theoretical results obtained suggest that the parallel direct activation of actinomyosin-ATP-ase and oxidative phosphorylation by an external effector (for example calcium ions) is the main mechanism responsible for fitting of ATP production to ATP consumption, while the negative feedback via an increase in ADP concentration (decrease in ATP/ADP), which indirectly activates the ATP supply, plays only a minor role. Additionally, the conclusion is drawn that most of the oxidative phosphorylation steps should be directly activated in order to explain the observed changes in the respiration rate and ATP/ADP ratio (and also in other parameters) during muscle contraction. It is suggested that there should exist a universal external activator/regulatory mechanism which causes a parallel stimulation of different enzymes/processes. A possible nature of such an activator is shortly discussed.

Composed ensembles of random unitary matrices

Abstract: Composed ensembles of random unitary matrices are defined via products of matrices, each pertaining to a given canonical circular ensemble of Dyson. We investigate statistical properties of spectra of some composed ensembles and demonstrate their physical relevance. We also discuss the methods of generating random matrices distributed according to invariant Haar measure on the orthogonal and unitary group.

Comprehensive analysis of intermolecular charge-transfer excited states in C 60 and C 70 films

Abstract: We have investigated intermolecular charge transfer (CT) excited states and demonstrated their contribution to the excitation-relaxation and photocarrier generation mechanisms for both ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ polycrystalline films. This has been done (1) experimentally, using UV-visible absorption (Abs) and electroabsorption (EA), luminescence and its modulation by external electric-field and steady-state photoconductivity; (2) semiempirically, analyzing the Abs and EA spectra in order to determine the CT state energies and to estimate the variation of the average polarizability tensor and the dipole moment; and (3) theoretically, by performing calculations of polarization energies and electrostatic stabilization energies. The most significant CT states have been identified at approximately 2.43 and 3.50 eV for ${\mathrm{C}}_{60}$ films and at 2.26 and 3.60 eV for ${\mathrm{C}}_{70}$ films (data from the semiempirical analysis). Their properties have been discussed in terms of crystallographic and electronic structure, with special emphasis on their mixing with Frenkel states.

Habitat preference in the bombina hybrid zone in croatia.

Abstract: This paper demonstrates the effect of habitat heterogeneity and a habitat preference on the genetic structure of a hybrid zone between the toads Bombina bombina and B. variegata (Anura: Discoglossidae); 1613 toads from 85 sites across a transect near Pescenica, Croatia, were scored for five unlinked diagnostic allozyme markers. These were found to be largely concordant. Aside from minor systematic deviations, there was little variance in allele frequency among loci within sites. Yet the allele frequencies did not follow a smooth cline, but formed a mosaic in the center, such that neighboring sites could differ markedly in their enzyme score. A detailed ecological survey revealed a correlation between this pattern and habitat. In keeping with the typical breeding sites of the parental taxa, B. bombina-like hybrids were found more often in ponds, whereas B. variegata-like hybrids were more common in puddles. In addition, there was significant heterozygote deficit (FIS) and strong linkage disequilibrium (R), both of which were stronger on the B. bombina side of the transect, and stronger in puddles than ponds. Mark-recapture data showed: (1) that the animals disperse beyond the scale of the habitat pattern; (2) frequent turn-over of individuals within sites; and (3) nonrandom movement between two sites of different habitat type. We conclude that an active habitat preference must contribute to the observed association between marker alleles and habitat. As a consequence, there is incomplete mixing of the two gene pools, which could explain the high level of FIS and R. The asymmetry in these parameters may reflect asymmetry in the preference or in the distribution of habitats across the zone. We discuss the implications of habitat preference for the dynamics of hybrid zones.

Homology computation by reduction of chain complexes

Abstract: A new algorithm for computing the homology module of a finitely generated chain complex is given. It is based on local one-step reductions of the size of the initial chain complex and it has a clear geometrical interpretation. The complexity of the algorithm is discussed in special cases.

Electronic Properties of NiS2-xSex Single Crystals: From Magnetic Mott−Hubbard Insulators to Normal Metals

Abstract: The NiS{sub 2{minus}x}Se{sub x} system represents one of the best examples of a Mott-Hubbard system, i.e., a system in which, under appropriate conditions of concentration, temperature, or pressure, a metal-insulator transition driven by electron-electron interaction takes place. Here, the metallic phase is either antiferromagnetic (for 0.44 {le} x {le} 1) or paramagnetic (for x {ge} 1), whereas the insulating phase is as a rule antiferromagnetic (including the spin-canted phases). In this paper the authors review both the physical properties and outline the basic features of the theoretical approach to those correlated electron systems. Emphasis is placed on a qualitative understanding of the observed transformation of the system from semiconductor (or magnetic insulator) to metal.

Self‐assembly of Congo Red—A theoretical and experimental approach to identify its supramolecular organization in water and salt solutions

Abstract: The supramolecular organization of Congo Red molecules was studied to approach an understanding of the unusual complexation characteristics associated with the liquid crystalline nature of this dye. Differential scanning calorimetry (DSC) and nmr data indicate that Congo Red assembly arrangements differ in water and salt solutions. Compact, highly ordered material with a distinct melting transition is created, but not below 0.3% sodium chloride concentration. The twist in the assembly arrangement of Congo Red molecules, caused in water by repulsion, decreases when the charges are shielded, allowing for more overlapping of the naphthalene rings and their engagement in stacking interaction. The crystallization transition observed in DSC analysis of Congo Red fast-assembled by cooling in salt solutions indicates that the formation of compact crystalline mesophase material is a time-consuming process in which coplanarity and a highly ordered organization must be achieved. Two different superposition variants, called “direct” and “reversed” here, were considered fundamental to compact Congo Red organization. They correspond to optimal face-to-face ring stackings, and are formed by simple direct translation or alternative imposition of reversed (180° rotated) molecules, respectively. In NaCl solution (2.8%) there is a significant downfield chemical shift alteration of the nmr signal related to proton 8, which is in the naphthalene ring on the side opposite to the charged sulfonic group. It was associated selectively with the transition of Congo Red to compact form. This effect confirms the close approach of the sulfonic groups and proton 8, and indicates that formation of the reversed arrangement is favored in the Congo Red supramolecular organization. Molecular dynamics simulation based on AMBER 4.1 force field and analysis of electrostatic field densities around the molecule were used for comparative modeling. Molecular dynamics (150 ps) were simulated for two eight-molecule micelle models constructed to reflect direct and reversed arrangements of Congo Red molecules. Although both versions generally preserved their initial assembly structure in the simulations, the reversed version proved more stable. The proximity of the sulfonic group and proton 8, confirmed by computer analysis, explains the correlation between the formation of Congo Red micellar organization and the distinct shift alteration related to this proton, as found by nmr. © 1998 John Wiley & Sons, Inc. Biopoly 46: 267–281, 1998