Ionic Permeability of Thin Lipid Membranes : Effects of n-alkyl alcohols,polyvalent cations,and a secondary amine

Ultrathin (black) lipid membranes were made from sheep red cell lipids dissolved in n-decane. The presence of aliphatic alcohols in the aqueous solutions bathing these membranes produced reversible changes in the ionic permeability, but not the osomotic permeability. Heptanol (8 mM), for example, caused the membrane resistance (R_m) to decrease from >10⁸ to about 10⁵ ohm-cm² and caused a marked increase in the permeability to cations, especially potassium. In terms of ionic transference numbers, deduced from measurements of the membrane potential at zero current, T _cat/T _Cl increased from about 6 to 21 and T _K/T _Na increased from about 3 to 21. The addition of long-chain (C₈ndash;C₁₀) alcohols to the lipid solutions from which membranes were made produced similar effects on the ionic permeability. A plot of log R_m vs. log alcohol concentration was linear over the range of maximum change in R_m, and the slope was -3 to -5 for C₂ through C₇ alcohols, suggesting that a complex of several alcohol molecules is responsible for the increase in ionic permeability. Membrane permselectivity changed from cationic to anionic when thorium or ferric iron (10^-4 M) was present in the aqueous phase or when a secondary amine (Amberlite LA-2) was added to the lipid solutions from which membranes were made. When membranes containing the secondary amine were exposed to heptanol, R_m became very low (10³–10⁴ ohm-cm²) and the membranes became perfectly anion-selective, developing chloride diffusion potentials up to 150 mv.     

Leaf litter diversity alters microbial activity,microbial abundances,and nutrient cycling in a subtropical forest ecosystem

Human activities affect both tree species composition and diversity in forested ecosystems. This in turn alters the species diversity of plant litter and litter quality, which may have cascading effects on soil microbial communities and their functions for decomposition and nutrient cycling. We tested microbial responses to litter species diversity in a leaf litter decomposition experiment including monocultures, 2-, and 4-species mixtures in the subtropical climate zone of southeastern China. Soil microbial community composition was assessed by lipid analysis, and microbial functions were measured using extracellular enzyme activity and gross rates of nitrogen mineralization. We observed a positive relationship between litter species diversity and abundances of mycorrhizal fungi and actinomycetes. Alternatively, enzyme activities involved in carbon and phosphorus acquisition, and enzyme indices of relative carbon limitation, were higher only in the 4-species mixtures. This suggests that the minimum basal substrate level for enzyme production was reached, or that limitation was higher, at the highest diversity level only. Responses to litter diversity also changed over time, where phosphatase responses to litter diversity were strongest early in decomposition and the indices of carbon limitation relative to other nutrients showed stronger responses later in decomposition. Enzyme activities were related to lipid biomarker data and the mass of litter remaining at the third time point, but relationships between enzyme activity and the mass of litter remaining were not consistent across other time points. We conclude that litter species richness will likely only reduce microbial functions at key intervals of diversity loss while microbial growth is more sensitive to incremental diversity loss, with no clear relationships between them or to ecosystem functions. The observed litter diversity effects on soil microbial biomass and enzyme activity indicate interactions of aboveground and belowground communities, and together with environmental conditions they are important for maintaining ecosystem functions.     

Tree Species Traits but Not Diversity Mitigate Stem Breakage in a Subtropical Forest following a Rare and Extreme Ice Storm

Future climates are likely to include extreme events, which in turn have great impacts on ecological systems. In this study, we investigated possible effects that could mitigate stem breakage caused by a rare and extreme ice storm in a Chinese subtropical forest across a gradient of forest diversity. We used Bayesian modeling to correct stem breakage for tree size and variance components analysis to quantify the influence of taxon, leaf and wood functional traits, and stand level properties on the probability of stem breakage. We show that the taxon explained four times more variance in individual stem breakage than did stand level properties; trees with higher specific leaf area (SLA) were less susceptible to breakage. However, a large part of the variation at the taxon scale remained unexplained, implying that unmeasured or undefined traits could be used to predict damage caused by ice storms. When aggregated at the plot level, functional diversity and wood density increased after the ice storm. We suggest that for the adaption of forest management to climate change, much can still be learned from looking at functional traits at the taxon level.     

Biogeographic differences in plant–soil biota relationships contribute to the exotic range expansion of Verbascum thapsus

1. Exotic plant species can evolve adaptations to environmental conditions in the exotic range. Furthermore, soil biota can foster exotic spread in the absence of negative soil pathogen–plant interactions or because of increased positive soil biota–plant feedbacks in the exotic range. Little is known, however, about the evolutionary dimension of plant–soil biota interactions when comparing native and introduced ranges.
2. To assess the role of soil microbes for rapid evolution in plant invasion, we subjected Verbascum thapsus, a species native to Europe, to a reciprocal transplant experiment with soil and seed material originating from Germany (native) and New Zealand (exotic). Soil samples were treated with biocides to distinguish between effects of soil fungi and bacteria. Seedlings from each of five native and exotic populations were transplanted into soil biota communities originating from all populations and subjected to treatments of soil biota reduction: application of (a) fungicide, (b) biocide, (c) a combination of the two, and (d) control.
3. For most of the investigated traits, native populations showed higher performance than exotic populations; there was no effect of soil biota origin. However, plants developed longer leaves and larger rosettes when treated with their respective home soil communities, indicating that native and exotic plant populations differed in their interaction with soil biota origin. The absence of fungi and bacteria resulted in a higher specific root length, suggesting that V. thapsus may compensate the absence of mutualistic microbes by increasing its root–soil surface contact.
4. Synthesis. Introduced plants can evolve adaptations to soil biota in their new distribution range. This demonstrates the importance of biogeographic differences in plant–soil biota relationships and suggests that future studies addressing evolutionary divergence should account for differential effects of soil biota from the home and exotic range on native and exotic populations of successful plant invaders.

     

The GA genotype of the −1154 G/A (rs1570360) vascular endothelial growth factor (VEGF) is protective against hypertension-related chronic kidney disease incidence

Vascular endothelial growth factor (VEGF) is a highly specific mitogen with angiogenic and vascular permeability activities for endothelial cells. VEGF participates in maintaining the renal vasculature integrity. There is no doubt that hypertension accelerates progression to renal dysfunction, resulting in chronic kidney disease (CKD). The purpose of our study was to examine the VEGF −1154 G/A (rs1570360) polymorphism among hypertensive patients with CKD. Additionally markers of endothelial damage have been related to the advancement of CKD. There were 96 consecutively admitted hypertensive patients referred to our Institution by their general practitioner. The patients were treated with an anti-hypertensive polytherapy. Ninety-nine healthy volunteers were enrolled as the control group. Our study revealed that both healthy and hypertensive groups frequencies of the genotypes varied significantly (p = 0.030, χ ² test). The GA genotype frequency was significantly lower among patients in comparison with healthy. The presence of GA genotype was connected with a decreased risk of hypertension disease (OR = 0.48, p = 0.01). The VEGF −1154 GA carriers have been associated with the lowest values of Endostatin (p = 0.020), Angiogenin (p = 0.040) as well as vWf (p = 0.005). The GA genotype has been characterized by the highest values of eGFR (p = 0.024) and the lowest values of creatinine (p = 0.028) and BUN (p = 0.012). It is evident that the GA genotype of VEGF polymorphism localized at −1154 position is a genetic protective factor for development arterial hypertension and is associated with less progressed CKD.

     

Cloning and mapping of a testis-specific gene with sequence similarity to a sperm-coating glycoprotein gene

A testis-specific gene Tpx-1, located between Pgk-2 and Mep-1 on mouse chromosome 17, was isolated from a cosmid clone, and its cDNA sequences were determined. The predicted coding sequence of Tpx-1 isolated from BALB/c mice showed 64.2% nucleotide and 55.1% amino acid sequence similarity with that of a rat sperm-coating glycoprotein gene, the protein product of which is secreted by the epididymis. To examine the evolutionary relationship between Tpx-1 and a sperm-coating glycoprotein gene, the cDNA sequence of TPX1, the human counterpart of Tpx-1, was determined. The comparison of the predicted coding sequences of Tpx-1 and TPX1 showed 77.8% nucleotide and 70% amino acid sequence similarity. Since Tpx-1 (from mouse) is more similar to TPX1 (from man) than it is to a rat sperm-coating glycoprotein gene, we conclude that Tpx-1 (TPX1) and a sperm-coating glycoprotein gene are closely related, but distinct, genes belonging to the same gene family. The predicted Tpx-1 protein of a t mutant mouse CRO437 differs from that of BALB/c mice by one amino acid insertion in the putative signal peptide. TPX1 was mapped to 6p21-qter by Southern blot analysis of interspecies somatic hybrid cell lines.     

Cadmium and thallous ion permeabilities through lipid bilayer membranes

Cadmium (Cd2+) and thallous ion (Tl+) permeabilities were measured in planar (Mueller-Rudin) lipid bilayer membranes made from diphytanoylphosphatidylcholine in decane. Permeabilities of the electroneutral Cl- complexes, measured with tracers (109Cd and 204Tl), were about 10(-8) cm X s-1 for CdCl2 and 10(-6) cm X s-1 for TlCl. Electrical conductance measurements showed that permeabilities to Cd2+ and Tl+ were approx. 10(-11) cm X s-1, similar to the Na+ permeability. The low permeabilities to both Cd2+ and CdCl2 are consistent with biological studies which suggest that Cd transport and toxicity are protein mediated and correlated with Cd2+, not CdCl2, concentration. However, the low bilayer permeability to Tl+ raises questions about recent reports that Tl+ is a lipid permeable cation in biological membranes and liposomes. An alternative explanation for the lipid permeable behavior of Tl+ is presented, based on the diffusion of TlCl and other complexes of Tl+ with inorganic and organic anions.     

The permeability of thin lipid membranes to bromide and bromine

Thin lipid (optically black) membranes were made from sheep red cell lipids dissolved in n-decane. The flux of Br across these membranes was measured by the use of tracer ⁸²Br. The unidirectional flux of Br (in 50–100 mM NaBr) was 1–3 x 10^-12 mole/cm²sec. This flux is more than 1000 times the flux predicted from the membrane electrical resistance (>10⁸ ohm-cm²) and the transference number for Br^- (0.2–0.3), which was estimated from measurements of the zero current potential difference. The Br flux was not affected by changes in the potential difference imposed across the membrane (±60 mv) or by the ionic strength of the bathing solutions. However, the addition of a reducing agent, sodium thiosulfate (10^-3 M), to the NaBr solution bathing the membrane caused a 90% reduction in the Br flux. The inhibiting effect of S₂O₃ ⁼ suggests that the Br flux is due chiefly to traces of Br₂ in NaBr solutions. As expected, the addition of Br₂ to the NaBr solutions greatly stimulated the Br flux. However, at constant Br₂ concentration, the Br flux was also stimulated by increasing the Br^- concentration, in spite of the fact that the membrane was virtually impermeable to Br^-. Finally, the Br flux appeared to saturate at high Br₂ concentrations, and the saturation value was roughly proportional to the Br^- concentration. These results can be explained by a model which assumes that Br crosses the membrane only as Br₂ but that rapid equilibration of Br between Br₂ and Br^- occurs in the unstirred layers of aqueous solution bathing the two sides of the membrane. A consequence of the model is that Br^- "facilitates" the diffusion of Br across the unstirred layers.     

Ion Fluxes and Short-Circuit Current in Internally Perfused Cells of Valonia ventricosa

Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (I _sc) was 97 pEq/cm² sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm² sec) and large net influxes of K (80 pEq/cm² sec) and Cl (50 pEq/cm² sec). Unidirectional K influx was proportional to I _sc, but more than one-half of the I _sc remained unaccounted for. Both the I _sc and PD were partly light-dependent, declining rapidly during the first 1–2 min of darkness. Ouabain (5 x 10^-4 M) had little effect on the influx of Na or K and had no effect on I _inf or PD. Fluid was absorbed at a rate of about 93 pliter/cm² sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared.     

Proton/hydroxide conductance through phospholipid bilayer membranes: effects of phytanic acid

Mechanisms of proton/hydroxide conductance (GH/OH) were investigated in planar (Mueller-Rudin) bilayer membranes made from decane solutions of phospholipids or phospholipids plus phytanic acid (a 20-carbon, branched chain fatty acid). At neutral pH, membranes made from diphytanoylphosphatidylcholine or bacterial phosphatidylethanolamine had GH/OH values in the range of (2-5) X 10(-9) S X cm-2, corresponding to H+/OH- 'net' permeabilities of about (0.4-1.0) X 10(-5) cm X s-1. GH/OH was inhibited by serum albumin, phloretin, glycerol and low pH, but was increased by chlorodecane and voltage greater than 80 mV. Water permeability and GH/OH were not correlated, suggesting that water and H+/OH- cross the membrane by separate pathways. Addition of phytanic acid to the phospholipids caused an increase in GH/OH which was proportional to the first power of the phytanic acid concentration. In membranes containing phytanic acid, GH/OH was inhibited by albumin, phloretin, glycerol and low pH, but was increased by chlorodecane and voltages greater than 80 mV. The results suggest that phytanic acid acts as a simple (A- type) proton carrier. The qualitative similarities between the behavior of GH/OH in unmodified and phytanic-acid containing membranes suggest that phospholipids may contain weakly acidic contaminants which cause most of GH/OH at pH greater than 4. However, there is also a significant background (pH independent) GH/OH which may be due to hydrogen-bonded water chains. The ability of phytanic acid to act as a proton carrier may help to explain the toxicity of phytanic acid in Refsum's disease, a metabolic disorder in which phytanic acid accumulates to high levels in plasma, cells and tissues.