Cryopreservation of Atlantic salmon Salmo salar sperm: effects on sperm physiology

The objective of this study was to determine the effect of freezing on the function in Atlantic salmon Salmo salar spermatozoa. The semen was frozen in Cortland's medium + 1.3M dimethyl sulphoxide + 0.3M glucose + 2% bovine serum albumin (final concentration) in a ratio of 1:3 (semen:cryoprotectant) as the treatment (T) and fresh semen as the control (F). Straws of 0·5 ml of sperm suspension were frozen in 4 cm of N₂L. They were thawed in a thermoregulated bath (40° C). After thawing, the percentage of spermatozoa with fragmented DNA [transferase dUTP (deoxyuridine triphosphate) nick‐end labelling (TUNEL)], plasma membrane integrity (SYBR‐14/PI) and mitochondrial membrane potential (ΔΨMMit, JC‐1) were evaluated by flow cytometry and motility was evaluated by optical microscope under stroboscopic light. The fertilization rates of the control and treatment semen were tested at a sperm density of 1·5 × 10⁷ spermatozoa oocyte^?1, by observation of the first cleavages after 16 h incubation at 10° C. In the cryopreserved semen (T), the mean ± s.d . DNA fragmentation was 4·8 ± 2·5%; plasma membrane integrity 75·2 ± 6·3%; mitochondrial membrane potential 51·7 ± 3·6%; motility 58·5 ± 5·3%; curved line velocity (V_CL) 61·2 ± 17·4 µm s^?1; average‐path velocity (V_AP) 50·1 ± 17·3 µm s^?1; straight‐line velocity (V_SL) 59·1 ± 18·4 µm s^?1; fertilization rate 81·6 ± 1·9%. There were significant differences in the plasma membrane integrity, mitochondrial membrane potential, motility, fertilization rate, V_CL, V_AP and V_SL compared with the controls (P < 0·05). Also the mitochondrial membrane potential correlated with motility, fertilization rate, V_CL and V_SL (r = 0·75; r = 0·59; r = 0·77 and r = 0·79, respectively; P < 0·05); and the fertilization rate correlated with V_CL and V_SL (r = 0·59 and r = 0·55, respectively).     

β‐Cell Function and Insulin Sensitivity in Adolescents From an OGTT

Given the increase in the incidence of insulin resistance, obesity, and type 2 diabetes in children and adolescents, it would be of paramount importance to assess quantitative indices of insulin secretion and action during a physiological perturbation, such as a meal or an oral glucose‐tolerance test (OGTT). A minimal model method is proposed to measure quantitative indices of insulin secretion and action in adolescents from an oral test. A 7 h, 21‐sample OGTT was performed in 11 adolescents. The C‐peptide minimal model was identified on C‐peptide and glucose data to quantify indices of β‐cell function: static φ_s and dynamic φ_d responsivity to glucose from which total responsivity φ was also measured. The glucose minimal model was identified on glucose and insulin data to estimate insulin sensitivity, S_I, which was compared to a reference measure, S_I^ref, provided by a tracer method. Disposition indices, which adjust insulin secretion for insulin action, were then calculated. Indices of β‐cell function were φ_s = 51.35 ± 8.89 × 10^?9min^?1, φ_d = 1,392 ± 258 × 10^?9, and φ = 82.09 ± 17.70 × 10^?9min^?1. Insulin sensitivity was S_I = 14.19 ± 2.73 × 10^?4, not significantly different from S_I^ref = 14.96 ± 3.04 × 10^?4 dl/kg·min per µU/ml, and well correlated: r = 0.98, P < 0.0001, thus indicating that S_I can be accurately measured from an oral test. Disposition indices were DI_s = 1,040 ± 201 × 10^?14 dl/kg/min² per pmol/l, DI_d = 33,178 ± 10,720 × 10^?14 dl/kg/min per pmol/l, DI = 1,844 ± 522 × 10^?14 dl/kg/min² per pmol/l. Virtually the same minimal model assessment was obtained with a reduced 3 h, 9‐sample protocol. OGTT interpreted with C‐peptide and glucose minimal model has the potential to provide novel insight regarding the regulation of glucose metabolism in adolescents, and to evaluate the effect of obesity and interventions such as diet and exercise.     

Four‐Compartment Cellular Level Body Composition Model: Comparison of Two Approaches**

Objective: The aim of this study was to develop and compare two DXA‐based four‐compartment [body weight = body cell mass (BCM) + extracellular fluid (ECF) + extracellular solids (ECS) + fat] cellular level models. Research Methods and Procedures: Total body potassium (TBK) model: BCM from TBK by whole‐body counting—ECF_TBK = LST ? [BCM_TBK + 0.73 × osseous mineral (Mo)]. Bromide model: ECF from sodium bromide dilution—BCM_BROMIDE = LST ? (ECF_BROMIDE + 0.73 × Mo); Mo and LST measurements came from DXA. The two approaches were evaluated in 99 healthy men and 118 women. Results: BCM estimates were highly correlated (r = 0.97, p < 0.001), as were ECF estimates (r = 0.87, p < 0.001); a small statistically significant mean difference was present (mean ± SD; BCM_TBK model, 30.4 ± 8.9 kg; BCM_BROMIDE, 31.4 ± 9.3 kg; Δ = 1.0 ± 2.8 kg; p < 0.001; ECF_TBK, 18.5 ± 4.2 kg; ECF_BROMIDE, 17.5 ± 3.6 kg; Δ = 1.0 ± 2.8 kg; p < 0.001). A high correlation (r = 0.97, p < 0.001) and good agreement (38.9 ± 9.5 vs. 38.9 ± 9.5 kg; Δ = 0.0 ± 2.4 kg; p = 0.39) were present between TBW, derived as the sum of intracellular water from TBK and ECW from bromide, and measured TBW by ²H₂O dilution. Discussion: Two developed four‐compartment cellular level DXA models, one of which is appropriate for use in most clinical and research settings, provide comparable results and are applicable for BCM and ECF estimation of subject groups with hydration disturbances.     

Power consumption and maximum energy dissipation in a milliliter‐scale bioreactor

Mean power consumption and maximum local energy dissipation were measured as function of operating conditions of a milliliter‐scale stirred tank bioreactor (V = 12 mL) with a gas‐inducing impeller. A standard laboratory‐scale stirred tank bioreactor (V = 1,200 mL) with Rushton turbines was used as reference. The measured power characteristics (Newton number as function of Reynolds number) were the same on both scales. The changeover between laminar and turbulent flow regime was observed at a Reynolds number of 3,000 with the gas‐inducing stirrer on a milliliter‐scale. The Newton number (power number) in the turbulent flow regime was 3.3 on a milliliter‐scale, which is close to values reported for six‐blade Rushton turbines of standard bioreactors. Maximum local energy dissipation (ε_max) was measured using a clay/polymer flocculation system. The maximum local energy dissipation in the milliliter‐scale stirred tank bioreactor was reduced compared with the laboratory‐scale stirred tank at the same mean power input per unit mass (ε_ø), yielding ε_max/ε_ø ≈ 10 compared with ε_max/ε_ø ≈ 16. Hence, the milliliter‐scale stirred tank reactor distributes power more uniformly in the reaction medium. These results are in good agreement with literature data, where a decreasing ε_max/ε_ø with increasing ratio of impeller diameter to reactor diameter is found (d/D = 0.7 compared with d/D = 0.4). Based on these data, impeller speeds can now be easily adjusted to achieve the same maximum local energy dissipation at different scales. This enables a more reliable and robust scale‐up of bioprocesses from milliliter‐scale to liter‐scale reactors. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Dimeric chlorite dismutase from the nitrogen‐fixing cyanobacterium Cyanothece sp. PCC7425

It is demonstrated that cyanobacteria (both azotrophic and non‐azotrophic) contain heme b oxidoreductases that can convert chlorite to chloride and molecular oxygen (incorrectly denominated chlorite ‘dismutase’, Cld). Beside the water‐splitting manganese complex of photosystem II, this metalloenzyme is the second known enzyme that catalyses the formation of a covalent oxygen–oxygen bond. All cyanobacterial Clds have a truncated N‐terminus and are dimeric (i.e. clade 2) proteins. As model protein, Cld from Cyanothece sp. PCC7425 (CCld) was recombinantly produced in Escherichia coli and shown to efficiently degrade chlorite with an activity optimum at pH 5.0 [k_cat 1144 ± 23.8 s^?1, K_M 162 ± 10.0 μM, catalytic efficiency (7.1 ± 0.6) × 10⁶ M^?1 s^?1]. The resting ferric high‐spin axially symmetric heme enzyme has a standard reduction potential of the Fe(III)/Fe(II) couple of ?126 ± 1.9 mV at pH 7.0. Cyanide mediates the formation of a low‐spin complex with k_on = (1.6 ± 0.1) × 10⁵ M^?1 s^?1 and k_off = 1.4 ± 2.9 s^?1 (K_D ～ 8.6 μM). Both, thermal and chemical unfolding follows a non‐two‐state unfolding pathway with the first transition being related to the release of the prosthetic group. The obtained data are discussed with respect to known structure–function relationships of Clds. We ask for the physiological substrate and putative function of these O₂‐producing proteins in (nitrogen‐fixing) cyanobacteria.     

Soil CO2 efflux measurements in a mixed forest: impact of chamber disturbances,spatial variability and seasonal evolution

A closed‐dynamic‐chamber system (CDCS) was used to measure the spatial and seasonal variability of the soil CO₂ efflux (F_s) in beech and in Douglas fir patches of the Vielsalm forest (Belgium). First the difference between natural and measured soil CO₂ efflux induced by the presence of the CDCS was studied. The impact on the measurements of the pressure difference between the outside (natural condition) and the inside of the chamber was found to be small (0.4%). The influence of wind disturbance in the closed chamber was tested by comparison with an open‐chamber system characterized by a different wind distribution. A very good correlation between the two systems was found (r² = 0.99) but the open system yielded slightly lower fluxes than the closed one (slope = 0.88 ± 0.05). A measurement procedure has been developed to minimize the effect of the other sources of perturbation. The spatial and seasonal evolution of the soil CO₂ efflux was obtained by performing regular measurements on 29 spots in the beech patch over a period of 12 months and on 24 spots in the Douglas fir patch over 8 months. For each spot, the experimental relationship between Fs and soil temperature was compared with the fitted line for an Arrhenius relationship with a soil temperature‐dependent activation energy. Soil temperature explains 73% of the seasonal variation for all the data. The spatial average of the soil CO₂ efflux at 10 °C (Fs₁₀) in the beech patch is 2.57 ± 0.41 μmol m^?2 s^?1, approximately twice the average in the Douglas fir patch recorded at 1.42 ± 0.22 μmol m^?2 s^?1. The litter fall analysis seems to indicate that soil organic matter quality and quantity may be one the reasons for this difference. Finally the annual soil CO₂ efflux was calculated for the beech and Douglas fir patches (870 ± 140 and 438 ± 68 gC m^?2 y^?1, respectively). The beech value would represent 92 ± 15% of the annual ecosystem respiration estimated from the eddy covariance measurements.     

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii. Part II: Definition of model‐based protocols and experimental validation

Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus‐shaped PBR in sulfur‐deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232–245). This allowed a strictly autotrophic production, whereas the sulfur‐deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m⁻² s⁻¹). Maximum hydrogen productivities were 1.0 ± 0.2 mL H₂/h/L (or 25 ± 5 mL H₂/m² h) and 3.1 mL ± 0.4 H₂/h L (or 77.5 ± 10 mL H₂/m² h), at 110 and 500 µmol photons m⁻² s⁻¹, respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H₂/h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed. Biotechnol. Bioeng. 2011;108: 2288–2299. © 2011 Wiley Periodicals, Inc.     

Physicochemical studies on xylinan (acetan). III. Hydrodynamic characterization by analytical ultracentrifugation and dynamic light scattering

A laboratory-made sample of the polysaccharide xylinan (acetan) has been further characterized with respect to (i) purity, (ii) molar mass and polydispersity, and (iii) gross conformation by a combination of hydrodynamic measurements (sedimentation velocity and equilibrium analytical ultracentrifugation, viscometry, and dynamic light scattering) in aqueous NaCl (I = 0.10 mol·L⁻¹). Sedimentation velocity diagrams recorded using Schlieren optics revealed highly pure material sedimenting as a single boundary [s^o_20.w = 9.5 ± 0.7) S; k_s = (273 ± 112) mL/g]. The hypersharp nature of these boundaries is symptomatic of a polydisperse and highly nonideal (in the thermodynamic sense) system. Low speed sedimentation equilibrium in the analytical ultracentrifuge using Rayleigh interference optics and two different types of extrapolation procedure (involving point and whole-cell molar masses) gave a weight average molar mass M_w of (2.5 ± 0.5) × 10⁻⁶ g·mol⁻¹ and also a second virial coefficient, B = (2.8 ± 0.7) × 10⁻⁴ mL·mol·g⁻², both values in good agreement with those from light scattering-based procedures (Part II of this series). A dynamic Zimm plot from dynamic light scattering measurements gave a z-average translational diffusion coefficient D^o_20.w = (3.02 ± 0.05) × 10⁻⁸ cm²·s⁻¹ and the concentration-dependence parameter k_D = (370 ± 15) mL/g. Combination of s^o_20.w with D^o_20.w via the Svedberg equation gave another estimate for M_w of ≅ 2.4 × 10⁶ g/mol, again in good agreement. Both the Wales-van Holde ratio (k_s/[η]) ≅ 0.4 (with [η] = (760 ± 77) mL/g) and the ρ-parameter (ratio of the radius of gyration from static light scattering to the hydrodynamic radius from dynamic light scattering) as ρ > 2.0 all indicate an extended conformation for the macromolecules in solution. These findings, plus Rinde-type simulations of the sedimentation equilibrium data are all consistent with the interpretation in terms of a unimodal wormlike coil model performed earlier. © 1996 John Wiley & Sons, Inc.     

Structure of native proteoglycan aggregates from chick limb-bud chondrocytes

Laser light-scattering has been used to investigate the size of native proteoglycan aggregates (PGA-aA1) from day-8 chick limb-bud chondrocyte cultures isolated under associative extraction and purification conditions in 0.4M guanidinium chloride (GdnHCl) solution. Dynamic light-scattering measurements yielded a hydrodynamic radius, R_s, of 244 ± 10 nm for PGA-aA1 in 0.4M GdnHCl, and a weight-average molecular weight (M _w) of 150 ± 50 × 10⁶ was obtained from a Zimm plot. Disaggregation in 4.0M GdnHCl aqueous solution yielded proteoglycan subunits (PGS) with R_s = 39 ± 2 nm, M _w = 1.6 ± 0.3 × 10⁶, which reassembled in 0.4M GdnHCl to form “reconstituted native” aggregates (PGA-raA1) with R_s = 121 ± 6 nm, M _w = 17 ± 3 × 10⁶. A second specimen of PGA-aA1 had R_s = 192 ± 10 nm, M _w = 100 ± 10 × 10⁶. The latter value was estimated from an empirical relationship between M _w and R_s. After dissociation, this specimen reassembled to form PGA-raA1 with R_s = 85 ± 5 nm, M _w = 12 ± 1 × 10⁶. These data are compared with those for a specimen of reconstituted aggregate (PGA-A1) that had been extracted under dissociative conditions and then reaggregated by dialysis to 0.4M GdnHCl aqueous solution, for which R_s = 138 ± 9 nm, M _w = 45 ± 8 × 10⁶. From these values, we have calculated the weight-average number of subunits per aggregate N_w: 111 for PGA-aA1 and 12 for raA1 (70 and 7 for the second PGA-aA1 and PGA-raA1 specimen, respectively) as compared to 32 for PGA-A1. The numbers of subunits per aggregate were also determined from electron micrographs of spread specimens. The latter results show the same trends as those obtained by light scattering, but lead in each case to lower numbers of subunits per aggregate. These data demonstrate conclusively that PGA samples exhibit a higher degree of aggregation in solution than visualized in typical electron microscopy (EM) preparations, probably due to disaggregation during EM specimen preparation. Since N_w determined both by light scattering (LS) and by EM are larger for native versus reconstituted aggregate samples, our data point to a more compact aggregation of subunits along the hyaluronic acid (HA) chains in the former.     

Molybdenum isotope fractionation by cyanobacterial assimilation during nitrate utilization and N₂ fixation

We measured the δ⁹⁸Mo of cells and media from molybdenum (Mo) assimilation experiments with the freshwater cyanobacterium Anabaena variabilis, grown with nitrate as a nitrogen (N) source or fixing atmospheric N₂. This organism uses a Mo‐based nitrate reductase during nitrate utilization and a Mo‐based dinitrogenase during N₂ fixation under culture conditions here. We also demonstrate that it has a high‐affinity Mo uptake system (ModABC) similar to other cyanobacteria, including marine N₂‐fixing strains. Anabaena variabilis preferentially assimilated light isotopes of Mo in all experiments, resulting in fractionations of ?0.2‰ to ?1.0‰ ± 0.2‰ between cells and media (ε_{cells–media}), extending the range of biological Mo fractionations previously reported. The fractionations were internally consistent within experiments, but varied with the N source utilized and for different growth phases sampled. During growth on nitrate, A. variabilis consistently produced fractionations of ?0.3 ± 0.1‰ (mean ± standard deviation between experiments). When fixing N₂, A. variabilis produced fractionations of ?0.9 ± 0.1‰ during exponential growth, and ?0.5 ± 0.1‰ during stationary phase. This pattern is inconsistent with a simple kinetic isotope effect associated with Mo transport, because Mo is likely transported through the ModABC uptake system under all conditions studied. We present a reaction network model for Mo isotope fractionation that demonstrates how Mo transport and storage, coordination changes during enzymatic incorporation, and the distribution of Mo inside the cell could all contribute to the total biological fractionations. Additionally, we discuss the potential importance of biologically incorporated Mo to organic matter‐bound Mo in marine sediments.     

Modeling to discern nitrogen fertilization impacts on carbon sequestration in a Pacific Northwest Douglas‐fir forest in the first‐postfertilization year

This study investigated how nitrogen (N) fertilization with 200 kg N ha^?1 of urea affected ecosystem carbon (C) sequestration in the first‐postfertilization year in a Pacific Northwest Douglas‐fir (Pseudotsuga menziesii) stand on the basis of multiyear eddy‐covariance (EC) and soil‐chamber measurements before and after fertilization in combination with ecosystem modeling. The approach uses a data‐model fusion technique which encompasses both model parameter optimization and data assimilation and minimizes the effects of interannual climatic perturbations and focuses on the biotic and abiotic factors controlling seasonal C fluxes using a prefertilization 9‐year‐long time series of EC data (1998–2006). A process‐based ecosystem model was optimized using the half‐hourly data measured during 1998–2005, and the optimized model was validated using measurements made in 2006 and further applied to predict C fluxes for 2007 assuming the stand was not fertilized. The N fertilization effects on C sequestration were then obtained as differences between modeled (unfertilized stand) and EC or soil‐chamber measured (fertilized stand) C component fluxes. Results indicate that annual net ecosystem productivity in the first‐post‐N fertilization year increased by～83%, from 302 ± 19 to 552 ± 36 g m^?2 yr^?1, which resulted primarily from an increase in annual gross primary productivity of～8%, from 1938 ± 22 to 2095 ± 29 g m^?2 yr^?1 concurrent with a decrease in annual ecosystem respiration (R_e) of～5.7%, from 1636 ± 17 to 1543 ± 31 g m^?2 yr^?1. Moreover, with respect to respiration, model results showed that the fertilizer‐induced reduction in R_e (～93 g m^?2 yr^?1) principally resulted from the decrease in soil respiration R_s (～62 g m^?2 yr^?1).     

Seasonal variability of the parameters of the Ball–Berry model of stomatal conductance in maize (Zea mays L.) and sunflower (Helianthus annuus L.) under well‐watered and water‐stressed conditions

The Ball–Berry (BB) model of stomatal conductance (g_s) is frequently coupled with a model of assimilation to estimate water and carbon exchanges in plant canopies. The empirical slope (m) and ‘residual’ g_s (g₀) parameters of the BB model influence transpiration estimates, but the time‐intensive nature of measurement limits species‐specific data on seasonal and stress responses. We measured m and g₀ seasonally and under different water availability for maize and sunflower. The statistical method used to estimate parameters impacted values nominally when inter‐plant variability was low, but had substantial impact with larger inter‐plant variability. Values for maize (m = 4.53 ± 0.65; g₀ = 0.017 ± 0.016 mol m^?2 s^?1) were 40% higher than other published values. In maize, we found no seasonal changes in m or g₀, supporting the use of constant seasonal values, but water stress reduced both parameters. In sunflower, inter‐plant variability of m and g₀ was large (m = 8.84 ± 3.77; g₀ = 0.354 ± 0.226 mol m^?2 s^?1), presenting a challenge to clear interpretation of seasonal and water stress responses – m values were stable seasonally, even as g₀ values trended downward, and m values trended downward with water stress while g₀ values declined substantially.     

Biochemical and biophysical characterisation of haloalkane dehalogenases DmrA and DmrB in Mycobacterium strain JS60 and their role in growth on haloalkanes

Haloalkane dehalogenases (HLDs) catalyse the hydrolysis of haloalkanes to alcohols, offering a biological solution for toxic haloalkane industrial wastes. Hundreds of putative HLD genes have been identified in bacterial genomes, but relatively few enzymes have been characterised. We identified two novel HLDs in the genome of Mycobacterium rhodesiae strain JS60, an isolate from an organochlorine‐contaminated site: DmrA and DmrB. Both recombinant enzymes were active against C2–C6 haloalkanes, with a preference for brominated linear substrates. However, DmrA had higher activity against a wider range of substrates. The kinetic parameters of DmrA with 4‐bromobutyronitrile as a substrate were K_m = 1.9 ± 0.2 mM, k_cat = 3.1 ± 0.2 s^?1. DmrB showed the highest activity against 1‐bromohexane. DmrA is monomeric, whereas DmrB is tetrameric. We determined the crystal structure of selenomethionyl DmrA to 1.7 Å resolution. A spacious active site and alternate conformations of a methionine side‐chain in the slot access tunnel may contribute to the broad substrate activity of DmrA. We show that M. rhodesiae JS60 can utilise 1‐iodopropane, 1‐iodobutane and 1‐bromobutane as sole carbon and energy sources. This ability appears to be conferred predominantly through DmrA, which shows significantly higher levels of upregulation in response to haloalkanes than DmrB.     

Hierarchical Classification I: Single-Linkage Method

This is the first part of a survey of hierarchical clustering algorithms using joining methods: the Single-Linkage algorithm. Complete-Linkage and general algorithms defined by d(A_i, B) = = α,d(A_i, A_r)±α_sd(A_i, A_s)±βd(A_r, A_s) will be discussed in two subsequent papers.     

The function of water channels in Chara: The temperature dependence of water and solute flows provides evidence for composite membrane transport and for a slippage of small organic solutes across water channels

Using the cell pressure probe, the effects of temperature on hydraulic conductivity (Lp; osmotic water permeability), solute permeability (permeability coefficient, P_s), and reflection coefficients (σ_s) were measured on internodes of Chara corallina, Klein ex Willd., em R.D.W.. For the first time, complete sets of transport coefficients were obtained in the range between 10 and 35 °C which provided evidence about pathways of water and solutes as they move across the plasma membrane (water channel and bilayer arrays). Test solutes used to check for the selectivity of water channels were monohydric alcohols of different molecular size and shape (ethanol, n-propanol, iso-propanol, and tert-butanol) and heavy water (HDO). Within the limits of accuracy, Q₁₀ values for Lp and for the diffusive water permeability (P_d) were identical (Q₁₀ for Lp = 1.29 ± 0.17 (± SD; n = 15 cells) and Q₁₀ for P_d = 1.25 ± 0.16 (n = 5 cells)). The Q₁₀ values were equivalent to activation energies of E_a = 16.8 ± 6.4 and 16.6 ± 10.0 kJ · mol⁻¹, respectively, which is similar to that of self-diffusion or of viscous flow of water. The Q₁₀ values and activation energies for P_s of the alcohols were significantly larger (ethanol: Q₁₀ = 1.68 ± 0.16, E_a = 37.1 ± 5.9 kJ · mol⁻¹; n-propanol: Q₁₀ =  1.75 ± 0.40, E_a = 43.1 ± 15.3 kJ · mol⁻¹; iso-propanol: Q₁₀ = 2.12 ± 0.42, E_a =  52.2 ± 14.6 kJ · mol⁻¹; tert-butanol: Q₁₀ = 2.13 ± 0.56, E_a = 51.6 ± 17.1 kJ · mol⁻¹; ±SD; n = 5 to 6 cells). Effects of temperature on reflection coefficients were most pronounced. With increasing temperature, σ_s values of the alcohols decreased and those of HDO increased. The data indicate that water and solutes use different pathways when crossing the membrane. Ordinary and isotopic water use water channels and the other test solutes use the bilayer array (composite transport model of membrane). Changes in σ_s values with temperature were found to be a sensitive measure for the open/closed state of water channels. The decrease of σ_s with temperature was theoretically predicted from the temperature dependence of P_s and Lp. Differences between predicted and measured values of σ_s allowed estimation of the bypass flow (slippage) of solutes through water channels which did not completely exclude test solutes. The permeability of channels depended on the structure and size of test solutes. It is concluded that water channels are much less selective than is usually thought. Since water channels represent single-file or no-pass pores, solutes drag along considerable amounts of water as they diffuse across channels. This results in low overall values of σ_s. The σ_s of HDO was extremely low. Its response to temperature was opposite to that for the σ_s of the alcohols. This suggested a stronger effect of temperature on the hydraulic (osmotic) than on the diffusive water flow across individual water channels, i.e. a differential sensitivity of different mechanisms to temperature. Received: 10 October 1996 / Accepted: 2 December 1996     

Solvent‐dependent conformation of amylose tris(phenylcarbamate) as deduced from scattering and viscosity data

The z‐average mean‐square radius of gyration 〈S²〉_z, the particle scattering function P(k), the second virial coefficient, and the intrinsic viscosity [η] have been determined for amylose tris(phenylcarbamate) (ATPC) in methyl acetate (MEA) at 25°C, in ethyl acetate (EA) at 33°C, and in 4‐methyl‐2‐pentanone (MIBK) at 25°C by light and small‐angle X‐ray scattering and viscometry as functions of the weight‐average molecular weight in a range from 2 × 10⁴ to 3 × 10⁶. The first two solvents attain the theta state, whereas the last one is a good solvent for the amylose derivative. Analysis of the 〈S²〉_z, P(k), and [η] data based on the wormlike chain yields h (the contour length or helix pitch per repeating unit) = 0.37 ± 0.02 and λ^?1 (the Kuhn segment length) = 15 ± 2 nm in MEA, h = 0.39 ± 0.02 and λ^?1 = 17 ± 2 nm in EA, and h = 0.42 ± 0.02 nm and λ^?1 = 24 ± 2 nm in MIBK. These h values, comparable with the helix pitches (0.37–0.40 nm) per residue of amylose triesters in the crystalline state, are somewhat larger than the previously determined h of 0.33 ± 0.02 nm for ATPC in 1,4‐dioxane and 2‐ethoxyethanol, in which intramolecular hydrogen bonds are formed between the C?O and NH groups of the neighbor repeating units. The slightly extended helices of ATPC in the ketone and ester solvents are most likely due to the replacement of those hydrogen bonds by intermolecular hydrogen bonds between the NH groups of the polymer and the carbonyl groups of the solvent. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 729–736, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

New fin-line devices for radiofrequency exposure of small biological samples in vitro allowing whole-cell patch clamp recordings

The development and analysis of three waveguides for the exposure of small biological in vitro samples to mobile communication signals at 900 MHz (GSM, Global System for Mobile Communications), 1.8 GHz (GSM), and 2 GHz (UMTS, Universal Mobile Telecommunications System) is presented. The waveguides were based on a fin‐line concept and the chamber containing the samples bathed in extracellular solution was placed onto two fins with a slot in between, where the exposure field concentrates. Measures were taken to allow for patch clamp recordings during radiofrequency (RF) exposure. The necessary power for the achievement of the maximum desired specific absorption rate (SAR) of 20 W/kg (average over the mass of the solution) was approximately P_in = 50 mW, P_in = 19 mW, and P_in = 18 mW for the 900 MHz, 1800 MHz, and 2 GHz devices, respectively. At 20 W/kg, a slight RF‐induced temperature elevation in the solution of no more than 0.3 °C was detected, while no thermal offsets due to the electromagnetic exposure could be detected at the lower SAR settings (2, 0.2, and 0.02 W/kg). A deviation of 10% from the intended solution volume yielded a calculated SAR deviation of 8% from the desired value. A maximum ±10% variation in the local SAR could occur when the position of the patch clamp electrode was altered within the area where the cells to be investigated were located. Bioelectromagnetics 32:102–112, 2011. © 2010 Wiley‐Liss, Inc.     

Plant response to climate change along the forest‐tundra ecotone in northeastern Siberia

Russia's boreal (taiga) biome will likely contract sharply and shift northward in response to 21st century climatic change, yet few studies have examined plant response to climatic variability along the northern margin. We quantified climate dynamics, trends in plant growth, and growth–climate relationships across the tundra shrublands and Cajander larch (Larix cajanderi Mayr.) woodlands of the Kolyma river basin (657 000 km²) in northeastern Siberia using satellite‐derived normalized difference vegetation indices (NDVI), tree ring‐width measurements, and climate data. Mean summer temperatures (T_s) increased 1.0 °C from 1938 to 2009, though there was no trend (P > 0.05) in growing year precipitation or climate moisture index (CMI_gy). Mean summer NDVI (NDVI_s) increased significantly from 1982 to 2010 across 20% of the watershed, primarily in cold, shrub‐dominated areas. NDVI_s positively correlated (P < 0.05) with T_s across 56% of the watershed (r = 0.52 ± 0.09, mean ± SD), principally in cold areas, and with CMI_gy across 9% of the watershed (r = 0.45 ± 0.06), largely in warm areas. Larch ring‐width measurements from nine sites revealed that year‐to‐year (i.e., high‐frequency) variation in growth positively correlated (P < 0.05) with June temperature (r = 0.40) and prior summer CMI (r = 0.40) from 1938 to 2007. An unexplained multi‐decadal (i.e., low‐frequency) decline in annual basal area increment (BAI) occurred following the mid‐20th century, but over the NDVI record there was no trend in mean BAI (P > 0.05), which significantly correlated with NDVI_s (r = 0.44, P < 0.05, 1982–2007). Both satellite and tree‐ring analyses indicated that plant growth was constrained by both low temperatures and limited moisture availability and, furthermore, that warming enhanced growth. Impacts of future climatic change on forests near treeline in Arctic Russia will likely be influenced by shifts in both temperature and moisture, which implies that projections of future forest distribution and productivity in this area should take into account the interactions of energy and moisture limitations.     

Empirical standard mass equation for Salmo marmoratus

Total length (L_T) (range 24–1000 mm; mean ±s.e . = 170·21 ± 0·36 mm) and mass (W) (range 0·10–9590 g; mean ±s.e . = 76·03 ± 0·87 g) of 36 460 specimens of marble trout Salmo marmoratus were used to compute a standard mass (W_s) equation for this species by means of the empirical percentile (EmP) method. The EmP W_s equation calculated was: log₁₀W_s = ?5·208 + 3·202 log₁₀L_T? 0·046 (log₁₀L_T)² (L_T range 90–570 mm) and it is valid throughout the species' area of distribution across Europe.