Effects of the dipolar form of phloretin on potassium conductance in squid giant axons.

The effects of phloretin on membrane ionic conductances have been studied in the giant axon of the squid, Loligo pealei. Phloretin reversibly suppresses the potassium and sodium conductances and modifies their dependence on membrane potential (Em). Its effects on the potassium conductance (GK) are much greater than on the sodium conductance; no effects on sodium inactivation are observed. Internal perfusion of phloretin produces both greater shifts in GK(Em) and greater reductions maximum GK than does external perfusion; the effect of simultaneous internal and external perfusion is little greater than that of internal perfusion alone. Lowering the internal pH, which favors the presence of the neutral species of weakly acidic phloretin (pKa 7.4), potentiates the actions of internally perfused phloretin. Other organic cations with dipole moments similar to phloretin's have little effect on either potassium or sodium conductances in squid axons. These results can be explained by either of two mechanisms; on postulates a phloretin "receptor" near the voltage sensor component of the potassium channel which is accessible to drug molecules applied at either the outer or inner membrane surface and is much more sensitive to the neutral than the negatively charged form of the drug. The other mechanism proposes that neutral phloretin molecules are dispersed in an ordered array in the membrane interior, producing a diffuse dipole field which modifies potassium channel gating. Different experimental results support these two mechanisms, and neither hypothesis can be disproven.     

Mineral uptake and transport in xylem and phloem of the proteaceous tree,Banksia prionotes

Xylem sap of sinker (tap) root, cluster feeding roots, lateral roots and from an age series of main stem extensions of 6-year trees of Banksia prionotes was collected and analyzed for principal organic and inorganic solutes. During the phase of root uptake activity in winter and spring, cluster roots were principal xylem donors of malate, phosphate, chloride, sodium, potassium and amino acid N whereas other parts of the root served as major sources to the shoot of other cations, nitrate and sulphate. Sinker root xylem sap was at all times less concentrated in solutes than that of lateral roots into which cluster roots were voiding exported solutes. Phosphate was abstracted from xylem by stem tissue during winter and it and a range of other solutes released back to xylem immediately prior to extension growth of the shoot in summer. Phloem sap collected from mid regions of stems was unusually low in potassium and phosphate relative to chloride and sulphate in comparison with phloem sap of other species, and its low potassium: sodium ratio relative to xylem indicated poor discrimination against sodium during phloem loading. Data are discussed in relation to the asynchronous seasonal cycles of nutrient uptake and shoot growth.     

Structure, dynamics, and hydration of POPC/POPS bilayers suspended in NaCl, KCl, and CsCl solutions

Effects of alkali metal chlorides on the properties of mixed negatively charged lipid bilayers are experimentally measured and numerically simulated. Addition of 20mol% of negatively charged phosphatidylserine to zwitterionic phosphatidylcholine strengthens adsorption of monovalent cations revealing their specificity, in the following order: Cs(+)相似文献   

Diffusion, Exclusion, and Specific Binding in a Large Channel: A Study of OmpF Selectivity Inversion

We find that moderate cationic selectivity of the general bacterial porin OmpF in sodium and potassium chloride solutions is inversed to anionic selectivity in concentrated solutions of barium, calcium, nickel, and magnesium chlorides. To understand the origin of this phenomenon, we consider several factors, which include the binding of divalent cations, electrostatic and steric exclusion of differently charged and differently sized ions, size-dependent hydrodynamic hindrance, electrokinetic effects, and significant “anionic” diffusion potential for bulk solutions of chlorides of divalent cations. Though all these factors contribute to the measured selectivity of this large channel, the observed selectivity inversion is mostly due to the following two. First, binding divalent cations compensates, or even slightly overcompensates, for the negative charge of the OmpF protein, which is known to be the main cause of cationic selectivity in sodium and potassium chloride solutions. Second, the higher anionic (versus cationic) transport rate expected for bulk solutions of chloride salts of divalent cations is the leading cause of the measured anionic selectivity of the channel. Interestingly, at high concentrations the binding of cations does not show any pronounced specificity within the divalent series because the reversal potentials measured in the series correlate well with the corresponding bulk diffusion potentials. Thus our study shows that, in contrast to the highly selective channels of neurophysiology that employ mostly the exclusion mechanism, quite different factors account for the selectivity of large channels. The elucidation of these factors is essential for understanding large channel selectivity and its regulation in vivo.     

CATION UPTAKE BY INTACT NUCLEI FROM RAT CEREBRAL CORTEX

A method is described for determining the uptake of cations by intact nuclei from rat cerebral cortex. The divalent cations of magnesium, manganese and calcium were found to be concentrated in the nuclear pellet to levels well above the initial concentration of the medium, whereas little uptake of either potassium or sodium was observed. The binding of divalent cations to the nuclei will produce a cationic environment quite different from that of the external medium. Such localized differences may play a role in the control of nuclear activities.     

Monovalent cations and their influence on activated sludge floc chemistry, structure, and physical characteristics

Multivalent cations have been known to be important components of activated sludge floc structure due to their bridging ability of the negatively charged sites on the biopolymer network. Recently in batch systems it was found that excess concentration of monovalent cations led to the deterioration in settleability, dewaterability of sludges and effluent quality of the system. In this study, effect of influent monovalent cations (potassium and sodium) on activated sludge floc structure was investigated in semi-continuous reactors. Results revealed that the increase in concentration of both ions correlated to the general increase in total EPS concentration. The zeta potential values were affected by the cation type and dose in such a way that sludge from sodium reactors had always higher zeta potential values (higher negative charge) than the sludges from potassium reactors. Flocs from sodium reactors were more fragile and weak and the capillary suction time values of these sludges were higher compared to those from potassium reactors. The findings of this research conclude that the floc structure is significantly weakened with the increase of monovalent cations. Even though EPS is produced, it is unable to bind the floc components together. With this, the physical properties of sludge deteriorate for both cations.     

Electrostatic basis of valence selectivity in cationic channels

We examine how a variety of cationic channels discriminate between ions of differing charge. We construct models of the KcsA potassium channel, voltage gated sodium channel and L-type calcium channel, and show that they all conduct monovalent cations, but that only the calcium channel conducts divalent cations. In the KcsA and sodium channels divalent ions block the channel and prevent any further conduction. We demonstrate that in each case, this discrimination and some of the more complex conductance properties of the channels is a consequence of the electrostatic interaction of the ions with the charges in the channel protein. The KcsA and sodium channels bind divalent ions strongly enough that they cannot be displaced by other ions and thereby block the channel. On the other hand, the calcium channel binds them less strongly such that they can be destabilized by the repulsion of another incoming divalent ion, but not by the lesser repulsion from monovalent ions.     

Electrostatic basis of valence selectivity in cationic channels

We examine how a variety of cationic channels discriminate between ions of differing charge. We construct models of the KcsA potassium channel, voltage gated sodium channel and L-type calcium channel, and show that they all conduct monovalent cations, but that only the calcium channel conducts divalent cations. In the KcsA and sodium channels divalent ions block the channel and prevent any further conduction. We demonstrate that in each case, this discrimination and some of the more complex conductance properties of the channels is a consequence of the electrostatic interaction of the ions with the charges in the channel protein. The KcsA and sodium channels bind divalent ions strongly enough that they cannot be displaced by other ions and thereby block the channel. On the other hand, the calcium channel binds them less strongly such that they can be destabilized by the repulsion of another incoming divalent ion, but not by the lesser repulsion from monovalent ions.     

Ca2+, Mg2+, Li+, Na+, and K+ distributions in the headgroup region of binary membranes of phosphatidylcholine and phosphatidylserine as seen by deuterium NMR

The binding of calcium, magnesium, lithium, potassium, and sodium to membrane bilayers of 5 to 1 (M/M) 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and 1-palmitoyl- 2-oleoylphosphatidylserine (POPS) was investigated by using deuterium nuclear magnetic resonance (2H NMR). Both lipids were deuteriated on their polar headgroups, and spectra were obtained at 25 degrees C in the liquid-crystalline phase as a function of salt concentration. The spectra obtained with calcium were correlated with 45CaCl2 binding studies to determine the effective membrane-bound calcium at low calcium binding, up to 0.78 calcium per POPS. Deuterium quadrupolar splittings of both POPC and POPS headgroups were shown to be very sensitive to calcium binding. The behavior of these two headgroups over a wide range of CaCl2 concentrations suggests that Ca2+ binding occurs in at least two steps, the first step being achieved with 0.5 M CaCl2, with a stoichiometry of 0.5 Ca2+ per POPS. Correlations of the deuterium Ca2+ binding data with related data obtained after incorporation of a cationic integral peptide showed that the effects of these two cationic molecules of the POPS headgroup are qualitatively similar, and provided further support for two-step Ca2+ binding to the POPC/POPS 5:1 membranes. The corresponding data obtained with magnesium, lithium, and potassium indicate that these cations interact with both the choline and serine headgroups. The amplitudes of headgroup perturbations could be partly correlated to the relative affinities of the metallic cations for the lipid membrane. The two-step binding described with Ca2+ appears to be relevant to the Mg2+ data, and in certain limits to the Li+ data. The data were interpreted in terms of conformational changes of the lipid headgroups induced by an electric field due to the charges of the membrane-bound metallic cations. A conformational change of the serine headgroup induced by the membrane-bound charges is proposed. We propose that the metallic cations can be differentiated on the basis of their respective spatial distribution functions relative to the choline and serine headgroups. According to this interpretation, the divalent cations Ca2+ and Mg2+ are more deeply buried in the membrane than monovalent Na+ and K+, the case of Li+ being intermediate of the latter two. This conclusion is discussed in relation to fundamental theories of the spatial distribution of ions near the interface between water and smooth charged solid surfaces.     

响应面法优化火麻仁油微胶囊喷雾干燥工艺的研究

为了制备包埋率高、稳定性好的火麻仁油微胶囊,拓展其在食品领域的应用范围,以火麻仁油为芯材、单双脂肪酸甘油酯为乳化剂、酪蛋白酸钠为壁材、固体玉米糖浆为填充剂、柠檬酸钠为缓冲盐、抗坏血酸棕榈酸钠为抗氧化剂,通过喷雾干燥法制备60%载油率的火麻仁油微胶囊,以微胶囊包埋率为响应值,在单因素实验的基础上,以干物浓度、进风温度、出风温度为实验因素,采用Box-Behnken响应面分析法进行优化。随后通过扫描电镜观察火麻仁油微胶囊表面形态结构,以确定包埋效果。并利用油脂氧化分析仪检测火麻仁油微胶囊的氧化稳定性。研究确定微胶囊的最佳工艺条件为：干物浓度42%、进风温度168 ℃、出风温度74 ℃,在此条件下制备得到的火麻仁油微胶囊包埋率可达92.15%。通过扫描电镜观察到火麻仁油微胶囊表面圆滑无裂痕,表明火麻仁油微胶囊包埋效果比较理想。经油脂氧化分析仪测定,与对照组（火麻仁油）相比,试验组（火麻仁油微胶囊）的氧化诱导期时间较长,能够达到30 h以上,说明通过对火麻仁油进行微胶囊包埋可以较大程度地提高油脂的稳定性。研究结果为火麻仁油在食品工业领域的开发和应用提供了理论支持。     

Preferential recombination between GC clusters in yeast mitochondrial DNA.

Yeast mitochondrial DNA molecules have long, AT-rich intergenic spacers punctuated by short GC clusters. GC-rich elements have previously been characterized by others as preferred sites for intramolecular recombination leading to the formation of subgenomic petite molecules. In the present study we show that GC clusters are favored sites for intermolecular recombination between a petite and the wild-type grande genome. The petite studied retains 6.5 kb of mitochondrial DNA reiterated tandemly to form molecules consisting of repeated units. Genetic selection for integration of tandem 6.5 kb repeats of the petite into the grande genome yielded a novel recombination event. One of two crossovers in a double exchange event occurred as expected in the 6.5 kb of matching sequence between the genomes, whereas the second exchange involved a 44 bp GC cluster in the petite and another 44 bp GC cluster in the grande genome 700 bp proximal to the region of homology. Creation of a mitochondrial DNA molecule with a repetitive region led to secondary recombination events that generated a family of molecules with zero to several petite units. The finding that 44 bp GC clusters are preferred as sites for intermolecular exchange adds to the data on petite excision implicating these elements as recombinational hotspots in the yeast mitochondrial genome.     

Study on the diuretic activity of Strychnos potatorum Linn. seed extract in albino rats

Methanol extract of Strychnos potatorum Linn. seeds (SPSE) was evaluated for its diuretic activity in Wistar albino rats. The SPSE was administered at the graded doses of 200, 400, and 600 mg/kg body weight. The parameters which were taken into account during the experimental on each rat were: total urine volume (corrected for water intake during the test period), body weight before and after the experiment, and the concentration of sodium, potassium, and chloride ions in urine. The total urine volumes of the SPSE (600 mg/kg)-treated rats were evaluated nearly two and half fold then compared with the control (saline treated) group. Excretion of cations (sodium and potassium ions) and anions (chloride ions) also increased significantly with respect to the control group. The diuretic effect was comparable with that of the standard drug Furosemide. The increase of cations in the urine on treatment with Strychnos potatorum seed extract (SPSE) was dose-dependent. This effect supports the use of the Strychnos potatorum seeds as a diuretic in folk remedies.     

Proportional equilibration of K, Na ions, and sucrose molecules in pig lenses incubated in the presence of the non-ionic detergent Triton X-100

The release of sodium and potassium and the uptake of sucrose molecules was studied in pig lenses incubated in isosmotic sucrose solution in either the presence or absence of 1% Triton X-100 (a non-ionic detergent). This Triton X-100 treatment has been shown to cause severe disruptions of cell membrane integrity. If sodium and potassium were free in the lens fibers as in a dilute aqueous solution, they would be expected to diffuse three to four times faster than sucrose. However, measurements of sodium and potassium release and sucrose uptake in the Triton X-100 treated lenses show a 1:1 equilibration. When pig lenses were incubated in the same solution without detergent, the sucrose uptake was significantly less than the potassium and sodium release. It is postulated that a slow, detergent mediated collapse of protein-water-ion interactions within the lens is the rate-limiting step of the observed equilibration of monovalent cations and sucrose molecules.     

The mechanism of energy-dependent ion transport in mitochondria

Summary The transport of potassium, sodium and various anions in rat-liver mitochondria was studied mainly by analysis of ion content and water compartmentation of the mitochondrial pellet. A comparison of spontaneous transport with valinomycin- or gramicidin-stimulated transport is made. The rate or extent of uptake, the internal concentrations and the concentration ratio (C_in/C_out) are calculated and compared to test existing models for ion transport in mitochondria.Several models of ion transport in mitochondria are based on a cation-pump which is directed inward. This hypothesis is rejected because of the following findings: (1) Valinomycin stimulates the rate of potassium uptake but does not increase the potassium concentration ratio that can be actively maintained in a steady state (in which there is no potassium flow). (2) Valinomycin greatly stimulates the efflux of⁴²K from mitochondria during the process of potassium accumulation. When potassium accumulation is stimulated the flux ratio, i.e. influx/efflux, decreases; in the presence of valinomycin this ratio approaches 1. (3) In the presence of gramicidin, the concentration ratios of potassium and sodium are about the same under a variety of conditions. These findings indicate that potassium and sodium transport are passive processes of relaxation towards electro-chemical equilibrium (of the potassium and sodium). In high external potassium concentrations the extent of potassium uptake is limited by the permeation of anions; of the permeating anions multivalent acids support a higher extent than monovalent acids. It was found that succinate, acetate and oxalate which are transported together with potassium are distributed in accordance with the pH and without any relation to the potassium concentration ratio. These findings are compatible with the hypothesis that an outward-directed proton pump creates an electrical potential gradient, which shifts the equilibrium state for the cations and drives sodium and potassium inward, and also creates proton gradient that is the driving force for anion transport.     

Spearman Correlation Identifies Statistically Significant Gene Expression Clusters in Spinal Cord Development and Injury

An important problem in the analysis of large-scale gene expression data is the validation of gene expression clusters. By examining the temporal expression patterns of 74 genes expressed in rat spinal cord under three different experimental conditions, we have found evidence that some genes cluster together under multiple conditions. Using RT-PCR data from spinal cord development and two sets of microarray data from spinal injury, we applied Spearman correlation to identify clusters and to assign P values to pairs of genes with highly similar temporal expression patterns. We found that 15% of genes occurred in statistically significant pairs in all three experimental conditions, providing both statistical and experimental support for the idea that genes that cluster together are co-regulated. In addition, we demonstrated that DNA microarray and RT-PCR data are comparable, and can be combined to confirm gene expression relationships.     

Cellular ions in intact and denervated muscles of the rat

Summary Tissue composition, membrane potentials and cellular activity of potassium, sodium and chloride have been measured in innervated and denervated rat skeletal muscles incubatedin vitro. After denervation for 3 days, tissue water, sodium and chloride were increased but cellular potassium content and measured activity were little affected, despite a decrease of 16 mV in resting membrane potential which would have necessitated a decrease in cellular potassium activity of almost 50% were potassium distributed at electrochemical equilibrium. These findings, therefore, preclude a decreased electrochemical potential gradient for potassium as the cause of the membrane depolarization characteristic of denervated muscle fibers. Analysis of the data excludes an important contribution of rheogenic sodium transport to the resting potential of innervated muscles. These results strongly support the hypothesis that the decreased membrane potential in denervated fibers reflects a relative increase in the membrane permeability to sodium.     

Surprising roles of electrostatic interactions in DNA-ligand complexes

The positions of cations in x-ray structures are modulated by sequence, conformation, and ligand interactions. The goal here is to use x-ray diffraction to help resolve structural and thermodynamic roles of specifically localized cations in DNA-anthracycline complexes. We describe a 1.34 A resolution structure of a CGATCG(2)-adriamycin(2) complex obtained from crystals grown in the presence of thallium (I) ions. Tl(+) can substitute for biological monovalent cations, but is readily detected by distinctive x-ray scattering, obviating analysis of subtle differences in coordination geometry and x-ray scattering of water, sodium, potassium, and ammonium. Six localized Tl(+) sites are observable adjacent to each CGATCG(2)-adriamycin(2) complex. Each of these localized monovalent cations are found within the G-tract major groove of the intercalated DNA-drug complex. Adriamycin appears to be designed by nature to interact favorably with the electrostatic landscape of DNA, and to conserve the distribution of localized cationic charge. Localized inorganic cations in the major groove are conserved upon binding of adriamycin. In the minor groove, inorganic cations are substituted by a cationic functional group of adriamycin. This partitioning of cationic charge by adriamycin into the major groove of CG base pairs and the minor groove of AT base pairs may be a general feature of sequence-specific DNA-small molecule interactions and a potentially useful important factor in ligand design.     

The effect of monovalent cations on calcium efflux in yeasts

The properties of the calcium efflux system in the yeast Saccharomyces cerevisiae were investigated. After growing the cells overnight in medium containing ⁴⁵Ca, the cells were transferred to medium containing glucose, Hepes buffer (pH 5.2) and monovalent cations. The presence of potassium or sodium in the medium induced efflux of calcium from the cells. The magnitude of the efflux was dependent on the concentration of these cations in the medium. The time course of calcium efflux was analyzed, and two types of exchangeable calcium pools, which turned over at different rates, were detected: ‘Fast turnover’ and ‘slow turnover’. Increase in the concentration of monovalent cations in the medium caused an increase in the fraction of cellular calcium which turned over at a fast rate, and activation of calcium efflux from the ‘slow turnover’ calcium pool. The specific changes in the parameters of calcium efflux induced by monovalent cations were different from those reported previously to be induced by divalent cations. Both processes, i.e. activation of calcium efflux by monovalent and by divalent cations, were found to be additive, indicating that they operate via different mechanisms. Experiments using the respiratory inhibitor Antimycin A, showed that stimulation of calcium efflux by monovalent cations is energy dependent. Lanthanum ions which are known to inhibit calcium influx into yeast cells, inhibitted the activation of calcium efflux by both divalent and monovalent cations. Determination of the cationic composition of the cells indicated that the stimulation of calcium efflux was accompanied by influx of potassium or sodium into the cells.     

Experimental Articles

Volcanic ash (Karymskii Volcano, Kamchatka) stimulated growth of the bacterium Rhodovulum sp. A-20s. The interaction between ash, water, media, and bacteria resulted in changes in the chemical composition of the solutions and ash. The ash-water interaction resulted in release of calcium to the solution, as well as in an increase in the proportions of sodium and calcium among the exchange cations of ash. As a result of the ash-medium interaction, calcium and copper were released to the solution; the exchange sodium cations were substituted by calcium and potassium. As a result of the ash-bacteria interaction, the content of copper in the solution decreased, and the exchange cations of calcium and sodium were actively substituted by potassium and magnesium. An increase in the magnesium content among the exchange cations of ash was especially apparent. The products of bacterial metabolism formed mineral-organic complexes with the ash substrate. The data obtained indicate the biogenic transformation of ash, which may lead to the initial phase of formation of clay minerals from volcanic ashes.     

A Monte Carlo simulation of hydration of xanthine-derivatives and their stacked forms.

Results on a Monte Carlo simulation of the hydration of monomer and possible stacked dimer forms of a purine alkaloid series in 200- and 400-water molecule clusters are presented. Investigation of different purine stacked dimers in a 200-water molecule cluster reveals that for caffeine there exists one, for theophylline two and for theobromine four dimers are energetically favorable. For caffeine, the same energetically favored stacked dimer form is observed in both the 200- and 400-water molecule cluster. The main factor stabilizing the preferred dimer stacks is the change in the interaction between water molecules of the monomer cluster and those water molecules in the dimer cluster.