Tracking S4 movement by gating pore currents in the bacterial sodium channel NaChBac

Voltage-gated sodium channels mediate the initiation and propagation of action potentials in excitable cells. Transmembrane segment S4 of voltage-gated sodium channels resides in a gating pore where it senses the membrane potential and controls channel gating. Substitution of individual S4 arginine gating charges (R1–R3) with smaller amino acids allows ionic currents to flow through the mutant gating pore, and these gating pore currents are pathogenic in some skeletal muscle periodic paralysis syndromes. The voltage dependence of gating pore currents provides information about the transmembrane position of the gating charges as S4 moves in response to membrane potential. Here we studied gating pore current in mutants of the homotetrameric bacterial sodium channel NaChBac in which individual arginine gating charges were replaced by cysteine. Gating pore current was observed for each mutant channel, but with different voltage-dependent properties. Mutating the first (R1C) or second (R2C) arginine to cysteine resulted in gating pore current at hyperpolarized membrane potentials, where the channels are in resting states, but not at depolarized potentials, where the channels are activated. Conversely, the R3C gating pore is closed at hyperpolarized membrane potentials and opens with channel activation. Negative conditioning pulses revealed time-dependent deactivation of the R3C gating pore at the most hyperpolarized potentials. Our results show sequential voltage dependence of activation of gating pore current from R1 to R3 and support stepwise outward movement of the substituted cysteines through the narrow portion of the gating pore that is sealed by the arginine side chains in the wild-type channel. This pattern of voltage dependence of gating pore current is consistent with a sliding movement of the S4 helix through the gating pore. Through comparison with high-resolution models of the voltage sensor of bacterial sodium channels, these results shed light on the structural basis for pathogenic gating pore currents in periodic paralysis syndromes.     

Modified Egyptian talc as internal sizing agent for papermaking

Mineral fillers have long been used in papermaking. The furnish of the writing and printing paper depends on using the fillers as internal or surface treatments. Talc, as an Egyptian filler material, was used as it is or after modification to be used as internal sizing for bleached rice straw pulp. Talc was modified chemically with phthalic anhydride and urea, as well as with using rosin size. Talc is chemically inert. The modification was carried out to change the nature of the native talc. The mechanical and optical properties for internal sizing papers were studied. The results indicated that modified talc with phthalic anhydride enhances the mechanical and optical properties for sized hand-sheets. It was clear that modification of the talc plays a role in improvement of the fiber–filler–fiber bond.     

Respiratory allergy to Blomia tropicalis: Immune response in four syngeneic mouse strains and assessment of a low allergen-dose,short-term experimental model

Background

The dust mite Blomia tropicalis is an important source of aeroallergens in tropical areas. Although a mouse model for B. tropicalis extract (BtE)-induced asthma has been described, no study comparing different mouse strains in this asthma model has been reported. The relevance and reproducibility of experimental animal models of allergy depends on the genetic background of the animal, the molecular composition of the allergen and the experimental protocol.

Objectives

This work had two objectives. The first was to study the anti-B. tropicalis allergic responses in different mouse strains using a short-term model of respiratory allergy to BtE. This study included the comparison of the allergic responses elicited by BtE with those elicited by ovalbumin in mice of the strain that responded better to BtE sensitization. The second objective was to investigate whether the best responder mouse strain could be used in an experimental model of allergy employing relatively low BtE doses.

Methods

Groups of mice of four different syngeneic strains were sensitized subcutaneously with 100 μg of BtE on days 0 and 7 and challenged four times intranasally, at days 8, 10, 12, and 14, with 10 μg of BtE. A/J mice, that were the best responders to BtE sensitization, were used to compare the B. tropicalis-specific asthma experimental model with the conventional experimental model of ovalbumin (OVA)-specific asthma. A/J mice were also sensitized with a lower dose of BtE.

Results

Mice of all strains had lung inflammatory-cell infiltration and increased levels of anti-BtE IgE antibodies, but these responses were significantly more intense in A/J mice than in CBA/J, BALB/c or C57BL/6J mice. Immunization of A/J mice with BtE induced a more intense airway eosinophil influx, higher levels of total IgE, similar airway hyperreactivity to methacholine but less intense mucous production, and lower levels of specific IgE, IgG1 and IgG2 antibodies than sensitization with OVA. Finally, immunization with a relatively low BtE dose (10 μg per subcutaneous injection per mouse) was able to sensitize A/J mice, which were the best responders to high-dose BtE immunization, for the development of allergy-associated immune and lung inflammatory responses.

Conclusions

The described short-term model of BtE-induced allergic lung disease is reproducible in different syngeneic mouse strains, and mice of the A/J strain was the most responsive to it. In addition, it was shown that OVA and BtE induce quantitatively different immune responses in A/J mice and that the experimental model can be set up with low amounts of BtE.     

Rats go genomic

A report on the meeting 'Rat Genomics and Models', Cold Spring Harbor, USA, 8-11 December 2005.     

Synthesis,DNA binding,fluorescence measurements and antiparasitic activity of DAPI related diamidines

A novel series of extended DAPI analogues were prepared by insertion of either a carbon–carbon triple bond (16a–d) or a phenyl group (21a,b and 24) at position-2. The new amidines were evaluated in vitro against both Trypanosoma brucei rhodesiense (T. b. r.) and Plasmodium falciparum (P. f.). Five compounds (16a, 16b, 16d, 21a, 21b) exhibited IC₅₀ values against T. b. r. of 9 nM or less which is two to nine folds more effective than DAPI. The same five compounds exhibited IC₅₀ values against P. f. of 5.9 nM or less which is comparable to that of DAPI. The fluorescence properties of these new molecules were recorded, however; they do not offer any advantage over those of DAPI.     

Antimicrobial,Antioxidant and Larvicidal Activities of Spherical Silver Nanoparticles Synthesized by Endophytic Streptomyces spp.

Biological Trace Element Research - In this study, metabolites involved in the free-biomass filtrates for three endophytic actinomycetes of Streptomyces capillispiralis Ca-1, Streptomyces...     

Tissue responses exhibited by Biomphalaria alexandrina snails from different Egyptian localities following Schistosoma mansoni exposure

Snails’ susceptibilities to infection with Schistosoma mansoni were determined through observation of infection rates, total cercarial production and tissue responses of the first generation (F1) of Biomphalaria alexandrina snails, originally collected from different Egyptian governorates (Giza, Fayoum, Kafr El-Sheikh, Ismailia and Damietta) and responses were compared between groups. The emergence of cercariae for a 3-month period and the calculation of survival and infection rates, in control (Schistosome Biological Supply Center; SBSC) and infected snails were evaluated. SBSC and Giza snails showed greater susceptibilities to infection and lower mortality rates. In addition, at 6 and 72 h post-exposure to miracidia all the snail groups showed no difference in the anatomical locations of sporocysts. The larvae were found in the head-foot, the mantle collar and the tentacles of the snails. Sporocysts showed normal development with low tissue reactions in SBSC and Giza snail groups infected with S. mansoni miracidia (SBSC). However, in Fayoum, Kafr El-Sheikh, Ismailia and Damietta snail groups, variable tissue responses were observed in which numerous hemocytes made direct contact with S. mansoni larvae forming capsules. The results suggested that, different responses of B. alexandrina snail’s hemocytes towards S. mansoni are related to the degree of susceptibility of these snails. So this is important in planning the strategy of schistosomiasis control.     

Requirements for Arabidopsis ATARP2 and ATARP3 during epidermal development

Plant cells employ the actin cytoskeleton to stably position organelles, as tracks for long distance transport, and to reorganize the cytoplasm in response to developmental and environmental cues. While diverse classes of actin binding proteins have been implicated in growth control, the mechanisms of cytoskeletal reorganization and the cellular functions of specific actin filament arrays are unclear. Arabidopsis trichome morphogenesis includes distinct requirements for the microtubule and actin filament cytoskeletons. It also is a genetically tractable process that is providing new knowledge about cytoskeleton function in plants. The "distorted group" of mutants defines a class of at least eight genes that are required during the actin-dependent phase of trichome growth. Using map-based cloning and a candidate gene approach, we identified mutations in ARP3 (ATARP3) and ARP2 (ATARP2) genes as the cause of the distorted1 (dis1) and wurm (wrm) phenotypes, respectively. ARP2 and ARP3 are components of the evolutionarily conserved ARP2/3 complex that nucleates actin filament polymerization [3]. Mutations in DIS1 and WRM caused severe trichome growth defects but had relatively mild effects on shoot development. DIS1 rescued the phenotype of Deltaarp3 when overexpressed in S. cerevisiae. Developing dis1 trichomes had defects in cytoplasmic actin bundle organization and reduced relative amounts of cytoplasmic actin filaments in developing branches.     

Synthesis, anti-inflammatory activity and ulcerogenic liability of novel nitric oxide donating/chalcone hybrids

A group of novel nitric oxide (NO) donating chalcone derivatives was prepared by binding various amino chalcones with different NO donating moieties including; nitrate ester, oximes and furoxans. Most of the prepared compounds showed significant anti-inflammatory activity using carrageenan-induced rat paw edema method compared with indomethacin. The prepared compounds exhibited more protection than indomethacin in regard to gastric toxicity. Histopathological investigation confirmed the beneficial effects of the NO releasing compounds in reducing ulcer formation. The incorporation of the NO-donating group into the parent chalcone derivatives caused a moderate increase in the anti-inflammatory activity with a marked decrease in gastric ulcerations compared to their parent chalcone derivatives.     

The relationship between genetic variability and the susceptibility of Biomphalaria alexandrina snails to Schistosoma mansoni infection

In the present study, Biomphalaria snails collected from five Egyptian governorates (Giza, Fayoum, Kafr El-Sheikh, Ismailia and Damietta), as well as reference control Biomphalaria alexandrina snails from the Schistosome Biological Supply Center (SBSC) (Theodor Bilharz Research Institute, Egypt), were subjected to species-specific polymerase chain reaction (PCR) assays to identify the collected species. All of the collected snails were found to be B. alexandrina and there was no evidence of the presence of Biomphalaria glabrata. Randomly amplified polymorphic DNA (RAPD)-PCR assays showed different fingerprints with varying numbers of bands for the first generation (F?) of B. alexandrina snail populations (SBSC, Giza, Fayoum, Kafr El-Sheikh, Ismailia and Damietta). The primer OPA-1 produced the highest level of polymorphism and amplified the greatest number of specific bands. The estimated similarity coefficients among the B. alexandrina populations based on the RAPD-PCR profiles ranged from 0.56 (between SBSC and Ismailia snails) to 0.72 (between Ismailia and Kafr El-Sheikh snails). Experimental infection of the F? of progeny from the collected snails with Schistosoma mansoni (SBSC strain) showed variable susceptibility rates ranging from 15% in the Fayoum snail group to 50.3% in SBSC snails. A negative correlation was observed between the infection rates in the different snail groups and the distances separating their corresponding governorates from the parasite source. The infection rates of the snail groups and their similarity coefficients with SBSC B. alexandrina snails were positively correlated. The variations in the rates of infection of different B. alexandrina groups with S. mansoni, as well as the differences in the similarity coefficients among these snails, are dependent not only on the geographical distribution of the snails and the parasite, but also on the genetic variability of the snails. Introduction of this variability into endemic areas may reduce the ability of the parasite to infect local hosts and consequently reduce schistosomiasis epidemiology.