Effects of furosemide on neural mechanisms in aplysia

The effects of furosemide on action potentials and responses to several neurotransmitters have been studied in the neurons of Aplysia. Furosemide (10^?7 and 10^?3M) does not visibly affect the normal action potential in R15 neurons. However, when TTX (30μM) is used to block the sodium component in R15, the remaining spike (presumably the calcium component) is increased in amplitude in the presence of furosemide. Furosemide also alters transmitter-induced conductances. Furosemide greatly reduces the amplitude and shifts, in a depolarizing direction, the reversal potential of chloride-dependent responses to γ-aminobutyric acid (GABA) and acetylcholine (ACh). This suggests that furosemide both blocks the chloride channel and inhibits a chloride pump. ACh-induced sodium responses were also reduced by furosemide but to a lesser extent than chloride responses. The potassium response to ACh and a voltage-dependent calcium response to serotonin were not altered. These results indicate that furosemide could alter synaptic responses both presynaptically by enhancement of calcium flux during the action potential and postsynaptically by blockade of chloride and sodium conductances.     

Evidence for a Na+/K+/Cl− cotransport system in basolateral membrane vesicles from the rabbit parotid

Summary Sodium (²²Na) transport was studied in a basolateral membrane vesicle preparation from rabbit parotid. Sodium uptake was markedly dependent on the presence of both K⁺ and Cl^– in the extravesicular medium, being reduced 5 times when K⁺ was replaced by a nonphysiologic cation and 10 times when Cl^– was replaced by a nonphysiologic anion. Sodium uptake was stimulated by gradients of either K⁺ or Cl^– (relative to nongradient conditions) and could be driven against a sodium concentration gradient by a KCl gradient. No effect of membrane potentials on KCl-dependent sodium flux could be detected, indicating that this is an electroneutral process. A KCl-dependent component of sodium flux could also be demonstrated under equuilibrium exchange conditions, indicating a direct effect of K⁺ and Cl^– on the sodium transport pathway. KCl-dependent sodium uptake exhibited a hyperbolic dependence on sodium concentration consistent with the existence of a single-transport system withK _m =3.2mm at 80mm KCl and 23°C. Furosemide inhibited this transporter withK _0.5=2×10^–4 m (23°C). When sodium uptake was measured as a function of potassium and chloride concentrations a hyperbolic dependence on [K] (Hill coefficient =1.31±0.07) were observed, consistent with a Na/K/Cl stoichiometry of 112. Taken together these data provide strong evidence for the electroneutral coupling of sodium and KCl movements in this preparation and strongly support the hypothesis that a Na⁺/K⁺/Cl^– cotransport system thought to be associated with transepithelial chloride and water movements in many exocrine glands is present in the parotid acinar basolateral membrane.     

Comparative sensitivity of 'Prior Lisbon' lemon and 'Valencia' orange trees to foliar sodium and chloride concentrations

Abstract While citrus rootstocks differ in capacity for sodium and chloride ion exclusion, citrus scion species also vary in foliar sensitivity to NaCl salinisation. Of two common scions, ‘Lisbon’ lemon appears more sensitive, whereas ‘Valencia’ orange in less sensitive to leaf salt. In an attempt to explain this difference. ‘Valencia’ orange (Citrus sinensis [L.] Osbeck) and ‘Prior Lisbon’ lemon (Citrus limon [L.] Burm. F.) were budded to rootstocks known to differ in their ability to exclude sodium ions viz, the strong excluder Trifoliata (Poncirus trifoliata [L.] Raf.), and the weaker excluder Troyer citrange (C. sinensis×P. trifoliata); neither rootstock shows strong exclusion of chloride ions. Budded trees were held under a photosynthetic photon flux density of 450 μmol m ² S ¹ and watered with nutrient solution containing either 0 or 50 mol m ³ NaCl. Growth and photosynthetic responses were measured over 58 d following onset of salinization: salinity effects on leaf gas exchange were studied in relation to changes in leaf water status, compatible solutes and foliar content of sodium and chloride ions, over that same period. Once root-zone salinization began to influence leaf solutes (day 30 onwards), lemon showed a steeper increase in leaf chloride than occurred for orange. Although rootstock differences were without effect on this ingress of chloride ions for either scion, sodium ions were excluded from both scions to a larger extent by Trifoliata than by Troyer citrange. Carbon dioxide assimilation of scion foliage was reduced earlier and to a much larger extent by rootzone salinization in lemon than in orange. Furthermore, comparisons of CO₂ assimilation in relation to leaf tissue solutes between scions (on either rootstock) showed stronger responses for both sodium and chloride ions in lemon than in orange. Faster ingress of chloride into lemon leaves was identified as the crucial factor which predisposed towards expression of that contrast between scions. Although contrasts between scions in photosynthetic responses to salinization matched a faster ingress of chloride into lemon than into orange leaves, the sharper photosynthetic response of ‘Prior Lisbon’ lemon to salinity was not solely attributable to higher concentrations of chloride ions (cell sap basis). A difference between species in subcellular compartmentation of the chloride ion under saline conditions was invoked.     

The ionic regulation of action potentials in the axon of a stretch receptor neuron of the stick insect (Carausius morosus)

Summary The ionic requirements for the action potentials recorded from the axon of the dorsal longitudinal stretch receptor inCarausius morosus have been studied using extracellular electrodes.In the intact preparation prolonged exposure to sodium-free, calcium-free, or magnesium-free salines produces no observable change in the amplitude of action potentials. Similarly, tetrodotoxin (1×10^–6 M) and cobaltous chloride (1×10^–2 M) are both ineffective in blocking the action potentials.In preparations in which the ionic barrier has been disrupted by removal of the nerve sheath the action potentials show sodium dependence. They are sustained in high sodium salines (150 mM) but are reversibly abolished in sodium-free salines. They are also reversibly abolished in 1×10^–6 M TTX, but unaffected by calcium-free or magnesium-free salines, or by cobaltous chloride (1×10^–2 M).It is concluded that the action currents in the axon of the stretch receptor are carried by sodium ions.     

Enhancing lipid production of the marine diatom Chaetoceros gracilis: synergistic interactions of sodium chloride and silicon

Silicon deficiency is a lipid-promoting stress for many oleaginous diatoms. Literature reports suggest that reduced salinity in seawater, a primary component of which is sodium chloride, may inhibit metabolism of silicon in marine diatoms. We hypothesized that lowering sodium chloride below ocean levels may thus be effective in creating silicon stress and enhancing lipid productivity. We examined the interacting effects of silicon supply (0.05, 0.1, 0.2, and 0.8 mM) and sodium chloride concentration (50, 100, and 400 mM) on growth and lipid production in Chaetoceros gracilis. This was done in batch culture to facilitate the application of severe stress. Low levels of either sodium chloride or silicon resulted in at least 50 % increases in lipid content. The synergy of simultaneous, moderate sodium chloride and silicon stress resulted in lipid content up to 73 % of dry mass and lipid productivity of 1.7 g m^?2 day^?1; with a daily integrated photosynthetic photon flux of 17.3 mol photons m^?2 day^?1, the efficiency of lipid synthesis was thus 0.1 g mol^?1 of photons. Decreased silicon also resulted in a 5 % shift in lipid chain length from C18 to C16 fatty acids. We observed a strong sodium chloride/silicon interaction on total and ash-free dry mass densities that arose because low sodium chloride concentrations were inhibitory to growth, but the inhibition was overcome with excessive silicon supply. This observation suggests that low levels of sodium chloride may have affected metabolism of silicon. The findings of this study can be used to enhance lipid production in oleaginous marine diatoms.     

Prediction of proton exchange and bacterial growth on various substrates using constraint-based modeling approach

Proton exchange between cells and medium is one of the most important factors affecting culture pH, and hence its prediction is advantageous. In this research, proton exchange flux across the cell membrane was predicted using a genome-scale model. Calculated proton exchange flux was then exploited as a criterion to predict the trends and intensities of pH changes in cultures of Bacillus subtilis containing various C-sources, i.e. glucose, sucrose, glycerol, lactate, and citrate, as well as N-sources, i.e. ammonium chloride, sodium nitrate, urea, and histidine. The results showed that glucose, sucrose, and glycerol lowered culture pH as compared to citrate and lactate, which raised it. With regard to N-sources, the model predicted that ammonium chloride lowered culture pH while other sources raised pH. Furthermore, maximum theoretical biomass yield using the various C&N-sources was calculated, and sensitivity of microbial growth to proton exchange flux was investigated using robustness analysis to identify the effect of pH on growth of B. subtilis using different substrates. Finally, the effect of ammonium nitrate, a widely used nitrogen source, on growth of B. subtilis was studied. Experimental data obtained by cultivation of B. subtilis DSM 3256 on mineral salt media containing various C&N-sources were used to confirm model predictions. Model predictions were in good agreement with the experimental results for all of the examined C-sources as well as ammonium chloride and sodium nitrate as N-sources. However, the predictions for the N-sources urea and histidine showed deviations, possibly because these two compounds serve as both C&N-sources.     

Can soil Chytridiomycota survive and grow in different osmotic potentials?

Twenty isolates from soil in the orders Spizellomycetales, Blastocladiales and Chytridiales (Chytridiomycota) grew on complex solid media supplemented with 10 g l⁻¹ sodium chloride. In a synthetic liquid medium, 4.4 g l⁻¹ sodium chloride strongly inhibited growth in three of the five isolates, possibly because of the effect of the ions or osmolarity of the solution. The maximum concentration for growth in synthetic liquid medium with different osmotic potentials using polyethylene glycol (PEG) varied considerably amongst the isolates. Three patterns of growth with increasing concentrations of PEG were evident among isolates within the genus Rhizophydium. Up to the concentration where growth ceased, the dry weight of each isolate either decreased, remained constant, or in one case, increased. Most of the fungi survived when incubated at room temperature for 7 d in complex liquid media supplemented with 35 g l⁻¹ sodium chloride or 300 g l⁻¹ PEG. These data indicate that soil Chytridiomycota can survive various osmotic potentials that may occur during the wetting and drying phases in soils.     

Steady State Sodium and Rubidium Effluxes in Pisum sativum Roots

Steady state effluxes of potassium and sodium ions were measured on Pisum sativum var. Alaska root segments excised from seedlings which had grown in a nutrient solution containing the major inorganic ions and either ⁸⁶Rb as a tracer for K or ²²Na as a tracer for Na. Fluxes appeared to be from 2 cellular compartments, a small compartment with a high flux rate and a larger compartment with a slow flux rate. Cell wall exchange fluxes are believed to have been negligible. Efflux rates for 11.3% and 88.7% of cellular potassium ions were 6 × 10⁻⁷ and 1.32 × 10⁻⁷ respectively; rates for 33.7% and 66.3% of cellular sodium ions were 1.48 × 10⁻⁷ and 3.83 × 10⁻⁸ respectively, (equivalents per gram fr wt per hr). The sodium flux measurements, with previous measurements of ionic concentrations and transmembrane potentials, support the theory that sodium is transported actively from Pisum roots.     

Dependence of water movement on sodium transport in kidney proximal tubule: A microperfusion study substituting lithium for sodium

Summary The relationship between water and sodium movements through the mammalian proximal convoluted tubule was investigated by substituting lithium for sodium. Proximal convoluted rat Kidney tubules were perfusedin vivo with a Ringer solution containing 107 meq/liter lithium and 42 meq/liter sodium. Several micropunctures were made along the same nephron, and [³H] inulin, [¹⁴C] glucose,²²Na, osmolality, Na, Mg and Cl were determined on each sample. Measurements of²²Na showed that sodium and lithium diffusion rates were practically identical throughout the entire epithelium. A one- for-one exchange of sodium for lithium induced a negative trans-epithelial net flux of Na from plasma to lumen. However, despite this negative flux, a positive net water movement was measured from lumen to plasma. This movement was proportional both to glucose reabsorption and to the rise in the chloride concentration, two mechanisms known to be dependent on the trans-cellular movement of sodium. It was therefore concluded that the net water flux was a function of the unidirectional transcellular net flux of Na.Rabbit proximal convoluted tubules were perfusedin vitro with a solution containing 75 meq/liter Li and 75 meq/liter Na on both the luminal and peritubular sides. Under these conditions, the water reabsorption rate dropped to half its control value. Water movement was therefore a function of the external sodium concentration, which in turn probably regulates the intracellular Na concentration.     

Mitochondria-rich cells in Antarctic fish gills

We used transmission and scanning electron microscopy and an antibody to the inner mitochondrial membrane to study the presence and localisation of mitochondria-rich cells in the gills of two Antarctic fishes, Chionodraco hamatus (Channichthyidae) and Trematomus bernacchii (Nototheniidae). The general morphology of the gills in the two species was slightly different: in T. bernacchii the filament and secondary lamellae were short and thicker, and mitochondria-rich cells were less numerous than in C. hamatus. In the two species the mitochondria-rich cells, distributed in the secondary and primary epithelium, were of the same morphological type, similar to the α-chloride cells of temperate seawater teleosts. The study was carried out to compare the mitochondria-rich cells of Antarctic fishes to the chloride cells of temperate marine teleosts. Immunolocalisation, using a specific antibody to the α-subunit of Na⁺/K⁺-ATPase, was observed in numerous epithelial cells in the interlamellar epithelium and on the secondary lamellae, suggesting an active sodium chloride secretion. Accepted: 16 October 1999     

Metabolic flux analysis of Shewanella spp. reveals evolutionary robustness in central carbon metabolism

Shewanella spp. are a group of facultative anaerobic bacteria widely distributed in marine and freshwater environments. In this study, we profiled the central metabolic fluxes of eight recently sequenced Shewanella species grown under the same condition in minimal medium with [3‐¹³C] lactate. Although the tested Shewanella species had slightly different growth rates (0.23–0.29 h^?1) and produced different amounts of acetate and pyruvate during early exponential growth (pseudo‐steady state), the relative intracellular metabolic flux distributions were remarkably similar. This result indicates that Shewanella species share similar regulation in regard to central carbon metabolic fluxes under steady growth conditions: the maintenance of metabolic robustness is not only evident in a single species under genetic perturbations (Fischer and Sauer, 2005; Nat Genet 37(6):636–640), but also observed through evolutionary related microbial species. This remarkable conservation of relative flux profiles through phylogenetic differences prompts us to introduce the concept of metabotype as an alternative scheme to classify microbial fluxomics. On the other hand, Shewanella spp. display flexibility in the relative flux profiles when switching their metabolism from consuming lactate to consuming pyruvate and acetate. Biotechnol. Bioeng. 2009;102: 1161–1169. © 2008 Wiley Periodicals, Inc.     

Experimental design of a simple medium for the bioluminescence of Aliivibrio fischeri and mathematical modelling for growth estimation

Increasing numbers of studies are using Aliivibrio fischeri (A. fischeri), a marine bioluminescent bacterium as a model, however the culture medium used for its growth are complex and expensive. The objectives of this study were: (1) to evaluate the effect of yeast extract, tryptone, and NaCl to select a simple and inexpensive culture medium suitable for A. fischeri growth and bioluminescence induction; and (2) to compare the performance of mathematical models to predict the growth of A. fischeri. A fractional factorial design was performed to evaluate the effect of yeast extract, tryptone, and sodium chloride on the luminescence of A. fischeri. The result showed that sodium chloride is the most important factor, congruent with its inducer role in bioluminescence. The best medium for bioluminescence induction was selected through an optimization plot, this medium is inexpensive, and generates the same luminescence as commercial formulations. The estimation of A. fischeri growth at OD₆₀₀ measurement was statistically analyzed. All evaluated models fitted the data adequately (r²  > 0.96). The nonlinear models Gompertz, Richards and logistic provided a lower variation and a better fit of the growth estimation (r² >0.99), showing that these mathematical models can be used for the accurate growth prediction of A. fischeri.     

THE EFFECTS OF SODIUM CHLORIDE ON HIGHER PLANTS

(1) This review concentrates on the effect of sodium chloride on the growth of higher plants, being primarily concerned with relatively high concentrations i.e. 50 mmol 1^-1 and above, though something is also said about those instances when sodium acts as a micronutrient. Emphasis is placed on particular species or genera for which enough information is available to discuss possible mechanisms. (2) Trace amounts of sodium are required for the growth of plants using the C₄ pathway of carbon fixation and may also be important in plants with Crassulacean acid metabolism. (3) The increased growth of Beta vulgaris brought about by sodium chloride can in part be explained by a sparing effect on potassium. However, growth is still increased when sufficient potassium is available. Complementary studies with rubidium indicate that the hormone balance in the plant may be changed. Sodium chloride also increases the level of sucrose in storage roots and allows beet plants to withstand water stress more readily, possibly by increased turgor pressure. (4) Sodium chloride increases production of dry matter in C₄ species of Atriplex under conditions of low relative humidity because water loss is reduced and photo-synthesis hardly affected. (5) Succulence in many plants is stimulated by salinity. The essential basis of the phenomenon is an increased water potential gradient between the leaf and the external medium. In some instances, it is the accumulation of chloride which is important; in others it is the accumulation of cations, when potassium can be as effective as sodium. (6) Salinity reduces the final area achieved by growing leaves. Most of the studies have been made on Phaseolus vulgaris and an important early event is the reduction in the rate of expansion of the epidermal cells and this may be accompanied by a decrease in their number. Reduction of epidermal cell size is a result of water stress; sodium chloride may directly affect cell division, though water stress cannot be ruled out. Whether salinity brings about inhibition of cell division depends upon the calcium content of the medium – a high content is accompanied solely by a reduction in epidermal cell size. (7) Hormones, as yet unspecified, may play an important part in response of a growing leaf to salinity. However, there is no evidence that sodium chloride per se has an effect on hormone balance within the plant. So far, any measured changes in levels of specific hormones can be ascribed to the osmotic effects of the saline medium. (8) Two estimates by flux analysis of cytoplasmic concentration of sodium in plants growing in conditions of high salinity give a value of around 150 mmol 1^-1. There is no similar information for chloride. Other techniques (histochemistry and X-ray micro-probe analysis) give questionable information. (9) There is now extensive information to show that enzymes of halophytes (other than ATPases) do not differ significantly from those of other higher plants with respect to their sensitivity in vitro to sodium chloride. There is a need for further work with respect to the activity of enzymes in the presence of those metabolites which have the highest cytoplasmic concentration. (10) Sodium-stimulated ATPases have been isolated from plant cells but their distribution amongst higher plants is restricted. (11) There are a number of reports of changed metabolism brought about by saline treatments but it is not clear how far the effects of sodium chloride and water stress are confounded. (12) Sodium appears to increase the sucrose levels in sugar beet by an inhibitory effect on product starch-granule-bound ADP-glucose starch synthase. (13) Reversal of a sodium pump located at the plasmalemma might have an effect on cell turgor. (14) Sodium (like other monovalent cations) causes loss of materials from plant cells, possibly through an effect on carrier proteins; calcium prevents this from happening. Calcium also allows plants to grow better in saline conditions by a depression of sodium uptake by and transport within the plant. The properties and composition of the membranes of mesophytes and halophytes need to be compared. (15) A saline medium exerts a major effect on plant growth through water stress to which a halophyte must adapt. As well as this, the cytoplasmic concentration of sodium chloride must be kept lower than the total cellular concentration of the salt. Unless this happens, it is likely that enzymic activity will be reduced due, in some instances, to an unspecific effect of a high concentration of monovalent cations and/or chloride and in other instances to competition between sodium and other cations, specifically potassium, for activation sites on enzymes, e.g. pyruvate kinase. (16) Further work is required to separate the osmotic effects from the specific effect of sodium chloride after it has entered the plant. As well as this, it has become clear that more information is needed about the mineral nutrition of halophytes.     

Abiotic factors affecting the development of <Emphasis Type="Italic">Ulva</Emphasis> sp. (Ulvophyceae; Chlorophyta) in freshwater ecosystems

The influence of physicochemical factors on the development of Ulva species with distromatic tubular morphology was studied in three streams located in Poznan, Poland. The study evaluated key environmental factors that may influence the colonisation and growth of Ulva populations in freshwater systems. In total, nine environmental parameters were included: temperature, water depth, pH, oxygen (O₂), ammonium (NH₄ ⁺), nitrate (NO₃ ⁻), phosphate (PO₄ ³⁻), sodium chloride (NaCl) and total iron (Fe). Morphometric features of thalli (length and width, percentage of furcated and young thalli) and surface area of free-floating mats formed by the freshwater populations of Ulva were compared at all sites. Principal components analysis indicated the most important factors influencing Ulva development were sodium chloride concentrations and water depth. Two other key chemical factors affecting the freshwater form of Ulva were phosphate and nitrite concentrations. High concentrations of sodium chloride inhibited the development of Ulva, leading to a lower number of thalli in the Ulva mats. At the sites with stable and deeper water, the surface area of the mats was larger. Both phosphate and nitrite concentrations were positively correlated with an increase in the number of thalli in the mats and the thalli length.     

Fertilization environment of the non-copulating marine sculpin, Hemilepidotus gilberti

To clarify the extracellular environment for external fertilization in the non-copulating marine sculpin Hemilepidotus gilberti, sperm motility was measured in NaCl, KCl, mannitol solutions, seawater, and ovarian fluid. Spermatozoa of H. gilberti actively moved in seminal plasma the moment they were removed from the genital papilla. Spermatozoa showed higher motility in NaCl solution at osmolalities between 300–400 mOsmol kg^-1. In KCl and in mannitol solutions, spermatozoa actively moved at osmolalities between 500 and 800 mOsmol kg^-1, and at osmolality 300 mOsmol kg ^-1, respectively. The ovarian fluid was a transparent and viscous gelatinous material, rich in sodium with an osmolality of 340 mOsmol kg^-1. Sperm motility in the ovarian fluid lasted more than 90 min, which was six times longer than in seawater. This sperm motility under conditions isotonic to body fluid is similar to that of copulating marine sculpins rather than to other non-copulating marine fishes. In addition, eggs of H. gilberti could be fertilized in the ovarian fluid. This suggests that external fertilization takes place under physiological conditions similar to the internal conditions of the ovary provided by the ovarian fluid, which isolates the eggs from sea water for several hours after spawning. This manner of fertilization is thought to be one of the evolutionary pre-adaptations allowing copulation among marine sculpins.     

Fluxes of Na+, Rb+ and Cl- Ions in Excised Roots of Sugar Beet Seedlings

Uptake and fluxes of sodium, rubidium (instead of potassium), and chloride ions in segments of 3-week-old sugar beet roots were studied. Radioactive ²²Na, ⁸⁶Rb and ³⁶Cl were used for labelling of the ions. Compartmental analysis was used to obtain the fluxes and concentrations in the cell compartments. The passive or active character of the movements was examined by the Ussing-Teorell equation and compared with electropotential measurements. In the case of sodium, net flux was in the outward direction over both tonoplast and plasmalemma, but the active components were directed away from the cytoplasm. Potassium was close to equilibrium. Chloride was actively transported from the medium to the cytoplasm, and — contrary to observations in other systems — from the vacuole to the cytoplasm. This unusual situation may be caused by a loss of sugar, both by lowering the energy supply and by formation of organic acids.     

Morphology and ecology of Oblea rotunda (Diplopsalidaceae,Dinophyceae) from a new habitat: a brackish and hypertrophic ecosystem,the Étang de Bolmon (South of France).

A small thecate dinoflagellate was encountered during winter and spring in the phytoplankton community of a shallow, brackish and hypertrophic pond in the South of France. The abundance of material permitted its identification, using scanning electron microscopy, as Oblea rotunda Balech ex Sournia. However, morphological features showed some discrepancies with the typical characteristics of O. rotunda. Environmental hydrographic parameters in the pond were very different from marine ecosystems where O. rotunda is usually reported. In this polluted and alkaline pond, salinity was low, ranging from 1.1 to 6.2 p.s.u.; the maximum densities of O. rotunda (greater than 1?×?10⁵ cells l^???1) were observed at temperatures around 13°C, after a Cylindrotheca closterium?–?Heterocapsa rotundata bloom in early spring. These two species and other abundant taxa of the phytoplankton had seasonal patterns that could explain the presence of O. rotunda, since they could have been a food for this heterotrophic species. As this population showed most of the morphological criteria of O. rotunda, but with some variability and a different ecology, it is better considered as a variant of the marine species, rather than as a new species. This study provides additional data on the ecological and morphological features of this poorly known small peridinioid species, previously only reported from open seas and oceans.     

Purification and properties of elderberry latent virus, one of four sap-transmissible viruses obtained from American elder (Sambucus canadensis L.)

Cherry leaf roll, tomato black ring and two previously unrecorded viruses were transmitted to Chenopodium quinoa from Sambucus canadensis plants imported from the U.S.A. Of the two newly recognized viruses one, code-named elderberry virus A, has filamentous particles about 650 times 15 nm; the other, named elderberry latent virus (ELV), was transmitted to several herbaceous species but remained symptomless in elder and most other hosts. In C. quinoa sap ELV lost infectivity after dilution to 10^--⁵ to 10^-- ⁶ , 10 min at 85–90°C, and 7 days at 18°C. Infectivity of nucleic acid extracts was abolished by ribonuclease in 0.2 m sodium chloride. ELV was purified from C. quinoa leaf extracts that were clarified with chloroform, by precipitation at pH 5 and differential centrifugation. Purified preparations contained numerous isometric particles c. 30 nm in diameter and a few particles c. 17 nm in diameter. In 0.06 M phosphate buffer ELV sedimented as a major 112 S (calculated for infinite dilution) component and a 48 S minor component. ELV showed no serological relationship to twenty-seven other isometric plant viruses. Its present cryptogram is R/I: *I*:S/S:S/*.     

Sodium chloride absorption across the ileal epithelium of the lizardGallotia galloti

Summary Ion transport processes in the ileum of the lizard,Gallotia (=Lacerta) galloti was examined in vitro by measuring Na²² and Cl³⁶ fluxes across short-circuited preparations.In Ringer-bicarbonate solution there was both a net sodium flux ( ) and a net chloride flux ( ) from mucosa to serosa. The inequality between and short-circuit current (I _sc) suggests that part of the net sodium transport is the result of an electrically neutral transport mechanism or that another electrogenic mechanism opposite in sign is contributing to the short-circuit current.In the absence of sodium, the short-circuit current and net chloride flux were abolished. In the absence of chloride, the net sodium was reduced but not abolished and the short-circuit current was unchanged.From an analysis of the effects of the inhibitors furosemide, amiloride, disulfonic stilbene (DIDS) and acetazolamide, a plausible model was developed to explain the characteristics of these transports. It is proposed that the entry of sodium into the cell across the luminal membrane occurs by two pathways. Part occurs by the antiport Na⁺H⁺ and part by an electrogenic pathway. The entry of chloride is by the antiport Cl^–HCO ₃ ^– .Symbols and abbreviations DIDS 4,4 diisothiocyanatostilbene-2,2-disulfonic acid - G _t tissue conductance - I _sc short circuit current - m mucosal - PD potential difference - s serosal     

Sodium-cotransport systems in intestine and kidney of the winter flounder

Summary Brush-border membrane vesicles were isolated from the intestine and kidney of the winter flounder,Pseudopleuronectes americanus, and the transport ofd-glucose,l-alanine and sodium was examined by a rapid filtration technique.d-glucose,l-alanine, and sodium entered the same osmotically reactive space suggesting that uptake into vesicles represents transport across rather than binding to the membrane. d-glucose andl-alanine uptake by intestinal and renal brush-border membrane vesicles was stimulated by sodium as compared to potassium or choline. In the presence of a sodium chloride gradient, overshooting uptake was observed indicating a transient intravesicular accumulation ofd-glucose andl-alanine. The sodium-dependentd-glucose uptake was inhibited by phlorizin andd-galactose while the transport ofl-alanine was inhibited byl-phenylalanine. The sodium-dependent transport ofd-glucose andl-alanine was affected by the electrical potential difference across the vesicle membrane; the addition of valinomycin in the presence of an inwardly directed potassium chloride gradient inhibited sodium-dependent solute uptake, whereas replacing chloride or gluconate with more permeant anions, such as SCN^–, stimulated uptake. Similar results were obtained with intestinal and renal membranes; they document the presence of sodium/d-glucose and sodium/l-alanine cotransport systems in the brush-border membrane of intestine and kidney.Sodium uptake into brush border membrane vesicles from the flounder intestine and kidney was saturable (tracer replacement) and trans-stimulated (tracer coupling), indicating transport via facilitated diffusion systems. Additionally, sodium uptake was only slightly affected by superimposing diffusion potentials demonstrating that the majority of sodium transport was by electroneutral coupled processes. In both the intestinal and kidney brush-border membrane vesicles sodium uptake was inhibited by an inwardly directed proton gradient suggesting the presence of a sodium/proton exchange mechanism. In intestinal, but not in renal membrane preparations, sodium uptake was stimulated by chloride. Chloride stimulation was abolished after preincubation with furosemide indicating the presence of an additional coupled sodium-chloride transport in the intestinal brush-border membranes.The experiments were carried out at the Mount Desert Island Biological Laboratory, Salsbury Cove, Maine 04672, USAAddress effective February 1, 1980: Albert Einstein College of Medicine, Department of Physiology, 1300 Morris Park Avenue, Bronx, New York 10461, USA