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In 2004, we collected 211 specimens of European field mice (genus Apodemus; subgenus Sylvaemus) from 16 localities in northern, western, central, and southern Ukraine, including the Crimean Peninsula. We used cytochrome-b mitochondrial DNA sequence data to investigate species diversity, distributional patterns, and taxonomy of Apodemus in Ukraine. Sequence data proved useful for species-level discrimination, because the 11 species examined were defined by low levels of intraspecific variation (mean range, 0.00‐3.35%) and by high levels of interspecific variation (mean range, 5.37‐18.9%). We identified the 211 specimens to 1 of 4 species: A. flavicollis (n ¼ 121), A. sylvaticus (n ¼ 34), A. uralensis (n ¼ 16), and A. witherbyi (n ¼ 40). Although all 4 species are known from Ukraine, this study provides new information about the ranges and population identity for these species in southeastern Europe. For example, our analyses substantiate the marked genetic structure reported for A. sylvaticus and document the presence of northern and southern continental lineages of this species in Ukraine that are hypothesized to have been isolated from each other in glacial refugia approximately 1.5 million years ago (.5% genetic divergence). Banks of the Dneiper River in northern Ukraine represent an area of secondary contact for the 2 lineages. Additionally, although application of A. witherbyi as a species-level name is debatable, examination of our genetic and morphological data supports its validity and priority over junior synonyms A. hermonensis and A. iconicus.

We discuss the history and prospects for the one-dimensional models of thermonuclear explosions in carbon-oxygen stellar cores. In connection with the recently studied SN 2002ic, which combines the properties of classical type Ia and IIn supernovae, we hope that our delayed detonation mechanism is applicable not only to binary, but also to single presupernovae. Since a large amount of 56Ni is synthesized, it can also describe adequately the light curves of supernovae similar to SN 2002ic.

While biological membrane fusion is classically defined as the leak-free merger of membranes and contents, leakage is a finding in both experimental and theoretical studies. The fusion stages, if any, that allow membrane permeation are uncharted. In this study we monitored membrane ionic permeability at early stages of fusion mediated by the fusogenic protein influenza hemagglutinin (HA). HAb2 cells, expressing HA on their plasma membrane, fused with human red blood cells, cultured liver cells PLC/PRF/5, or planar phospholipid bilayer membranes. With a probability that depended upon the target membrane, an increase of the electrical conductance of the fusing membranes (leakage) by up to several nS was generally detected. This leakage was recorded at the initial stages of fusion, when fusion pores formed. This leakage usually accompanied the “flickering” stage of the early fusion pore development. As the pore widened, the leakage reduced; concomitantly, the lipid exchange between the fusing membranes accelerated. We conclude that during fusion pore formation, HA locally and temporarily increases the permeability of fusing membranes. Subsequent rearrangement in the fusion complex leads to the resealing of the leaky membranes and enlargement of the pore.

Based on a one-dimensional hydrodynamic model, we investigate carbon burning in a thermonuclear type-Ia supernova in the approximation of unsteady convection. The relatively broad range of convective parameters, 1×10−3≤αc≤2×10−3, in which delayed detonation from the edge takes place was found to be preserved only for cases with a low boundary temperature at the presupernova stage, Tb(PS) = 6.4 × 106 K, and with a high envelope mass, mex ≃ 2 × 10−3M⊙. In cases with a more realistic temperature, Tb(PS) = 2 × 108 K, which corresponds to helium burning in the shell source, and with a lower mass mex, delayed detonation from the edge takes place only at αc = 2 × 10−3, while at αc = 1 × 10−3, numerous model pulsations occur during t≳500 s. Artificial viscosity is shown to give a determining contribution to the increase in entropy in outer model shells, which is caused by the generation of weak shock waves during pulsations. We also show that the entropies calculated by two independent methods are equal.

Blue light is the primary entrainment signal for a number of developmental and morphological processes in the lower eucaryote Neurospora crassa. Blue light regulates photoactivation of carotenoid synthesis, conidiation, phototropism of perithecia and circadian rhythms. Changes in the electrical properties of the plasma membrane are one of the fastest responses to blue light irradiation. To enable patch-clamp studies on light-induced ion channel activity, the wall-less slime mutant was used. Patch-clamp experiments were complemented by non-invasive ion-selective measurements of light-induced ion fluxes of slime cells using the vibrating probe technique. Blue light usually caused a decrease in conductance within 2-5 minutes at both negative and positive voltages, and a negative shift in the reversal potential in whole-cell patch-clamp measurements. Both K+ and Cl- channels contribute to the inward and outward currents, based on the effects of TEA (10 mM) and DIDS (500 microM). However, the negative shift in the reversal potential indicates that under blue light the Cl- conductance becomes dominant in the electrical properties of the slime cells due to a decrease of K+ conductance. The ion-selective probe revealed that blue light induced the following changes in the net ion fluxes within 5 minutes: 1) decrease in H+ influx; 2) increase in K+ efflux; and 3) increase in Cl- influx. Ca2+ flux was unchanged. Therefore, blue light regulates an ensemble of transport processes: H+, Cl-, and K+ transport.

The characteristics of elongation, branching, septation, and nuclear morphology in hyphal tips (of ~400 μm in length) of the mycelial fungus Neurospora crassa isolated from the mycelium and cultivated for several hours have been investigated using intracellular fluorescent markers. The newly formed branches had the following characteristic features: (1) the predefined orientation was conserved, whereas the diameter decreased (from 10–20 to 6.5 ± 0.4 μm), as did the elongation rate (from 24 ± 1 to 6.7 ± 0.5 μm/min); (2) a disturbed branching pattern with abnormally large internodal distances (up to 1471 μm) and developmental arrest of part of the buds of lateral branches; and (3) a conserved septation pattern and a relatively constant length of hyphal segments (68 ± 2 μm). The size of the nucleus-free zone at the tip (5–33 μm) and the distance between the first septum and the growth point (210 ± 15 μm) in the daughter branches of the isolated fragments were almost the same as in hyphae connected to the mycelium, whereas the average distance between the growth point and the first lateral branch (492 ± 127 μm) and the variability of this parameter were higher in the isolated fragments. The morphology of the nuclei and the size of the nucleus-free zone near the growth point did not differ from those reported for normal vegetative hyphae of N. crassa. The experimental model developed may be used for the elucidation of details of molecular genetic mechanisms that underlie the regulation of interactions between the intracellular structures that provide tip growth of the hyphae in N. crassa.

A model of a carbon-oxygen (C--O) presupernova core with an initial mass 1.33 M_\odot, an initial carbon mass fraction 0.27, and with an average mass growth-rate 5 x 10^{-7} M_\odot/yr due to accretion in a binary system was evolved from initial central density 10^9 g/cm^3, and temperature 2.05 x 10^8 K through convective core formation and its subsequent expansion to the carbon runaway at the center. The only thermonuclear reaction contained in the equations of evolution and runaway was the carbon burning reaction 12C + 12C with an energy release corresponding to the full transition of carbon and oxygen (with the same rate as carbon) into 56Ni. As a parameter we take \alpha_c - a ratio of a mixing length to the size of the convective zone. In spite of the crude assumptions, we obtained a pattern of the runaway acceptable for the supernova theory with the strong dependence of its duration on \alpha_c. In the variants with large enough values of \alpha_c=4.0 x 10^{-3} and 3.0 x 10^{-3} the fuel combustion occurred from the very beginning as a prompt detonation. In the range of 2.0 x 10^{-3} >= \alpha_c >= 3.0 x 10^{-4} the burning started as a deflagration with excitation of stellar pulsations with growing amplitude. Eventually, the detonation set in, which was activated near the surface layers of the presupernova (with m about 1.33 M_\odot) and penetrated into the star down to the deflagration front. Excitation of model pulsations and formation of a detonation front are described in detail for the variant with \alpha_c=1.0 x 10^{-3}.

When long-term bone marrow cultures are treated with Amphotericin B (AB) their haemopoietic stem cells (HSC) cease growing. This is not a toxic effect of the drug because once that is removed, HSC resume clonal growth and, given sufficient time, form as many cells as HSC in untreated cultures. Amphotericin B-evoked inhibition of blood formation is probably mediated by transmembrane communication between HSC and stroma for the following reasons: (1) AB does not stop HSC forming colony-forming units in culture (CFU-c) when HSC are separated from stroma by culturing them on Transwell inserts above the stroma. (2) Conditioned media (CM) from AB-containing or normal long-term cultures (LTC) does not inhibit normal marrow cells forming colonies in semi-solid cultures without stromal underlays. (3) AB itself does not stop bone marrow cells forming colonies in semi-solid cultures nor does it stop stromal cells growing or prejudice their long-term maintenance. (4) Furthermore, growing stromal cells with AB does not alter the number of transcripts they form for cytokines and chemokines to any large extent, including TGF-beta1. We have extensive, though circumstantial, evidence that gap junctions are involved in this communication. AB only stopped the growth of HSC when we blocked intercellular communication via gap junctions (GJIC) (tested by micro-injection of lucifer yellow). Lipophilic compounds that do not affect GJIC had no effect on the growth of HSC. Looking at a series of stromal cell lines from foetal liver and neonatal bone marrow we found that extensive GJIC correlated with stromal support of the late-appearing clones formed by primitive HSC (week 3-5 cobblestone-area forming cells, CAFC). We propose that the proliferation of HSC is regulated via transmembrane communication between stromal and HSC. Our findings support the proposal that gap junctions play a part in this stromal-dependent regulation.

Phagocytosis is an important cellular process that in multicellular organisms ensures a defence against microbial invasion and removal of effete/apoptotic cells. Phenomenologically, phagocytosis is a process of internalization or engulfment by a cell of particles of a certain size (more than 0.5 μm) (Ofek et al., 1995; Pratten & Lloyd, 1986; Koval et al., 1998; Aderem & Underhill, 1999; Morrissette et al., 1999; Tjelle et al., 2000; May & Machesky, 2001; Djaldetti et al., 2002). After the contact of a particle with a phagocytozing cell, named “phagocyte” in the 19th century (see Heifets, 1982; Gordon, 2008), plasma membrane underneath the particle forms either invagination or extensions (pseudopods) surrounding the particle and eventually forms a vesicle (phagosome) that delivers the particle inside the cell.

Cholesterol-Binding Peptides and Phagocytosis

We present calculations of the cooling evolutionary sequences of hot (T eff >12×10 3 K) white dwarf stars. The input physics is discussed in some detail, with special emphasis on the thermal conductivity and plasmon neutrino emission assumed. We suggest our own approximation for the latter. We find that the calculated effective temperature distribution of white dwarfs is rather sensitive to the assumed mass. The best fit to the observations yields the mass M=0.7 M ○. . With the inclusion of non-standard physics, we confirm the upper limit on the neutrino magnetic moment to be μ ν

The topology of the tight junction is probed by introducing dipicrylamine (dpa-), a lipid-soluble anion, into the membranes of hepatocyte pairs in culture. Once partitioned into the membrane, dpa- ions are free to move in the hydrophobic core of the membrane, where their mobile charges greatly increase membrane capacitance. If tight junctions are lines of membrane fusion, dpa- will cross the tight junction without traversing a polar headgroup layer. Furthermore, the electric potential across the tight junction will be equal to the difference in membrane potentials of the two cells. dpa- can therefore be expected to move electrophoretically from cell membrane to cell membrane across the junction in response to an intercellular voltage difference. Experiments performed under double whole-cell clamp show that this transfer occurs as follows: First, dpa- causes an intercellular current unrelated to gap junctions to flow in response to an intercellular voltage difference. Second, this electrophoretic removal or addition of dpa- from a cell's membrane through the tight junction must reduce or increase its dpa- content and thus its capacitance. Experiments confirm this prediction: We detect rapid, symmetric, and reversible changes in membrane capacitance in response to changes in the membrane potential of the neighboring cell. Finally, we find that hepatocyte membranes contain a negatively charged endogenous molecule that contain a negatively charged endogenous molecule that can move from cell to cell like dpa- under the influence of an intercellular potential difference. We conclude that membrane fusion occurs at tight junctions and that this hydrophobic intercellular pathway can play a role in intercellular communication.

Bank vole, Clethrionomys glareolus, specimens have been annually sampled from the radioactive Chernobyl, Ukraine, environment and nonradioactive reference sites since 1997. Exposed voles continually exhibit increased mitochondrial DNA hap-lotype (h) and nucleotide diversity (ND), observed in the hypervariable control region (1997–1999). Increased maternal mutation rates, source–sink relationships, or both are proposed as hypotheses for these differences. Samples from additional years (2000 and 2001) have been incorporated into this temporal study. To evaluate the hypothesis that an increased mutation rate is associated with increased h, DNA sequences were examined in a phylogenetic context for novel substitutions not observed in haplotypes from bank voles from outside Ukraine or in other species of Clethrionomys. Such novel substitutions might result from in situ mutation events and, if largely restricted to samples from radioactive environments, support an increased maternal mutation rate in these areas. The only unique substitution meeting this criterion was found in an uncontaminated reference site. All other substitutions are found in other haplotypes of the bank vole or in other species. Increased maternal mutation rates do not appear to explain trends in h and ND observed in northern Ukraine. Studies examining ecological dynamics will clarify the reasons behind, and significance of, increased levels of h in contaminated areas.

Not available

Low gadolinium concentrations induce rapid gigaseal formation and cell adhesion to glass and plastic (polystyrene) substrates in the slime mutant of Neurospora crassa. Cellular adhesion is independent of an integrin-mediated mechanism, because pretreatment with the oligopeptide ARG-GLY-ASP-SER (RGDS) did not inhibit it, and there was no spatial correlation between integrin and adhesions. In contrast, concanavalin A and beta-galactosidase both inhibit adhesion, suggesting that adhesion is mediated by sugar moeities at the cell surface. The adhesion sites are motile in the plasma membrane, as shown by the movement of polystyrene microspheres on the cell surface. In addition to an integrin-based adhesive system, which has already been characterized in walled hyphal cells, hyphae have evolved at least two different plasma membrane-based adhesion mechanisms. The relatively non-specific sugar-mediated adhesion caused by gadolinium may be part of the mechanism of gigaseal formation in other cells. In the absence of sugar-mediated adhesion, gadolinium increases the magnitude of the gigaseal in giant unilamellar liposomes composed of phosphatidylcholine, phosphatidylethanolamine, and cholesterol, with or without the negatively charged phosphatidylserine. Thus, gigaseal formation involves at least two different mechanisms.

Shape dynamics and permeability of a membrane neck connecting a vesicle and plasma membrane are considered. The neck is modeled by a lipid membrane tubule extended between two parallel axisymmetric rings. Within a range of lengths, defined by system geometry and mechanical properties of the membrane, the tubule has two stable shapes: catenoidal microtubule and cylindrical nanotubule. The permeabilities of these two shapes, measured as ionic conductivity of the tubule interior, differ by up to four orders of magnitude. Near the critical length the transitions between the shapes occur within less than a millisecond. Theoretical estimates show that the shape switching is controlled by a single parameter, the tubule length. Thus the tubule connection can operate as a conductivity microswitch, toggling the release of vesicle content in such cellular processes as “kiss-and-run” exocytosis. In support of this notion, bistable behavior of membrane connections between vesicles and the cell plasma membrane in macrophages is demonstrated.

Weak acids are efficient blockers of gap-junctional conductance. It is generally accepted that intracellular acidification produced by weak acids fully accounts for the gap-junctional uncoupling. Protonation of the cytoplasmic portions of the channel-forming protein connexin is thought to lead to the conformational changes switching the channel from the open into the closed state. If this is the only mechanism of the weak-acid induced uncoupling, then the correlation between junctional conductance (Gj) and intracellular pH (pHin) should not depend on the means of intracellular acidification. We compared the responses of junctional conductance in BHK cells measured in double whole-cell experiments to the applied transmembrane concentration gradients of bicarbonate or ammonium. These treatments were to lower pHin in a predictable way according to the equations: pHin = pHout -lg[[HCO3]out/HCO3-]in) or pHin = PHout - lg[[NH4+]in[NH4+out), respectively. We found that the behavior of Gj depended on the substance used. At a 500-fold bicarbonate gradient (calculated pHin approximately 4.8) the cells remained coupled, while a 100- or 10-fold gradient of ammonium imposing pHin approximately 6.1 produced fast uncoupling. The responses of junctional conductance were often accompanied or preceded by changes of non-junctional membrane conductance. We suggest that the mechanisms of the weak acid/base-induced channel gating may contain an additional "lipophilic" component due to the presence of the non-dissociated form of the acid/base in cell membrane.

Infection of cells with influenza virus is mediated by the virus envelope protein hemagglutinin (HA) which induces fusion of viral and target membranes. Earlier we showed using fluorescent microscopy that HAb2 cells expressing HA on their plasma membranes fused with PLC cells when pH of the external medium was decreased to -5. In the present work we used double whole-cell recording to monitor the intercellular conductance in HAb2/PLC cell pairs during fusion. In approximately 40% of cell pairs the pH drop induced the intercellular conductance, which we interpret as the formation of a fusion pore. The following stages of the conductance growth were distinguished: initial fluctuations near zero (flicker), a subsequent slow increase up to 1-4 nS and a final rapid increase up to 10-100 nS (complete fusion). The first detectable intercellular conductance change (opening of a fusion pore) was accompanied by an increase in the conductances of both HAb2 and PLC cell membrane. This observation suggests that the early pore complex should be leaky. The dynamics of the intercellular conductance appeared to depend upon the voltage difference between the fusing HAb2 and PLC cells: voltages higher than 40 mV facilitated the conductance growth.

Pain threshold sensitivity determination and recording of somatosensory evoked potentials in response to electrical skin stimulation were used to study the dynamics of pain sensitivity in medical students in mid-semester before blood donor and examination procedures and in the post-procedure period during performance of an editing test. Increases in pain sensitivity thresholds were seen in all subjects during the examination period and on performance of the editing test. Differences in changes in evoked potential amplitudes were found, depending on the individual-typological characteristics of the nervous system and the quality of motivationally determined states. Subjects with different individual-typological characteristics had different subjective pain sensation dynamics in test conditions.

Current views on the molecular mechanisms of the pH dependence of gap junctions are mainly based on the experimental fact that extracellularly applied CO2 or other weak acids rapidly and reversibly block junctional conductance and also decrease intracellular pH. Data are presented suggesting that the mechanism of the uncoupling action of weak acids may be restricted to intracellular acidification. Hypotheses concerning possible protonation sites in the connexin molecules are also considered.

Tight junctions (TJ) are specialized membrane structures found in cell-cell contact areas where the membranes of the neighbouring cells come into a close proximity. TJs have a characteristic ultrastructure on thin cross-section and freeze-fracture images and are regarded one of the diagnostic features of epithelial and endothelial cells where TJs form a transepithelial/transendothelial paracellular filter permeable for molecules of a certain size and also separate apical and basolateral domains of the plasma membrane of an epithelial cell. Two molecular models of TJs seek to explain structural and functional properties of TJs, a lipid model and a protein model. Due to the recent advances in biochemistry and molecular biology of TJs the protein model is most widely accepted. This review compares once again the ability of the two models to explain the phenomenology of TJs. The data on TJ ultrastructure and distribution are recalled here, including the data on TJs in fibroblastic cells where TJs appear fragmented or focal. TJ functions are considered, among which may be an intercellular communication due to cell-to-cell diffusion of lipophilic molecules. TJ modulators are listed and their activity in respect of the lipid phase transitions is noted. The major advantages and drawbacks of the two molecular models of TJs are discussed and a "synthetic" version of the lipid and protein models, reconciling the achievements of them both, is suggested.

Arachidonic acid (AA) is known to inhibit intercellular conductance in normal and tumour cells. We showed that junctional conductance (Gj) in isolated murine hepatocytes was relatively tolerant to the uncoupling effect of AA. Extracellular application of 100 microM AA decreased Gj in less than 50% of hepatocytes, and the effect was much slower in other cells (10-15 min vs. 2-5 min, respectively). The uncoupling effect of AA did not depend on the intracellular [Ca2+] within the pCa(i) range 7.7-9.0. Similar results were obtained using the pipette-filling solutions with low (1 mM) and high (10 mM) concentrations of a Ca-chelating agent (EGTA). To verify whether the resistance of the hepatocyte Gj to AA may result from the "wash-out" of the intracellular intermediates during the intracellular dialysis, Gj was measured 10-45 min after the preincubation of hepatocytes with AA. After such a treatment, in 62% of cell pairs the Gj values recorded did not differ from the control. Extracellular or intracellular acidification (pHo 6.0 or pHi 5.0-6.0) did not markedly affect the AA action. However, in some cases AA induced the recovery of Gj blocked after intracellular acidification, the phenomenon suggesting the activation of the H+ transport in the presence of AA. Possible mechanisms of the observed resistance of junctional conductance of mouse hepatocytes in primary culture are discussed.

We investigated the effect of arachidonic acid on the intercellular communication of a rat mammary tumor cell line. This polyunsaturated fatty acid reversibly reduced the intracellular pH and raised the concentration of cytoplasmic free Ca 2+ . However, neither low pH nor elevated [Ca 2+ ] j influenced gapjunctional coupling. Measurements with the double whole cell patch-clamp technique imply that arachidonic acid influences gap-junctional permeability via a direct lipid-protein interaction.

We give a complete review of various expansions which may be used for quick and accurate computing of the thermodynamic functions of an ideal Fermi gas. We begin with the well-known expression for the equation of state of an ultrarelativistic Fermi gas, which is in thermal equilibrium with blackbody radiation. This elementary expression is valid when the fermion mass is completely neglected in comparison to the average fermion kinetic energy. After that we show how to take into account the fermion mass; in other words, how to find an analytic form of the equation of state which is valid for a moderate degree of relativism of fermions. Contrary to the known expressions, the obtained expansion over the mass powers, as well as the elementary equation of state of an ultrarelativistic gas, holds for both a cold degenerate and a hot nondegenerate gas. Then we present expressions efficient in various ranges of temperature and density and derive some new approximations. The boundaries of applicability of all the expansions are specified on the temperature-density plane. {copyright} {ital 1996 The American Astronomical Society.}

Cell culture density is shown to alter the parameters characterizing phagocytic activity of cells in vitro. Phagocytosis index (PI, mean number of beads per cell in the bead-containing population) and phagocytosis percent (PP, percentage of bead-containing cells in cell population under study) for IC-21 macrophages incubated in the presence of non-opsonized 2-μm fluorescent latex beads were determined using fluorescent microscopy and ImageJ software specially adapted for the purpose. Under control conditions (DMEM without serum), increase in cell culture density was accompanied with a decrease of both parameters of the phagocytic activity. At a mean density of 4 cells/105 μm2 (9 cells per a viewfield) PI was 7.1 ± 0.2 beads/cell and at 20 cells/105 μm2 (40 cells per a viewfield) PI dropped to 4.6 ± 0.1 beads/cell. PP was less sensitive, varied in the range of 95–100% but also decreased as the cell density grew. At any density, PI was 1.5–2 times higher than the expected value (number of beads per µm2 × cell contour area); apparently this divergence can be accounted for by cell locomotion and capture of a larger number of beads than could drop onto a motionless cell with a constant contour area. Increase in cell density was also accompanied by a decrease of the cell contour area (Sc), which amounted to 750 ± 16 μm2 at a density of 4 cells/105 μm2 and 346 ± 4 μm2 at a density of 20 cells/105 μm2. As the bead concentration was the same in all experiments, density-dependent decrease in PI and PP may be related with the observed decrease in cell contour area. Yet, the bead number per cell area unit (PI/Sc) was bigger at higher density and PI/Sc was higher in cells with smaller Sc. Thus, individual (specific) activity of the cells did not lessen with an increase of the cell culture density in the range studied (4–20 cells/105 μm2). Reduction of the cell contour area may reflect alteration in cell adhesion to the substrate as well as competitive relations between adhesion and phagocytic processes. The data obtained imply that cell culture density has to be controlled as a factor notably altering the phagocytic activity parameters. The effects of serum, methyl-β-cyclodextrin, and carbenoxolon reported earlier [Golovkina et al. 2009. Biol membrany. 26 (5), 379–386] are re-evaluated and confirmed here.