Low Cation Concentrations Research Articles

TRPM7 is a molecular substrate of ATP-evoked P2X7-like currents in tumor cells.

Within the ion channel-coupled purine receptor (P2X) family, P2X7 has gained particular interest because of its role in immune responses and in the growth control of several malignancies. Typical hallmarks of P2X7 are nonselective and noninactivating cation currents that are elicited by high concentrations (0.1-10 mM) of extracellular ATP. Here, we observe spurious ATP-induced currents in HEK293 cells that neither express P2X7 nor display ATP-induced Ca(2+) influx or Yo-Pro-1 uptake. Although the biophysical properties of these ionic currents resemble those of P2X7 in terms of their reversal potential close to 0 mV, nonrectifying current-voltage relationship, current run-up during repeated ATP application, and augmentation in bath solutions containing low divalent cation (DIC) concentrations, they are poorly inhibited by established P2X7 antagonists. Because high ATP concentrations reduce the availability of DICs, these findings prompted us to ask whether other channel entities may become activated by our experimental regimen. Indeed, a bath solution with no added DICs yields similar currents and also a rapidly inactivating Na(+)-selective conductance. We provide evidence that TRPM7 and ASIC1a (acid-sensing ion channel type Ia)-like channels account for these noninactivating and phasic current components, respectively. Furthermore, we find ATP-induced currents in rat C6 glioma cells, which lack functional P2X receptors but express TRPM7. Thus, the observation of an atypical P2X7-like conductance may be caused by the activation of TRPM7 by ATP, which scavenges free DICs and thereby releases TRPM7 from permeation block. Because TRPM7 has a critical role in controlling the intracellular Mg(2+) homeostasis and regulating tumor growth, these data imply that the proposed role of P2X7 in C6 glioma cell proliferation deserves reevaluation.

Quadruplex Turncoats: Cation-Dependent Folding and Stability of Quadruplex-DNA Double Switches.

Quadruplex (G4) nucleic acids, a family of secondary structures formed by guanine-rich sequences, exhibit an important structural polymorphism. We demonstrate here that G-rich DNA sequences may function as a double switch based on different triggers, provided that their quadruplex structures and stability display a high dependence on cation nature and concentration. A first switch is based on a remarkable antiparallel-to-parallel conversion, taking place in a few seconds at room temperature by addition of low KCl amounts to a sodium-rich sample. The second switch involves the conversion of alternative antiparallel quadruplex structures binding only one cation, formed in the presence of sub-millimolar potassium or strontium concentrations, to parallel structures by increasing the cation concentration. Incidentally, extremely low K(+) or Sr(2+) concentrations (≤5 equiv) are sufficient to induce G4 formation in a buffer devoid of other G4-promoting cations, and we suggest that the alternative structures observed contain only two tetrads. Such DNA systems are biological relevant targets, can be used in nanotechnology applications, and are valuable methodological tools for understanding DNA quadruplex folding, notably at low cation concentrations. We demonstrate that this behavior is not restricted to a narrow set of sequences but can also be found for other G-quadruplex-forming motifs, arguing for widespread applications.

Evaluation of stem rot in 339 Bornean tree species: implications of size, taxonomy, and soil-related variation for aboveground biomass estimates

Abstract. Fungal decay of heart wood creates hollows and areas of reduced wood density within the stems of living trees known as stem rot. Although stem rot is acknowledged as a source of error in forest aboveground biomass (AGB) estimates, there are few data sets available to evaluate the controls over stem rot infection and severity in tropical forests. Using legacy and recent data from 3180 drilled, felled, and cored stems in mixed dipterocarp forests in Sarawak, Malaysian Borneo, we quantified the frequency and severity of stem rot in a total of 339 tree species, and related variation in stem rot with tree size, wood density, taxonomy, and species' soil association, as well as edaphic conditions. Predicted stem rot frequency for a 50 cm tree was 53 % of felled, 39 % of drilled, and 28 % of cored stems, demonstrating differences among methods in rot detection ability. The percent stem volume infected by rot, or stem rot severity, ranged widely among trees with stem rot infection (0.1–82.8 %) and averaged 9 % across all trees felled. Tree taxonomy explained the greatest proportion of variance in both stem rot frequency and severity among the predictors evaluated in our models. Stem rot frequency, but not severity, increased sharply with tree diameter, ranging from 13 % in trees 10–30 cm DBH to 54 % in stems ≥ 50 cm DBH across all data sets. The frequency of stem rot increased significantly in soils with low pH and cation concentrations in topsoil, and stem rot was more common in tree species associated with dystrophic sandy soils than with nutrient-rich clays. When scaled to forest stands, the maximum percent of stem biomass lost to stem rot varied significantly with soil properties, and we estimate that stem rot reduces total forest AGB estimates by up to 7 % relative to what would be predicted assuming all stems are composed strictly of intact wood. This study demonstrates not only that stem rot is likely to be a significant source of error in forest AGB estimation, but also that it strongly covaries with tree size, taxonomy, habitat association, and soil resources, underscoring the need to account for tree community composition and edaphic variation in estimating carbon storage in tropical forests.

Escherichia coli YqjA, a Member of the Conserved DedA/Tvp38 Membrane Protein Family, Is a Putative Osmosensing Transporter Required for Growth at Alkaline pH.

The ability to persist and grow under alkaline conditions is an important characteristic of many bacteria. In order to survive at alkaline pH, Escherichia coli must maintain a stable cytoplasmic pH of about 7.6. Membrane cation/proton antiporters play a major role in alkaline pH homeostasis by catalyzing active inward proton transport. The DedA/Tvp38 family is a highly conserved membrane protein family of unknown function present in most sequenced genomes. YqjA and YghB are members of the E. coli DedA family with 62% amino acid identity and partially redundant functions. We have shown that E. coli with ΔyqjA and ΔyghB mutations cannot properly maintain the proton motive force (PMF) and is compromised in PMF-dependent drug efflux and other PMF-dependent functions. Furthermore, the functions of YqjA and YghB are dependent upon membrane-embedded acidic amino acids, a hallmark of several families of proton-dependent transporters. Here, we show that the ΔyqjA mutant (but not ΔyghB) cannot grow under alkaline conditions (ranging from pH 8.5 to 9.5), unlike the parent E. coli. Overexpression of yqjA restores growth at alkaline pH, but only when more than ∼100 mM sodium or potassium is present in the growth medium. Increasing the osmotic pressure by the addition of sucrose enhances the ability of YqjA to support growth under alkaline conditions in the presence of low salt concentrations, consistent with YqjA functioning as an osmosensor. We suggest that YqjA possesses proton-dependent transport activity that is stimulated by osmolarity and that it plays a significant role in the survival of E. coli at alkaline pH. The ability to survive under alkaline conditions is important for many species of bacteria. Escherichia coli can grow at pH 5.5 to 9.5 while maintaining a constant cytoplasmic pH of about 7.6. Under alkaline conditions, bacteria rely upon proton-dependent transporters to maintain a constant cytoplasmic pH. The DedA/Tvp38 protein family is a highly conserved but poorly characterized family of membrane proteins. Here, we show that the DedA/Tvp38 protein YqjA is critical for E. coli to survive at pH 8.5 to 9.5. YqjA requires sodium and potassium for this function. At low cation concentrations, osmolytes, including sucrose, can facilitate rescue of E. coli growth by YqjA at high pH. These data are consistent with YqjA functioning as an osmosensing cation-dependent proton transporter.

Hydrogeochemical characterization of a shallow groundwater system in the weathered basement aquifer of Ilesha area, southwestern Nigeria

Abstract. Hydrogeochemical characterization of a weathered basement aquifer in Ilesha area, southwest Nigeria, was carried out with respect to geogenic and anthropogenic influences on the shallow groundwater system. Physico-chemical parameters revealed a pH of 6.4–8.4 and EC of 22–825 μs/cm in the urban areas compared to a pH of 7.3–10.5 and relatively higher EC of 126–1027 μs/cm in the peri-urban area. The concentrations of major cations (Ca, Na, K, Mg) in the urban areas revealed relatively lower average concentrations of 28.4, 16.7, 8.4 and 5.0 mg/L, respectively, compared to 82.5, 33.4, 19.3 and 12.4 mg/L, respectively, for the peri-urban areas. The low concentrations of major cations in the urban areas can be attributed to low mineral dissolution of quartzite and muscovite quartz-schist bedrocks compared to the weathered granitic, amphibolite and biotite schist in the peri-urban areas. Hydrochemical characterization revealed two main water types; namely Ca-Mg-(Na)-HCO3 mostly in the urban areas suggesting CO2-charged infiltrating recharge rainwater, and Ca-Na-(K)-SO4-Cl type in the peri-urban areas as products of water–rock interactions.

Reversibly tunable helix inversion in supramolecular gels trigged by Co(2+).

Terpyridine-based ligands form octahedral complexes with Co(2+) at low cation concentrations to form helical assemblies which provide a supramolecular gel framework. Increasing the Co(2+) concentration above 0.6 equiv. reveals a second, co-existing square pyramidal complex derived assembly, having a distinct helicity. While this geometry dominates at 1 equiv. of Co(2+), we find this unique form of helical inversion to be fully reversible and controllable.

Cloning and Characterization of a Wheat Homologue of Apurinic/Apyrimidinic Endonuclease Ape1L

BackgroundApurinic/apyrimidinic (AP) endonucleases are key DNA repair enzymes involved in the base excision repair (BER) pathway. In BER, an AP endonuclease cleaves DNA at AP sites and 3′-blocking moieties generated by DNA glycosylases and/or oxidative damage. A Triticum aestivum cDNA encoding for a putative homologue of ExoIII family AP endonucleases which includes E. coli Xth, human APE1 and Arabidopsis thaliana AtApe1L has been isolated and its protein product purified and characterized.Methodology/Principal FindingsWe report that the putative wheat AP endonuclease, referred here as TaApe1L, contains AP endonuclease, 3′-repair phosphodiesterase, 3′-phosphatase and 3′→5′ exonuclease activities. Surprisingly, in contrast to bacterial and human AP endonucleases, addition of Mg2+ and Ca2+ (5–10 mM) to the reaction mixture inhibited TaApe1L whereas the presence of Mn2+, Co2+ and Fe2+ cations (0.1–1.0 mM) strongly stimulated all its DNA repair activities. Optimization of the reaction conditions revealed that the wheat enzyme requires low divalent cation concentration (0.1 mM), mildly acidic pH (6–7), low ionic strength (20 mM KCl) and has a temperature optimum at around 20°C. The steady-state kinetic parameters of enzymatic reactions indicate that TaApe1L removes 3′-blocking sugar-phosphate and 3′-phosphate groups with good efficiency (k cat/K M = 630 and 485 μM−1·min−1, respectively) but possesses a very weak AP endonuclease activity as compared to the human homologue, APE1.Conclusions/SignificanceTaken together, these data establish the DNA substrate specificity of the wheat AP endonuclease and suggest its possible role in the repair of DNA damage generated by endogenous and environmental factors.

Synthesis, characterization and in vitro toxicity assessment of DMPS-capped CdTe quantum dots

The title water-soluble thiol-capped QDs (quantum dots) were synthesized by reacting CdCl2, DMPS and NaHTe in a water medium [DMPS is sodium 2,3-bis(sulfanyl)propane-1-sulfonate]. The nanoparticles were characterized by UV–Vis, fluorescence and FT-IR spectroscopy, transmission electron microscopy (TEM) and powder XRD measurements. The QDs are spherical, with an average diameter of 3.4±0.7nm and good stability against photooxidation and photobleaching. The influence of a wide number of anions and cations on the fluorescence emission of the nanoparticles has been explored. At a low metal cation concentration (5μM), only Hg(II) produces the total quenching of the QD photoemission. At higher concentrations, Cu(II), Ag(I), Pb(II) and Ni(II) also induce a significant quenching. A preliminary analysis of the QD cytotoxicity on HeLa 229 and LLC-PK1 line cells was performed using the MTT assay. In 2h incubation experiments, high cell-viability was observed, but this parameter decreases significantly after 24h incubation. During this longer incubation period only the LLC-PK1 cells maintained a good metabolic activity when [QDs] is ⩽5μg/mL. Accordingly, fluorescence confocal microscopy indicated that the uptake of the nanoparticles is apparently higher in HeLa cells than in LLC-PK1 cells.

Formation and crystallization of Mg2 +–Fe3 +–SO42 −–CO32 −-type anionic clays

Hydrotalcite-like layered double hydroxides (LDHs) is usually produced in the laboratory via co-precipitation. However, the effect of synthesis parameters in contact with the atmosphere on LDH formation and crystallinity has not been studied in detail. The present study evaluated the role of aqueous pH, temperature, and divalent (M2+) to trivalent (M3+) cation ratio on Mg2+Fe3+SO42−CO32−-type LDH formation as well as the role of dissolved M2++M3+ concentrations, drying temperature, rate of cation supply, and aging temperature and time on the crystallinity of the LDH. Formation of hydrotalcite-like anionic clays was facilitated at pH ≥9, M2+/M3+ ≥0.75, and 0–75°C, with high pH and M2+/M3+ ratio enhancing the degree of crystallinity. Low cation concentrations and high cation availability (high cation supply rate) resulted in better developed crystals. High M3+ concentration (M2+/M3+=0.5) and pH <9 favored formation of ferric hydroxide precipitates, which subsequently led to formation of Mg2+Fe3+-rich LDHs via continuous Mg2+ substitution where CO32− and SO42− acted as charge balancing anions. Aging for <24h enhanced crystallinity. For times >24h lower degrees of crystallinity were observed as was enhanced cation ordering and increased crystal size. Drying immediately after precipitation resulted in crystal structural disorder.

Effects of Acidic Deposition and Soil Acidification on Sugar Maple Trees in the Adirondack Mountains, New York

We documented the effects of acidic atmospheric deposition and soil acidification on the canopy health, basal area increment, and regeneration of sugar maple (SM) trees across the Adirondack region of New York State, in the northeastern United States, where SM are plentiful but not well studied and where widespread depletion of soil calcium (Ca) has been documented. Sugar maple is a dominant canopy species in the Adirondack Mountain ecoregion, and it has a high demand for Ca. Trees in this region growing on soils with poor acid-base chemistry (low exchangeable Ca and % base saturation [BS]) that receive relatively high levels of atmospheric sulfur and nitrogen deposition exhibited a near absence of SM seedling regeneration and lower crown vigor compared with study plots with relatively high exchangeable Ca and BS and lower levels of acidic deposition. Basal area increment averaged over the 20th century was correlated (p < 0.1) with acid-base chemistry of the Oa, A, and upper B soil horizons. A lack of Adirondack SM regeneration, reduced canopy condition, and possibly decreased basal area growth over recent decades are associated with low concentrations of nutrient base cations in this region that has undergone soil Ca depletion from acidic deposition.

204Tl tracer diffusion and conductivity in thallium thiogermanate glasses

Abstract Conductivity and 204Tl tracer diffusion measurements have been carried out in the (Tl2S)x(GeS)60(GeS2)40 − x glassy system, where the Tl2S concentration changes between 0 ≤ x ≤ 25. The room temperature dc conductivity increases by 7 orders of magnitude with increasing thallium concentration, ranging between 10− 18 S cm− 1 for the 60GeS-40GeS2 matrix and 10− 11 S cm− 1 for Tl2S-rich glasses. The activation energy decreases from 1.22 to 0.79 eV, respectively. The conductivity and thallium diffusion results reveal that the ionic transport becomes to be predominant at high thallium concentrations (≈ 15 at.% Tl). The thallium ion transport number t Tl + increases from 10− 3 for low cation concentrations to t Tl + ≅ 1 for the x = 20 sample. The Haven ratio, HR ≈ 1, indicates uncorrelated ion motion even at rather high thallium concentrations. The obtained results are discussed in comparison with similar (Ag2S)x(GeS)60(GeS2)40 − x glassy system.

The phenothiazine-class antipsychotic drugs prochlorperazine and trifluoperazine are potent allosteric modulators of the human P2X7 receptor

P2X7, an ATP-gated cation channel, is involved in immune cell activation, hyperalgesia and neuropathic pain. By regulating cytokine release in the brain, P2X7 has been linked to the pathophysiology of mood disorders and schizophrenia. We here assess the impact of 123 drugs that act in the central nervous system on human P2X7. Most prominently, the tricyclic antipsychotics prochlorperazine (PCP) and trifluoperazine (TFP) potently inhibited P2X7-mediated Ca2+ entry, dye permeation and ionic currents. In divalent cation-containing bath solutions or after prolonged incubation, ATP-evoked P2X7 currents were inhibited by 10 μM PCP. This effect was not related to dopamine receptor antagonism. Surprisingly, PCP co-applied with ATP enhanced inward currents in bath solutions with low divalent cation concentrations. Intracellular perfusion with PCP did not substitute for the extracellularly applied drug, indicating that its binding sites are accessible from the extracellular space. Since P2X7 current potentiation by PCP was voltage-dependent, at least one site may be located within the electrical field of the membrane. While the channel opening and closure kinetic was altered by PCP, the apparent affinity of ATP remained unchanged (potentiation) or changed slightly (inhibition). Measurements in human monocyte-derived macrophages confirmed the PCP-induced inhibition of ATP-evoked Ca2+ influx, Yo-Pro-1 permeability, and whole cell currents. Interestingly, neither heterologously expressed rat or mouse P2X7 nor native P2X7 in rat astrocyte cultures or in mouse bone marrow-derived macrophages were inhibited by perazines with a similar potency. We conclude that perazine-type neuroleptics are potent, but species-selective allosteric modulators of human but not murine P2X7 receptors.

Groundwater acidification near the water table of the Superficial aquifer, Gnangara Mound, Swan Coastal Plain, Western Australia

This study improves the spatial understanding of the magnitude of the groundwater acidification issue in a poorly buffered sandy aquifer in Western Australia. The study provides more information to assess the risk the acidification poses to groundwater dependent ecosystems of the Gnangara Mound. Groundwater acidification (pH<5) was identified on a regional scale, mainly due to pyrite oxidation, with the lowest pH of 3.13. Groundwater was fresh (TDS<500mg/L) with low concentrations of base cations, negligible alkalinity (<10mg/L as CaCO3), high SO42-/Cl- ratios (>0.5mg/L units), low Ca to Al molar ratios and elevated concentrations of Al and Fe.Acidic groundwater in the capture zones of wetlands may pose a long term risk to ecological values. Acidic groundwater in poorly buffered systems also poses a risk for users of untreated groundwater. Land and water use management should consider poorly buffered aquifers to be highly sensitive, particularly where rainfall and recharge trends have declined over a period of time. A comprehensive and consistent groundwater sampling program should be developed to fully delineate the groundwater acidification issue near the water table of the Gnangara Mound to assist the formulation of groundwater allocation plans.

DNA A-tracts are not curved in solutions containing high concentrations of monovalent cations.

The intrinsic curvature of seven 98 bp DNA molecules containing up to four centrally located A6-tracts has been measured by gel and capillary electrophoresis as a function of the number and arrangement of the A-tracts. At low cation concentrations, the electrophoretic mobility observed in polyacrylamide gels and in free solution decreases progressively with the increasing number of phased A-tracts, as expected for DNA molecules with increasingly curved backbone structures. Anomalously slow electrophoretic mobilities are also observed for DNA molecules containing two pairs of phased A-tracts that are out of phase with each other, suggesting that out-of-phase distortions of the helix backbone do not cancel each other out. The mobility decreases observed for the A-tract samples are due to curvature, not cation binding in the A-tract minor groove, because identical free solution mobilities are observed for a molecule with four out-of-phase A-tracts and one with no A-tracts. Surprisingly, the curvature of DNA A-tracts is gradually lost when the monovalent cation concentration is increased to ∼200 mM, regardless of whether the cation is a hydrophilic ion like Na+, NH4+, or Tris+ or a hydrophobic ion like tetrabutylammonium. The decrease in A-tract curvature with increasing ionic strength, along with the known decrease in A-tract curvature with increasing temperature, suggests that DNA A-tracts are not significantly curved under physiological conditions.

Gradual and anthropogenic soil change for fertility and carbon on marginal sandy soils

As soils come under increasing pressure to maintain a range of ecosystem services, there is interest in how soils change over time in response to factors such as change in land-use. Many studies examining long- and short-term soil change have focused on soils with relatively high mineral and fertility status. Therefore, the aims of this study are to explore regional change on a marginal sandy soil formed over the Sherwood Sandstone outcrop in Nottinghamshire, U.K. (750km2) and to assess changes in soil fertility as a function of the natural weathering process and land use change. The study uses data from three sources to examine differences between soil fertility properties under two major land-uses through the depth of the soil/mobile regolith (~1.6m) and into the saprolite. It is proposed that the differences reflect in part the result of historical change in land-use. From old maps we identify the land-use changes back to 1781. This allowed us to compare soils that have been under woodland cover at least since 1781 with those that were converted to arable use in major deforestation between 1781 and 1881. Soils now under woodland have low concentrations of base cations, an acid pH and a mean organic carbon concentration (0–15cm) of 2.7%. In contrast soils now under arable use have large concentrations of base cations, pH close to neutral and mean organic carbon concentration (0–15cm) of 1.7%. There is evidence in the arable soils of leaching to depth of materials from applied fertilisers and lime. These results show the rapid change in properties of soil formed in bedrock, with small concentrations of nutrients and weatherable minerals, which can result from land-use change.

Temperature dependence of the structural, magnetic, and magnetostrictive properties of zinc-substituted cobalt ferrite

This study presents the effects of substitution of Zn2+ for Co2+ at low concentrations and the effects of temperature variations on the structural, magnetic, and magnetostrictive properties of cobalt ferrite. Although the Zn-substituted cobalt ferrite samples, Co1−xZnxFe2O4 (x = 0.02, 0.04, 0.06, 0.09, and 0.17) did not show observable changes in crystal structure, the magnetic and magnetostrictive properties were strongly affected. The variation in magnetic susceptibility with composition can be related to the variations in magnetization, coercive field and magnetocrystalline anisotropy. The changes in coercive field were found to be primarily due to the variations in the magnetocrystalline anisotropy. The effect of magnetocrystalline anisotropy on magnetization was stronger at lower cation concentration than at higher concentrations. The decrease in magnetization around 150 K is attributed to the high magnetocrystalline anisotropy at low temperatures which prevented the maximum applied field of 4 MA/m from causing the saturation of magnetization in the samples. Because the magnetocrystalline anisotropy was determined with the magnetization data using the Law of Approach to saturation magnetization, the reliability of the result was found to decrease with decrease in temperature. Peak-to-peak magnetostriction amplitude and the strain sensitivity decreased with increase in Zn substitution.

Enzyme characterisation and gene expression profiling of Atlantic salmon chicken- and goose-type lysozymes

Lysozymes represent important innate immune components against bacteria. In this study, Atlantic salmon (Salmo salar) goose (g-) and chicken (c-) types of lysozyme were subjected to protein characterisations and tissue expression analyses. Specific bacterial protein inhibitors of g- and c-type lysozymes were employed to discriminate between respective enzyme activities. Blood, gills and liver contained activities exclusive for the g-type lysozyme. Only haematopoietic organs (head kidney and spleen) contained enzyme activities of both g- and c-lysozyme enzymes and c-type activity was not found outside these organs. Gene transcript levels proportional to enzyme activity levels were detected for the g-type lysozyme but not for the c-type. In vitro studies revealed significant induction of c-type gene expression and enzyme activity in macrophages after incubation with lipopolysaccharide (LPS) while expression of the g-type lysozyme gene was unaffected. The activity of purified native c-type enzyme was profoundly reduced by divalent cations and displayed low tolerance to monovalent cations, while the native g-type lysozyme was stimulated by monovalent cations and tolerated low concentrations of divalent cations. Activities of both enzymes increased with temperature elevations up to 60°C. The native g-type lysozyme responses to temperature in particular are in apparent conflict to the ones for the recombinant salmon g-lysozyme.Our results imply separate expression regulations and different functions of c- and g-type lysozymes in salmon. LPS-induced expression of c-type lysozyme and broad constitutive tissue distribution of g-type lysozyme in salmon is different from findings in other studied fish species.

Interacting effects of wildfire severity and liming on nutrient cycling in a southern Appalachian wilderness area

Aims Wilderness and other natural areas are threatened by large-scale disturbances (e.g., wildfire), air pollution, climate change, exotic diseases or pests, and a combination of these stress factors (i.e., stress complexes). Linville Gorge Wilderness (LGW) is one example of a high elevation wilderness in the southern Appalachian region that has been subject to stress complexes including chronic acidic deposition and several wildfires, varying in intensity and extent. Soils in LGW are inherently acidic with low base cation concentrations and decades of acidic deposition have contributed to low pH, based saturation, and Ca:Al ratio. We hypothesized that wildfires that occurred in LGW followed by liming burned areas would accelerate the restoration of acidic, nutrient depleted soils. Because soils at LGW had extremely low concentrations of exchangeable Ca 2+ and Mg 2+ dolomitic lime was applied to further boost these cations. We evaluated the effectiveness of dolomitic lime application in restoring exchangeable Ca 2+ and Mg 2+ and subsequently increasing pH and Ca:Al ratio of soils and making Ca and Mg available to recovering vegetation. Methods Five treatment areas were established: severely burned twice (2000 & 2007) with dolomitic lime application (2xSBL); moderately burned twice with lime application (2xMBL); severely burned twice, unlimed (2xSB); moderately burned once (2000), unlimed (1xMB); and a reference area (REF; unburned, unlimed). In 2008 and 2009, we measured overstory, understory, and ground-layer vegetation; forest floor mass and nutrients; and soil and soil solution chemistry within each treatment area. Results All wildfire burned sites experienced substantial overstory mortality. However, understory biomass doubled between sample years on the most recently burned sites due to the rapid regrowth of ericaceous shrubs and prolific sprouting of deciduous trees. Burning followed by lime application (2xSBL and 2xMBL) significantly increased shallow soil solution NO3-N, but we found no soil solution NO3-N response to burning alone (2xSB and 1xMB). Surface soil base saturation and exchangeable Ca 2+ were significantly affected by liming; Ca 2+ concentrations were greater on 2xMBL and 2xSBL than 2xSB, 1xMB and REF.

Lipid bilayer – DNA interaction mediated by divalent metal cations: SANS and SAXD study

The structure of aggregates formed due to DNA interaction with dipalmitoylphosphatidylcholine (DPPC) in presence of Ca2+ and Zn2+ is examined using small-angle synchrotron X-ray diffraction (SAXD) and small-angle neutron scattering (SANS). SAXD detected two structures: LC - condensed lamellar phase and LX - lamellar phase with DNA strands intercalated between the adjacent lipid bilayers, without regular packing at low cation concentration (∼1 mM). The high concentration of Zn2+ induces a macroscopic phase separation in mixtures. The SANS curves of DPPC+ions2+ vesicles evaluated using the strip function model have shown different modes of cations binding to the DPPC bilayers.

Na+,K+-ATPase Activity in the Posterior Gills of the Blue Crab, Callinectes ornatus (Decapoda, Brachyura): Modulation of ATP Hydrolysis by the Biogenic Amines Spermidine and Spermine

We investigated the effect of the exogenous polyamines spermine, spermidine and putrescine on modulation by ATP, K⁺, Na⁺, NH₄⁺ and Mg²⁺ and on inhibition by ouabain of posterior gill microsomal Na⁺,K⁺-ATPase activity in the blue crab, Callinectes ornatus, acclimated to a dilute medium (21‰ salinity). This is the first kinetic demonstration of competition between spermine and spermidine for the cation sites of a crustacean Na⁺,K⁺-ATPase. Polyamine inhibition is enhanced at low cation concentrations: spermidine almost completely inhibited total ATPase activity, while spermine inhibition attained 58%; putrescine had a negligible effect on Na⁺,K⁺-ATPase activity. Spermine and spermidine affected both V and K for ATP hydrolysis but did not affect ouabain-insensitive ATPase activity. ATP hydrolysis in the absence of spermine and spermidine obeyed Michaelis-Menten behavior, in contrast to the cooperative kinetics seen for both polyamines. Modulation of V and K by K⁺, Na⁺, NH₄⁺ and Mg²⁺ varied considerably in the presence of spermine and spermidine. These findings suggest that polyamine inhibition of Na⁺,K⁺-ATPase activity may be of physiological relevance to crustaceans that occupy habitats of variable salinity.