AICAR prevents heat-induced sudden death in RyR1 mutant mice independent of AMPK activation

Mice with a knock-in mutation (Y524S) in the type I ryanodine receptor (Ryr1), a mutation analogous to the Y522S mutation that is associated with malignant hyperthermia in humans, die when exposed to short periods of temperature elevation (≥37 °C). We show here that treatment with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) prevents this heat-induced sudden death in this mouse model. The protection by AICAR is independent of AMP-activated protein kinase (AMPK) activation and results from a newly identified action of the compound on mutant Ryr1 to reduce Ca(2+) leak from the sarcoplasmic reticulum to the sarcoplasm. AICAR thus prevents Ca(2+)-dependent increases in the amount of both reactive oxygen species (ROS) and reactive nitrogen species (RNS) that act to further increase resting Ca(2+) concentrations. If unchecked, the temperature-driven increases in resting Ca(2+) concentrations and the amounts of ROS and RNS create an amplifying cycle that ultimately triggers sustained muscle contractions, rhabdomyolysis and death. Although antioxidants are effective in reducing this cycle in vitro, only AICAR prevents heat-induced death in vivo. Our findings suggest that AICAR is probably effective in prophylactic treatment of humans with enhanced susceptibility to exercise- and/or heat-induced sudden death associated with RYR1 mutations.     

<Emphasis Type="Italic">Pichia stipitis</Emphasis> xylose reductase helps detoxifying lignocellulosic hydrolysate by reducing 5-hydroxymethyl-furfural (HMF)

Background  

Pichia stipitis xylose reductase (Ps-XR) has been used to design Saccharomyces cerevisiae strains that are able to ferment xylose. One example is the industrial S. cerevisiae xylose-consuming strain TMB3400, which was constructed by expression of P. stipitis xylose reductase and xylitol dehydrogenase and overexpression of endogenous xylulose kinase in the industrial S. cerevisiae strain USM21.     

The factor stabilizing the bioluminescence of PVA-immobilized photobacteria

Immobilization of photobacteria in the cryogel of polyvinyl alcohol (PVA) was carried out. Immobilization was found to result in increased intensity and stability of bioluminescence. The elements determining the stability of bioluminescence were investigated. Selection of the strain was found to be of the highest importance. Among immobilized cells, Photobacterium phosphoreum exhibited the most intense and prolonged light emission, while Vibrio harveyi showed the least one. The technological procedures for cryogenic immobilization of photobacteria were determined. The role of the environment of gel formation in the preservation of the bioluminescence activity was determined. In the gels formed in rich medium for submerged cultivation of photobacteria, almost 100% luminescence activity was preserved, while light emission was considerably prolonged. Bioluminescence intensity of the preparations was shown to depend significantly on pH of the incubation medium. The pH shift to acidic values during prolonged incubation of immobilized cells was shown to be one of the factors of bioluminescence quenching. The stress effects of cryogenic immobilization were found to have an insignificant effect on the temperature profile of bioluminescence. Decreased reduction rate of the luciferase flavin substrate was shown to be a possible reason for bioluminescence quenching.     

Characteristics of the development of Eimeria species from gerbils in secondary hosts

Peculiarities of endogenous and exogenous developmental stages of the life cycle of Eimeria salasuzica Musajev et Vejsov, 1960, a parasite of Persian jird, and E. akeriana Ismailov et Gaibova, 1983, a parasite of Meriones blackleri, in two first recognized secondary hosts (Meriones vinogradovi and M. lybicus) were studied. The paper gives comparative data on the duration of infection, endogenous stages of development and variability of oocysts of the studied species of Eimeria obtained from the main and secondary hosts.     

Reduced natural selection associated with low recombination in Drosophila melanogaster

Synonymous codons are not used equally in many organisms, and the extent of codon bias varies among loci. Earlier studies have suggested that more highly expressed loci in Drosophila melanogaster are more biased, consistent with findings from several prokaryotes and unicellular eukaryotes that codon bias is partly due to natural selection for translational efficiency. We link this model of varying selection intensity to the population-genetics prediction that the effectiveness of natural selection is decreased under reduced recombination. In analyses of 385 D. melanogaster loci, we find that codon bias is reduced in regions of low recombination (i.e., near centromeres and telomeres and on the fourth chromosome). The effect does not appear to be a linear function of recombination rate; rather, it seems limited to regions with the very lowest levels of recombination. The large majority of the genome apparently experiences recombination at a sufficiently high rate for effective natural selection against suboptimal codons. These findings support models of the Hill-Robertson effect and genetic hitchhiking and are largely consistent with multiple reports of low levels of DNA sequence variation in regions of low recombination.      

Kappa-chain constant-region gene sequences in genus Rattus: coding regions are diverging more rapidly than noncoding regions

We have determined the nucleotide sequence of a 1,200-base pair (bp) genomic fragment that includes the kappa-chain constant-region gene (C kappa) from two species of native Australian rodents, Rattus leucopus cooktownensis and Rattus colletti. Comparison of these sequences with each other and with other rodent C kappa genes shows three surprising features. First, the coding regions are diverging at a rate severalfold higher than that of the nearby noncoding regions. Second, replacement changes within the coding region are accumulating at a rate at least as great as that of silent changes. Third, most of the amino acid replacements are localized in one region of the C kappa domain--namely, the carboxy-terminal "bends" in the alpha-carbon backbone. These three features have previously been described from comparisons of the two allelic forms of C kappa genes in R. norvegicus. These data imply the existence of considerable evolutionary constraints on the noncoding regions (based on as yet undetermined functions) or powerful positive selection to diversify a portion of the constant-region domain (whose physiological significance is not known). These surprising features of C kappa evolution appear to be characteristic only of closely related C kappa genes, since comparison of rodent with human sequences shows the expected greater conservation of coding regions, as well as a predominance of silent nucleotide substitutions within the coding regions.      

Inhibitory Effects of Phenolic Ecotoxicants on Photobacteria at Various pH Values

Kinetic characteristics of light emission by intact cells of photobacteria Photobacterium phosphoreum and Vibrio harveyi were studied (at pH 5.5, 7.0, and 8.0), as well as inhibitory effects of 2,4-di- and 2,4,5-triphenoxyacetic acids (2,4-D and 2,4,5-T), pentachlorophenol (PCP), and 2,6-dimethylphenol (2,6-DMP) (at the same pH values). The emission kinetics lacked a steady state, irrespective of pH. At pH 5.5, luminescence decayed exponentially in the 60-s range; at pH 7.0 and 8.0, a 5-min luminescence activation was observed. The respiratory activity of the cells decreased by more than an order of magnitude at pH 5.5 (compared to the levels observed at pH 7.0 and 8.0). The inhibitory effects of 2,4-D, 2,4,5-T, and PCP differed by one to two orders of magnitude, depending on pH. Maximum cell sensitivity to these compounds appeared at pH 5.5; minimum sensitivity, at pH 8.0. The effect of 2,6-DMP was pH-independent. The inhibitory effect was determined by the hydrophobicity of the molecule and pK values of the toxicants. At all pH values, substrate-depleted cells of photobacteria were more sensitive to chlorophenolic compounds than cells supplied with energy.     

Quantification of the virus-host interaction in human T lymphotropic virus I infection

Background

Cellular infection with human immunodeficiency virus (HIV) both in vitro and in vivo requires a member of the chemokine receptor family to act as a co-receptor for viral entry. However, it is presently unclear to what extent the interaction of HIV proteins with chemokine receptors generates intracellular signals that are important for productive infection.

Results

In this study we have used a recently described family of chemokine inhibitors, termed BSCIs, which specifically block chemokine-induced chemotaxis without affecting chemokine ligands binding to their receptors. The BSCI termed Peptide 3 strongly inhibited CCR5 mediated HIV infection of THP-1 cells (83 ± 7% inhibition assayed by immunofluoresence staining), but had no effect on gp120 binding to CCR5. Peptide 3 did not affect CXCR4-dependent infection of Jurkat T cells.

Conclusion

These observations suggest that, in some cases, intracellular signals generated by the chemokine coreceptor may be required for a productive HIV infection.     

Mechanosensitivity of an epithelial Na+ channel in planar lipid bilayers: release from Ca2+ block.

A family of novel epithelial Na+ channels (ENaCs) have recently been cloned from several different tissues. Three homologous subunits (alpha, beta, gamma-ENaCs) from the core conductive unit of Na(+)-selective, amiloride-sensitive channels that are found in epithelia. We here report the results of a study assessing the regulation of alpha,beta,gamma-rENaC by Ca2+ in planar lipid bilayers. Buffering of the bilayer bathing solutions to [Ca2+] < 1 nM increased single-channel open probability by fivefold. Further investigation of this phenomenon revealed that Ca2+ ions produced a voltage-dependent block, affecting open probability but not the unitary conductance of ENaC. Imposing a hydrostatic pressure gradient across bilayers containing alpha,beta,gamma-rENaC markedly reduced the sensitivity of these channels to inhibition by [Ca2+]. Conversely, in the nominal absence of Ca2+, the channels lost their sensitivity to mechanical stimulation. These results suggest that the previously observed mechanical activation of ENaCs reflects a release of the channels from block by Ca2+.