How does salt retention raise blood pressure?

A critical question in hypertension research is: How is long-term blood pressure controlled? Excessive NaCl ingestion or NaCl retention by the kidneys and the consequent tendency toward plasma volume expansion lead to hypertension. Nevertheless, the precise mechanisms linking salt to high blood pressure are unresolved. The discovery of endogenous ouabain, an adrenocortical hormone, provided an important clue. Ouabain, a selective Na+ pump inhibitor, has cardiotonic and vasotonic effects. Plasma endogenous ouabain levels are significantly elevated in approximately 40% of patients with essential hypertension and in animals with several forms of salt-dependent hypertension. Also, prolonged ouabain administration induces hypertension in rodents. Mice with mutant Na+ pumps or Na/Ca exchangers (NCX) and studies with a ouabain antagonist and an NCX blocker are revealing the missing molecular mechanisms. These data demonstrate that alpha2 Na+ pumps and NCX1 participate in long-term regulation of vascular tone and blood pressure. Pharmacological agents or mutations in the alpha2 Na+ pump that interfere with the action of ouabain on the pump, and reduced NCX1 expression or agents that block NCX all impede the development of salt-dependent or ouabain-induced hypertension. Conversely, nanomolar ouabain, reduced alpha2 Na+ pump expression, and smooth muscle-specific overexpression of NCX1 all induce hypertension. Furthermore, ouabain and reduced alpha2 Na+ pump expression increase myogenic tone in isolated mesenteric small arteries in vitro, thereby tying these effects directly to the elevation of blood pressure. Thus, endogenous ouabain, and vascular alpha2 Na+ pumps and NCX1, are critical links between salt and hypertension. New pharmacological agents that act on these molecular links have potential in the clinical management of hypertension.     

Managed re-alignment; a salt marsh dilemma?

Managed re-alignment of sea defences is seen as the way to strengthen these by rationalising the line between land and sea and creating a buffer of inter-tidal habitat in front of them. This buffer is most commonly salt marsh which absorbs wave energy thus protecting the defences. The global area of salt marsh is in decline due to a range of issues and managed re-alignment is a way of creating or recreating this important habitat. This review examines managed re-alignment schemes in the light of salt marsh loss, rising sea levels and a changing climate. The ecosystem services and benefits provided by salt marsh can be assessed and given a monetary value. Managed re-alignment can be an important tool for salt marsh creation and coastal zone management. The number and size of schemes in the UK has increased in recent years but the area of recreated salt marsh is still insufficient to replace that lost by erosion and other processes. Background data from a proposed site, and adjacent areas likely to be affected, need to be collected prior to embarking on a scheme that may prove successful. Stakeholder interests cannot be neglected and there will also be a need for long-term monitoring. Re-created salt marshes may form an effective sea defence buffer but they remain significantly different from adjacent natural marshes for many years both in their vegetation and functional equivalence.     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

Do salt bridges stabilize proteins? A continuum electrostatic analysis

The electrostatic contribution to the free energy of folding was calculated for 21 salt bridges in 9 protein X-ray crystal structures using a continuum electrostatic approach with the DELPHI computer-program package. The majority (17) were found to be electrostatically destabilizing; the average free energy change, which is analogous to mutation of salt bridging side chains to hydrophobic isosteres, was calculated to be 3.5 kcal/mol. This is fundamentally different from stability measurements using pKa shifts, which effectively measure the strength of a salt bridge relative to 1 or more charged hydrogen bonds. The calculated effect was due to a large, unfavorable desolvation contribution that was not fully compensated by favorable interactions within the salt bridge and between salt-bridge partners and other polar and charged groups in the folded protein. Some of the salt bridges were studied in further detail to determine the effect of the choice of values for atomic radii, internal protein dielectric constant, and ionic strength used in the calculations. Increased ionic strength resulted in little or no change in calculated stability for 3 of 4 salt bridges over a range of 0.1-0.9 M. The results suggest that mutation of salt bridges, particularly those that are buried, to "hydrophobic bridges" (that pack at least as well as wild type) can result in proteins with increased stability. Due to the large penalty for burying uncompensated ionizable groups, salt bridges could help to limit the number of low free energy conformations of a molecule or complex and thus play a role in determining specificity (i.e., the uniqueness of a protein fold or protein-ligand binding geometry).     

Kinetic and equilibrium studies of bile salt–liposome interactions

Abstract

Research has suggested that exposure to sub-micellar concentrations of bile salts (BS) increases the permeability of lipid bilayers in a time-dependent manner. In this study, incubation of soy phosphatidylcholine small unilamellar vesicles (liposomes) with sub-micellar concentrations of cholate (C), deoxycholate (DC), 12-monoketocholate (MKC) or taurocholate (TC) in pH 7.2 buffer increased membrane fluidity and negative zeta potential in the order of increasing BS liposome-pH 7.2 buffer distribution coefficients (MKC?<?C?≈?TC?<?DC). In liposomes labeled with the dithionite-sensitive fluorescent lipid N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanolamine (NBD-PE) in both leaflets and equilibrated with sub-micellar concentrations of BS, fluorescence decline during continuous exposure to dithionite was biphasic involving a rapid initial phase followed by a slower second phase. Membrane permeability to dithionite as measured by the rate of the second phase increased in the order control?<?MKC?<?TC?～?C?<?DC. In liposomes labeled with NBD-PE in the inner leaflet only and incubated with the same concentrations of C, DC and MKC, membrane permeability to dithionite initially increased very rapidly in the order MKC?<?C?<?DC before impermeability to dithionite was restored after which fluorescence decline was consistent with NBD-PE flip-flop. For liposomes incubated with TC, membrane permeability to dithionite was only slightly increased and the decline in fluorescence was mainly the result of NBD-PE flip-flop. These results provide evidence that BS interact with lipid bilayers in a time-dependent manner that is different for conjugated and unconjugated BS. MKC appears to cause least disturbance to liposomal membranes but, when the actual MKC concentration in liposomes is taken into account, MKC is actually the most disruptive.     

Hydrocarbon degradation potential of salt marsh plant–microorganisms associations

Estuaries are often considered sinks for contaminants and the cleanup of salt marshes, sensitive ecosystems with a major ecological role, should be carried out by means of least intrusive approaches, such as bioremediation. This study was designed to evaluate the influence of plant–microorganisms associations on petroleum hydrocarbons fate in salt marshes of a temperate estuary (Lima River, NW Portugal). Sediments un-colonized and colonized (rhizosediments) by different plants (Juncus maritimus, Phragmites australis, Triglochin striata and Spartina patens) were sampled in four sites of the lower and middle estuary for hydrocarbon degrading microorganisms (HD), total cell counts (TCC) and total petroleum hydrocarbons (TPHs) assessment. In general, TPHs, HD and TCC were significantly higher (P < 0.05) in rhizosediments than in un-colonized sediments. Also recorded were differences on the abundance of hydrocarbon degraders among the rhizosediment of the different plants collected at the same site (J. maritimus < P. australis < T. striata), with statistically significant differences (P < 0.05) between J. maritimus and T. striata. Moreover, strong positive correlations—0.81 and 0.84 (P < 0.05), between biotic (HD) and abiotic (organic matter content) parameters and TPHs concentrations were also found. Our data clearly suggest that salt marsh plants can influence the microbial community, by fostering the development of hydrocarbon-degrading microbial populations in its rhizosphere, an effect observed for all plants. This effect, combined with the plant capability to retain hydrocarbons around the roots, points out that salt marsh plant–microorganisms associations may actively contribute to hydrocarbon removal and degradation in estuarine environments.     

Extraction of cartilage protein–polysaccharides with inorganic salt solutions

1. Bovine nasal cartilage was extracted with inorganic salt solutions of various ionic strengths. The efficiency of extraction of protein-polysaccharide from the tissue was determined for each extraction. The results confirm and enlarge earlier observations (Sajdera & Hascall, 1969). 2. The chloride salts of lanthanide metals extract high yields of protein-polysaccharide from the tissue at much lower concentrations than was achieved with univalent and bivalent salts. 3. The lanthanum salt of extracted protein-polysaccharide precipitates when the concentration of LaCl(3) is decreased. Precipitation is complete in the presence of 0.05m-LaCl(3). This finding is relevant to the interpretation of earlier observations on the effect of LaCl(3) on elastic recovery of articular cartilage after compression (Sokoloff, 1963). 4. A linear relationship was found between the concentration at which a particular salt is maximally effective in solubilizing protein-polysaccharide from the tissue and the enthalpy of hydration of the cation of the salt. On the basis of this relationship a hypothesis is proposed to explain the characteristic protein-polysaccharide-extraction profiles exhibited by inorganic salt solutions.     

What do we know about salt stress in bryophytes?

Bryophytes are among the first plants that faced the terrestrial way of life. They settled almost all terrestrial habitats, but no extant seawater representatives are known. It is not widely documented how bryophytes cope with salt stress, but there are species inhabiting salty environments. Here, we present the current state of knowledge on salt stress biology in bryophytes.     

Alleviation of salt stress by low dose γ-irradiation in rice

The effects of salt stress on the growth, photosynthesis, and antioxidative ability of the rice (Oryza sativa L.) plants raising from -irradiated seeds were investigated using two cultivars, Ilpumbyeo and Sanghaehyanghyella. The 50 and 100 mM NaCl solutions caused a remarkable decrease of the early germination rate and seedling growth. However, the salt stress-induced inhibition of the growth was significantly alleviated in the -irradiated plants. The chlorophyll contents and the effective quantum yield of photosystem 2 ( _{PS 2}) were lower in the NaCl-treated plants than in the control ones, while the non-photochemical quenching was higher in the former ones. Activities of the antioxidant enzymes such as superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased with increasing NaCl concentrations, and the irradiated groups had even higher SOD and APX activities than the non-irradiated ones. These alleviation effects were observed similarly in both the cultivars tested.     

Phospholipase Dδ assists to cortical microtubule recovery after salt stress

The dynamic microtubule cytoskeleton plays fundamental roles in the growth and development of plants including regulation of their responses to environmental stress. Plants exposed to hyper-osmotic stress commonly acclimate, acquiring tolerance to variable stress levels. The underlying cellular mechanisms are largely unknown. Here, we show, for the first time, by in vivo imaging approach that linear patterns of phospholipase Dδ match the localization of microtubules in various biological systems, validating previously predicted connection between phospholipase Dδ and microtubules. Both the microtubule and linear phospholipase Dδ structures were disintegrated in a few minutes after treatment with oryzalin or salt. Moreover, by using immunofluorescence confocal microscopy of the cells in the root elongation zone of Arabidopsis, we have shown that the cortical microtubules rapidly depolymerized within 30 min of treatment with 150 or 200 mM NaCl. Within 5 h of treatment, the density of microtubule arrays was partially restored. A T-DNA insertional mutant lacking phospholipase Dδ showed poor recovery of microtubule arrays following salt exposition. The restoration of microtubules was significantly retarded as well as the rate of root growth, but roots of overexpressor GFP-PLDδ prepared in our lab, have grown slightly better compared to wild-type plants. Our results indicate that phospholipase Dδ is involved in salt stress tolerance, possibly by direct anchoring and stabilization of de novo emerging microtubules to the plasma membrane, providing novel insight into common molecular mechanism during various stress events.     

Effect of salt stress on photosystem Ⅱ heterogeneity in wheat leaves

In order to study the effects of salt stress on photosystem Ⅱ (PSⅡ) heterogeneity, signal from the fluorometer was digitized via a microcomputer interface to record PSⅡ fluorescence induction kinetics. Changes of parameters (Fm, Fp1 and F0) from the fast phase of fluorescence induction curve showed that the percentage of QB-nonreducing PSⅡ reaction centers dropped at first, and then rose with the increase of stress intensity and time. This indicated that the electron transfer from QA to QB is one of the sites where the photochemical and photophysical processes of PSⅡ are damaged by the salt stress.     

Role of AT₁ receptor-mediated salt retention in angiotensin II-dependent hypertension

Activation of type 1 angiotensin II (AT(1)) receptors in the kidney promotes blood pressure elevation and target organ damage, but whether renal AT(1) receptors influence the level of hypertension by stimulating sodium retention or by raising systemic vascular resistance has not been established. In the current studies, we used a kidney cross-transplantation strategy to determine whether increased sodium reabsorption by AT(1) receptors in the kidney mediates the chronic hypertensive response to angiotensin II. We found this to be true. In addition, we also identified a second, nontrivial component of blood pressure elevation induced by activation of renal AT(1) receptors that is sodium-independent. As the kidney has the capacity to limit the transmission of elevated systemic blood pressure into the renal microcirculation, prior studies struggled to clearly discriminate the relative contributions of blood pressure elevation vs. activation of AT(1) receptors to hypertensive kidney injury. In our model, we found that rapid surges in blood pressure, which may overcome the kidney's capacity to prevent perturbations in renal hemodynamics, correlate closely with kidney damage in hypertension. Moreover, maximal kidney injury in hypertension may require activation of a pool of nonrenal, systemic AT(1) receptors. These studies provide insight into precise mechanisms through which AT(1) receptor blockade influences the progression of hypertensive kidney disease.     

Construction of two regulatory networks related to salt stress and lignocellulosic synthesis under salt stress based on a Populus davidiana × P. bolleana transcriptome analysis

Plant Molecular Biology - Construction of ML-hGRN for the salt pathway in Populus davidiana?×?P. bolleana. Construction of ML-hGRN for the lignocellulosic pathway in Populus...     

Temporal dynamics of three culturable γ-Proteobacteria taxa in salt marsh sediments

Temporal dynamics of three marine -Proteobacteria taxa withculturable members were followed in sediment communities in southeastern USsaltmarshes using a whole-genome hybridization approach. Labeled DNA from threebacterial isolates was used to probe sediment community DNA from two saltmarshes on Sapelo Island, GA at multiple time points over a three-year period.The relative abundance of the three isolates (and their close relatives)accounted for up to 28% of the total sediment community DNA. Hybridizationsignals for the taxon represented by isolate SIGA28M (with a 16S rRNA sequencesimilarity of 97% to Vibrio proteolyticus) showedsignificant temporal variation in both marshes, varying from 1% to 28% over thethree-year period. The taxa represented by isolates SIGA172a and SIGA198 (16SrRNA sequence similarities of 90% and 92% to Shewanellafrigidimarina and Vibrio nigripulchritudo,respectively) accounted for less than 6% of the sediment community at any timepoint. The variation in relative abundance of these three groups did not appearto follow clear seasonal trends, and could not be readily correlated withenvironmental variables.     

Shoot δ15N correlates with genotype and salt stress in barley

Given a uniform N source, the ¹⁵N of barley shoots provided a genotypic range within treatments and a separation between control and salt-stress treatments as great as did ¹³C^*. Plant ¹⁵N has been represented in the literature as a bioassay of external source ¹⁵N and used to infer soil N sources, thus precluding consideration of the plant as a major cause in determining its own 8¹⁵N. We believe this to be the first report of plant ¹⁵N as a genetic trait. No mechanistic model is needed for use of ¹⁵N as a trait in controlled studies; however, a qualitative model is suggested for further testing.Symbol ¹⁵N (or ¹³C) the difference between: (1) the ratio of heavy to light isotopes of the element in a sample and (2) that of its reference standard     

Insensitivity to road salt: an advantage for the American bullfrog?

The health of freshwater ecosystems is negatively affected by a multitude of pollutants. In northern latitudes, road deicing agents enter nearby ponds and waterways elevating chloride concentrations in winter and spring. Few studies have examined how amphibians respond to road salt contamination and no study has focused on the response of an invasive amphibian. We examined the effects of NaCl, the most commonly used deicing agent, on the embryos and tadpoles of the American bullfrog, Lithobates catesbeianus, a species that is invasive in many regions around the world. In the first experiment, we exposed L. catesbeianus embryos to ecologically relevant levels of chloride for 60 days. The second experiment examined the indirect consequences of chloride contamination by exposing L. catesbeianus tadpoles to dragonfly larvae. Lithobates catesbeianus did not experience reduced survival, growth, or ability to evade predation in elevated chloride concentrations compared to controls. The lack of a response by L. catesbeianus suggests that its population growth will not be negatively impacted by road salt contamination. This result may be good news for L. catesbeianus, but raises concern for sympatric amphibians that have to contend with negative impacts of both chloride contamination and non-native L. catesbeianus.