<Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K, <Superscript>238</Superscript>Pu, <Superscript>239+240</Superscript>Pu and <Superscript>90</Superscript>Sr in biological samples from King George Island (Southern Shetlands) in Antarctica

There are few data reported on radionuclide contamination in Antarctica. The aim of this paper is to report ¹³⁷Cs, ⁹⁰Sr and ^238,239+240Pu and ⁴⁰K activity concentrations measured in biological samples collected from King George Island (Southern Shetlands, Antarctica), mostly during 2001–2002. The samples included: bones, eggshells and feathers of penguin Pygoscelis papua, bones and feathers of petrel Daption capense, bones and fur of seal Mirounga leonina, algae Himantothallus grandifolius, Desmarestia anceps and Cystosphaera jacquinotii, fish Notothenia corriceps, sea invertebrates Amphipoda, shells of limpet Nacella concina, lichen Usnea aurantiaco-atra, vascular plants Deschampsia antarctica and Colobanthus quitensis, fungi Omphalina pyxidata, moss Sanionia uncinata and soil. The results show a large variation in some activity concentrations. Samples from the marine environment had lower contamination levels than those from terrestrial ecosystems. The highest activity concentrations for all radionuclides were found in lichen and, to a lesser extent, in mosses, probably because lichens take up atmospheric pollutants and retain them. The only significant correlation (except for that expected between ²³⁸Pu and ^239+240Pu) was noted for moss and lichen samples between plutonium and ⁹⁰Sr. A tendency to a slow decrease with time seems to be occurring. Analyses of the activity ratios show varying fractionation between various radionuclides in different organisms. Algae were relatively more highly contaminated with plutonium and radiostrontium, and depleted with radiocesium. Feathers had the lowest plutonium concentrations. Radiostrontium and, to a lesser extent, Pu accumulated in bones. The present low intensity of fallout in Antarctic has a lower ²³⁸Pu/^239+240Pu activity ratio than that expected for global fallout.     

Salt-tolerant reed plants contain lower Na<Superscript>+</Superscript> and higher K<Superscript>+</Superscript> than salt-sensitive reed plants

Reed plants (Phragmites australis Trinius) grow not only in fresh and brackish water areas but also in arid and high salinity regions. Reed plants obtained from a riverside (Utsunomiya) were damaged by 257 mM NaCl, whereas desert plants (Nanpi) were not. When the plants were grown under salt stress, the shoots of the Utsunomiya plants contained high levels of sodium and low levels of potassium, whereas the upper part of the Nanpi plants contained low levels of sodium and high levels of potassium. One month salt stress did not affect potassium contents in either Utsunomiya or Nanpi plants, but it did dramatically increase sodium contents only in the Utsunomiya plants. The ratio of K⁺ to Na⁺ was maintained at a high level in the upper parts of the Nanpi plants, whereas the ratio markedly decreased in the Utsunomiya plants in the presence of NaCl. Accumulation of Na⁺ in the roots and Na⁺ efflux from the roots were greater in the Nanpi plants than in the Utsunomiya plants. These results suggest that the salt tolerance mechanisms of Nanpi reed plants include an improved ability to take up K⁺ to prevent an influx of Na⁺ and an improved ability to exclude Na⁺ from the roots.     

The Na<Superscript>+</Superscript>-translocating ATPase in the plasma membrane of the marine microalga<Emphasis Type="Italic"> Tetraselmis viridis</Emphasis> catalyzes Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> exchange

Our previous investigations have established that Na⁺ translocation across the Tetraselmis viridis plasma membrane (PM) mediated by the primary ATP-driven Na⁺-pump, Na⁺-ATPase, is accompanied by H⁺ counter-transport [Y.V. Balnokin et al. (1999) FEBS Lett 462:402–406]. The hypothesis that the Na⁺-ATPase of T. viridis operates as an Na⁺/H⁺ exchanger is tested in the present work. The study of Na⁺ and H⁺ transport in PM vesicles isolated from T. viridis demonstrated that the membrane-permeant anion NO₃^– caused (i) an increase in ATP-driven Na⁺ uptake by the vesicles, (ii) an increase in (Na⁺+ATP)-dependent vesicle lumen alkalization resulting from H⁺ efflux out of the vesicles and (iii) dissipation of electrical potential, , generated across the vesicle membrane by the Na⁺-ATPase. The (Na⁺+ATP)-dependent lumen alkalization was not significantly affected by valinomycin, addition of which in the presence of K⁺ abolished at the vesicle membrane. The fact that the Na⁺-ATPase-mediated alkalization of the vesicle lumen is sustained in the absence of the transmembrane is consistent with a primary role of the Na⁺-ATPase in driving H⁺ outside the vesicles. The findings allowed us to conclude that the Na⁺-ATPase of T. viridis directly performs an exchange of Na⁺ for H⁺. Since the Na⁺-ATPase generates electric potential across the vesicle membrane, the transport stoichiometry is mNa⁺/nH⁺, where m>n.Abbreviations BTP Bis-Tris-Propane, 1,3-bis[tris(hydroxymethyl)methylamino]-propane - CCCP Carbonyl cyanide m-chlorophenylhydrazone - DTT Dithiothreitol - NCDC 2-Nitro-4-carboxyphenyl N,N-diphenylcarbamate - PMSF Phenylmethylsulfonyl fluoride - PM Plasma membrane     

Stimulation of Transepithelial Na<Superscript>+</Superscript> Current by Extracellular Gd<Superscript>3+</Superscript> in <Emphasis Type="Italic">Xenopus laevis</Emphasis> Alveolar Epithelium

In the present study we investigated the effect of extracellular gadolinium on amiloride-sensitive Na⁺ current across Xenopus alveolar epithelium by Ussing chamber experiments and studied its direct effect on epithelial Na⁺ channels with the patch-clamp method. As observed in various epithelia, the short-circuit current (I _sc) and the amiloride-sensitive Na⁺ current (I _ami) across Xenopus alveolar epithelium was downregulated by high apical Na⁺ concentrations. Apical application of gadolinium (Gd³⁺) increased I _sc in a dose-dependent manner (EC ₅₀ = 23.5 µM). The effect of Gd³⁺ was sensitive to amiloride, which indicated the amiloride-sensitive transcellular Na⁺ transport to be upregulated. Benz-imidazolyl-guanidin (BIG) and p-hydroxy-mercuribenzonic-acid (PHMB) probably release apical Na⁺ channels from Na⁺-dependent autoregulating mechanisms. BIG did not stimulate transepithelial Na⁺ currents across Xenopus lung epithelium but, interestingly, it prevented the stimulating effect of Gd³⁺ on transepithelial Na⁺ transport. PHMB increased I _sc and this stimulation was similar to the effect of Gd³⁺. Co-application of PHMB and Gd³⁺ had no additive effects on I _sc. In cell-attached patches on Xenopus oocytes extracellular Gd³⁺ increased the open probability (NP _o) of Xenopus epithelial sodium channels (ENaC) from 0.72 to 1.79 and decreased the single-channel conductance from 5.5 to 4.6 pS. Our data indicate that Xenopus alveolar epithelium exhibits Na⁺-dependent non-hormonal control of transepithelial Na⁺ transport and that the earth metal gadolinium interferes with these mechanisms. The patch-clamp experiments indicate that Gd³⁺ directly modulates the activity of ENaCs.     

Involvement of Long-Distance Na<Superscript>+</Superscript> Transport in Maintaining Water Potential Gradient in the Medium-Root-Leaf System of a Halophyte <Emphasis Type="Italic">Suaeda altissima</Emphasis>

The aim of this study was to determine the range of NaCl concentrations in the nutrient solution that allow Suaeda altissima (L.) Pall., a salt-accumulating halophyte, to maintain the upward gradient of water potential in the “medium-root-leaf” system. We evaluated the contribution of Na⁺ ions in the formation of water potential gradient and demonstrated that Na⁺ loading into the xylem is involved in this process. Plants were grown in water culture at NaCl concentrations ranging from zero to 1 M. The water potential of leaf and root cells was measured with the method of isopiestic thermocouple psychrometry. When NaCl concentration in the growth medium was raised in the range of 0–500 mM (the medium water potential was lowered accordingly), the root and leaf cells of S. altissima decreased their water potential, thus promoting the maintenance of the upward water potential gradient in the medium-root-leaf system. Growing S. altissima at NaCl concentrations f 750 mM and 1 M disordered water homeostasis and abolished the upward gradient of water potential between roots and leaves. At NaCl concentrations of 0–250 mM, the detached roots of S. altissima were capable of producing the xylem exudate. The concentration of Na⁺ in the exudate was 1.3 to 1.6 times higher than in the nutrient medium; the exudate pH was acidic and was lowered from 5.5 to 4.5 with the rise in the salt concentration. The results indicate that the long-distance Na⁺ transport and, especially, the mechanism of Na⁺ loading into the xylem play a substantial role in the formation of water potential gradient in S. altissima. The accumulation of Na⁺ in the xylem and acidic pH values of the xylem sap suggest that Na⁺ loading into the xylem is carried out by the Na⁺/H⁺ antiporter of the plasma membrane in parenchymal cells of the root stele.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 549–557.Original Russian Text Copyright © 2005 by Balnokin, Kotov, Myasoedov, Khailova, Kurkova, Lun’kov, Kotova.     

<Superscript>65</Superscript>Zn<Superscript>2+</Superscript> transport by lobster hepato-pancreatic baso-lateral membrane vesicles

The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether ⁶⁵Zn²⁺ transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10–15 s and approached equilibrium by 120 s. In the absence of sodium, ⁶⁵Zn²⁺ influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 M ATP (increase in K_m and J_max) and inhibited by the simultaneous presence of 150 mol l^–1 ATP+250 mol l^–1 vanadate (decrease in both K_m and J_max). In the absence of ATP, ⁶⁵Zn²⁺ influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l^–1) and exhibited a Hill Coefficient of 4.03±1.14, consistent with the exchange of 3 Na⁺/1Zn²⁺. Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle ⁶⁵Zn²⁺ influx by both the ATP-dependent (K_i=205 nmol l^–1 Ca²⁺) and sodium-dependent (K_i=2.47 mol l^–1 Ca²⁺) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.Communicated by: I.D. Hume     

K<Superscript>+</Superscript> transport in the caterpillar intestine epithelium: role of osmolytes for the K<Superscript>+</Superscript>-secretory capacity of the tobacco hornworm midgut

The midgut of the tobacco hornworm, Manduca sexta, actively secretes potassium ions. This can be measured as short-circuit current (I_sc) with the midgut mounted in an Ussing chamber and superfused with a high-K⁺ saline containing as its major osmolyte 166 mM sucrose. Iso-osmotic substitution of sucrose by non-metabolisable compounds (mannitol, urea, NaCl and the polyethylene glycols 200, 400 and 600) led to a dramatic, though reversible, drop in the current. Acarbose, a specific inhibitor of invertase (sucrase) in vertebrates and insects, had no detectable influence on I_sc. Unexpectedly, after replacing sucrose iso-osmotically with the saccharides glucose, fructose, trehalose or raffinose, the K⁺ current could no longer be supported. However, all osmolytes smaller than sucrose (except for NaCl), metabolisable or not, initiated an immediate, quite uniform but transient, increase in I_sc by about 20%, before its eventual decline far below the control value. Hypo-osmotic treatment by omission of sucrose also transiently increased the K⁺ current. Small osmolytes substituted for sucrose caused no transient I_sc stimulation when the epithelium had been challenged before with hypo-osmolarity; however, the eventual decline in I_sc could not be prevented. Our data seem inconsistent with a role of sucrose as energiser or simple osmolyte. Rather, we discuss here its possible role as analogous to that of sucrose in lower eukaryotes or plants, as an extra- and/or intracellular compatible osmolyte that stabilises structure and/or function of the proteins implicated in K⁺ transport.Communicated by G. Heldmaier     

New isoform HvNHX3 of vacuolar Na<Superscript>+</Superscript>/H<Superscript>+</Superscript>-antiporter in barley: Expression and immunolocalization

The gene HvNHX3 encoding a new isoform of vacuolar Na⁺/H⁺-antiporter was identified in barley. This gene is expressed in roots and leaves of barley seedlings, and it encodes a protein consisting of 541 amino acid residues with pre-dicted molecular weight 59.7 kDa. It was found that by its amino acid sequence HvNHX3 is closest to the Na⁺/H⁺-antiporter HbNHX1 of wild type from Hordeum brevisibulatum that grows on salt-marsh (solonchak) soils (95% homology). The expression of HvNHX3 during salt stress is increased several-fold in roots and leaves of barley seedlings. At the same time, the amount of HvNHX3 protein in roots does not change, but in leaves it increases significantly. It was shown using HvNHX3 immunolocalization in roots that this protein is present in all tissues, but in control plants it was clustered and in experimental plants after salt stress it was visualized as small granules. It has been proposed that HvNHX3 is converted into active form during declusterization. The conversion of HvNHX3 into its active form along with its quantitative increase in leaves during salt stress activates Na⁺/H⁺-exchange across the vacuolar membrane and Na⁺ release from cytoplasm, and, as a consequence, an increase of salt stress tolerance.     

海桑次生木质部导管解剖特征与土壤理化因子年内动态变化的关系研究

为揭示海桑次生木质部导管解剖特征随土壤理化因子年内动态变动而变化的适应机制,该研究利用海桑具有生长轮的特点,通过显微技术界定了海桑采样枝条一年内10个不同连续时间段形成的新"生长层"(新形成的次生木质部),观测了10个不同连续时间段新"生长层"的导管解剖特征,并对10个新"生长层"形成阶段所对应的土壤理化因子数量特征进行了测定,用逐步回归法分析了10个不同连续时间段海桑新"生长层"管孔数量解剖特征与对应土壤理化因子数量特征之间的关系。结果显示:(1)10个不同连续时间段海桑形成新"生长层"管孔数量特征指标,除相邻管孔间接触壁长占比无显著差异外,其他8项指标包括管孔径向直径、管孔弦向直径、导管壁厚、导管长度、管孔密度、单孔率、导管聚合度和相邻管孔间接触壁长等均具有显著差异(P0.05);多重比较显示,10个不同连续时间段海桑形成新"生长层"管孔数量特征8项指标具不同程度的变动。(2)海桑新"生长层"形成阶段(10个不同连续时间段)土壤理化因子,包括土壤有机质含量、土壤全氮含量、土壤全磷含量、土壤pH值和土壤全盐量等5项指标均具有显著差异(P0.05);多重比较显示,海桑新"生长层"形成阶段(10个不同连续时间段)土壤理化因子指标均具有不同程度变动。(3)10个不同连续时间段海桑形成新"生长层"的管孔数量解剖特征,与所对应新"生长层"形成阶段土壤理化因子数量特征的逐步回归分析表明,随着土壤全盐含量的升高,海桑导管弦向直径和导管聚合度同时呈显著增大趋势(P0.05)。研究表明,海桑在一年内不同连续时间段,随土壤全盐量增加,土壤渗透势将增大,水分在次生木质部导管中输导的安全性将下降,而海桑导管分子随一年内不同连续时间段土壤全盐量的增加呈增大趋势,根据木材生态解剖学的观点,水分输导的安全性将进一步降低,但导管聚合度随一年内不同连续时间段土壤全盐量的增加而增大,具有增进水分输导安全性的作用,这可能是海桑对土壤盐含量变化的生态适应策略。     

Transport of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> by an antiporter-related subunit from the <Emphasis Type="Italic">Escherichia coli </Emphasis>NADH dehydrogenase I produced in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

The NADH dehydrogenase I from Escherichia coli is a bacterial homolog of the mitochondrial complex I which translocates Na⁺ rather than H⁺. To elucidate the mechanism of Na⁺ transport, the C-terminally truncated NuoL subunit (NuoL_N) which is related to Na⁺/H⁺ antiporters was expressed as a protein A fusion protein (ProtA–NuoL_N) in the yeast Saccharomyces cerevisiae which lacks an endogenous complex I. The fusion protein inserted into membranes from the endoplasmatic reticulum (ER), as confirmed by differential centrifugation and Western analysis. Membrane vesicles containing ProtA–NuoL_N catalyzed the uptake of Na⁺ and K⁺ at rates which were significantly higher than uptake by the control vesicles under identical conditions, demonstrating that ProtA–NuoL_N translocated Na⁺ and K⁺ independently from other complex I subunits. Na⁺ transport by ProtA–NuoL_N was inhibited by EIPA (5-(N-ethyl-N-isopropyl)-amiloride) which specifically reacts with Na⁺/H⁺ antiporters. The cation selectivity and function of the NuoL subunit as a transporter module of the NADH dehydrogenase complex is discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of gibberellic acid on <Superscript>14</Superscript>CO<Subscript>2</Subscript> metabolism,growth, and production of alkaloids in <Emphasis Type="Italic">Catharanthus roseus</Emphasis>

Changes in growth parameters, carbon assimilation efficiency, and utilization of ¹⁴CO₂ assimilate into alkaloids in plant parts were investigated at whole plant level by treatment of Catharanthus roseus with gibberellic acid (GA). Application of GA (1 000 g m⁻³) resulted in changes in leaf morphology, increase in stem elongation, leaf and internode length, plant height, and decrease in biomass content. Phenotypic changes were accompanied by decrease in contents of chlorophylls and in photosynthetic capacity. GA application resulted in higher % of total alkaloids accumulated in leaf, stem, and root. GA treatment produced negative phenotypic response in total biomass production but positive response in content of total alkaloids in leaf, stem, and roots. ¹⁴C assimilate partitioning revealed that ¹⁴C distribution in leaf, stem, and root of treated plants was higher than in untreated and variations were observed in contents of metabolites as sugars, amino acids, and organic acids. Capacity to utilize current fixed ¹⁴C derived assimilates for alkaloid production was high in leaves but low in roots of treated plants despite higher content of ¹⁴C metabolites such as sugars, amino acids, and organic acids. In spite of higher availability of metabolites, their utilization into alkaloid production is low in GA-treated roots.     

Increased Polyamines Conjugated to Tonoplast Vesicles Correlate with Maintenance of the H<Superscript>+</Superscript>-ATPase and H<Superscript>+</Superscript>-PPase Activities and Enhanced Osmotic Stress Tolerance in Wheat

The effects of osmotic stress on H⁺-ATPase and H⁺-PPase activities and the levels of covalently conjugated polyamines (CC-PAs) and noncovalently conjugated polyamines (NCC-PAs) were investigated using tonoplast vesicles isolated from the roots of wheat (Triticum aestivum L.) seedlings differing in drought-tolerance. The results showed that after polyethylene glycol (PEG) 6,000 (–0.55MPa) treatment for 7 days, seedling leaf relative water content (LRWC), relative dry weight increase rate (RDWIR) and root H⁺-ATPase and H⁺-PPase activities from the drought-sensitive cultivar Yangmai No. 9 decreased more markedly than those from the drought-tolerant cultivar Yumai No. 18. At the same time, the increase of the NCC-spermidine (NCC-Spd) and CC-putrescine (CC-Put) levels in root tonoplast vesicles from Yumai No. 18 was more obvious than that from Yangmai No. 9. Exogenous Spd treatment alleviated osmotic stress injury to Yangmai No. 9 seedlings, coupled with marked increases of tonoplast NCC-Spd levels and H⁺-ATPase and H⁺-PPase activities. Treatments with methylglyoxyl bis (guanyl hydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), and phenanthrolin, an inhibitor of transglutaminase (TGase), significantly inhibited the osmotically induced increases of NCC-Spd and CC-Put levels, respectively, in root tonoplast vesicles from Yumai No. 18 seedlings. Both MGBG and phenanthrolin treatments markedly promoted osmotically induced decreases of tonoplast H⁺-ATPase and H⁺-PPase activities and osmotic stress tolerance of seedlings of this cultivar. These results suggest that the NCC-Spd and CC-Put present in tonoplast vesicles isolated from wheat seedling roots might enhance the adaptation of seedlings to osmotic stress via maintenance of tonoplast H⁺-ATPase and H⁺-PPase activities.     

Use of foliar Ca/Sr discrimination and <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and ⁸⁷Sr/⁸⁶Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the ⁸⁷Sr/⁸⁶Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios to trace Ca sources to plants.     

Sulfatide and Na<Superscript>+</Superscript>-K<Superscript>+</Superscript>-ATPase: A Salinity-sensitive Relationship in the Gill Basolateral Membrane of Rainbow Trout

We investigated the effect of salinity on the relationship between Na⁺-K⁺-ATPase and sulfogalactosyl ceramide (SGC) in the basolateral membrane of rainbow trout (Oncorhynchus mykiss) gill epithelium. SGC has been implicated as a cofactor in Na⁺-K⁺-ATPase activity, especially in Na⁺-K⁺-ATPase rich tissues. However, whole-tissue studies have questioned this role in the fish gill. We re-examined SGC cofactor function from a gill basolateral membrane perspective. Nine SGC fatty acid species were quantified by tandem mass spectrometry (MS/MS) and related to Na⁺-K⁺-ATPase activity in trout acclimated to freshwater or brackish water (20 ppt). While Na⁺-K⁺-ATPase activity increased, the total concentration and relative proportion of SGC isoforms remained constant between salinities. However, we noted a negative correlation between SGC concentration and Na⁺-K⁺-ATPase activity in fish exposed to brackish water, whereas no correlation existed in fish acclimated to freshwater. Differential Na⁺-K⁺-ATPase/SGC sensitivity is discussed in relation to enzyme isoform switching, the SGC cofactor site model and saltwater adaptation.This revised version was published online in June 2005 with a corrected cover date.     

Glutamatergic hypothesis of schizophrenia: involvement of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-dependent glutamate transport

Summary Hypothetical model based on deficient glutamatergic neurotransmission caused by hyperactive glutamate transport in astrocytes surrounding excitatory synapses in the prefrontal cortex is examined in relation to the aetiology of schizophrenia. The model is consistent with actions of neuroleptics, such as clozapine, in animal experiments and it is strongly supported by recent findings of increased expression of glutamate transporter GLT in prefrontal cortex of patients with schizophrenia. It is proposed that mechanisms regulating glutamate transport be investigated as potential targets for novel classes of neuroactive compounds with neuroleptic characteristics. Development of new efficient techniques designed specifically for the purpose of studying rapid activity-dependent translocation of glutamate transporters and associated molecules such as Na⁺, K⁺-ATPase is essential and should be encouraged.     

Design and development of a simple laboratory model to detect <Superscript>15</Superscript>N enrichment in cyanobacterial biomass and extra cellular ammonia using <Superscript>15</Superscript>N gas

A laboratory scale working model that could detect the ¹⁵N enrichment in cyanobacterial biomass and extracellular ammonia, using ¹⁵N gas under in vitro conditions was designed and fabricated. Using the model, ¹⁵N enrichment of 0.48% atom excess was detected in the cyanobacterial biomass on the 30 d after inoculation. The ¹⁵N enrichment increased linearly in the extracellular ammoniacal fraction from the 20 d onward. The model would prove to be a useful tool to quantify the extent of ¹⁵N enrichment under in vitro conditions using ¹⁵N gas.     

NhaK,a novel monovalent cation/H<Superscript>+</Superscript> antiporter of <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Four Na⁺/H⁺ antiporters, Mrp, TetA(L), NhaC, and MleN have so far been described in Bacillus subtilis 168. We identified an additional Na⁺/H⁺ antiporter, YvgP, from B. subtilis that exhibits homology to the cation: proton antiporter-1 (CPA-1) family. The yvgP-dependent complementation observed in a Na⁺(Ca²⁺)/H⁺ antiporter-defective Escherichia coli mutant (KNabc) suggested that YvgP effluxed Na⁺ and Li⁺. In addition, effects of yvgP expression on a K⁺ uptake-defective mutant of E. coli indicated that YvgP also supported K⁺ efflux. In a fluorescence-based assay of everted membrane vesicles prepared from E. coli KNabc transformants, YvgP-dependent Na⁺ (K⁺, Li⁺, Rb⁺)/H⁺ antiport activity was demonstrated. Na⁺ (K⁺, Li⁺)/H⁺ activity was higher at pH 8.5 than at pH 7.5. Mg²⁺, Ca²⁺ and Mn²⁺ did not serve as substrates but they inhibited YvgP antiport activities. Studies of yvgP expression in B. subtilis, using a reporter gene fusion, showed a significant constitutive level of expression that was highest in stationary phase, increasing as stationary phase progressed. In addition, the expression level was significantly increased in the presence of added K⁺ and Na⁺.     

Simultaneous <Superscript>1</Superscript>H- or <Superscript>2</Superscript>H-, <Superscript>15</Superscript>N- and multiple-band-selective <Superscript>13</Superscript>C-decoupling during acquisition in <Superscript>13</Superscript>C-detected experiments with proteins and oligonucleotides

Significant resolution improvement in ¹³C,¹³C-TOCSY spectra of uniformly deuterated and ¹³C, ¹⁵N-labeled protein and ¹³C,¹⁵N-labeled RNA samples is achieved by introduction of multiple-band-selective ¹³C-homodecoupling applied simultaneously with ¹H- or ²H- and ¹⁵N-decoupling at all stages of multidimensional experiments including signal acquisition period. The application of single, double or triple band-selective ¹³C-decoupling in 2D-[¹³C,¹³C]-TOCSY experiments during acquisition strongly simplifies the homonuclear splitting pattern. The technical aspects of complex multiple-band homonuclear decoupling and hardware requirements are discussed. The use of this technique (i) facilitates the resonance assignment process as it reduces signal overlap in homonuclear ¹³C-spectra and (ii) possibly improves the signal-to-noise ratio through multiplet collapse. It can be applied in any ¹³C-detected experiment.