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1.
Diurnal changes in volume and solute transport coefficients of phaseolus roots 总被引:1,自引:0,他引:1
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Fiscus EL 《Plant physiology》1986,80(3):752-759
Volume (Jv) and solute (Js) fluxes through Phaseolus root systems were observed over a 24-hour period. The volume flux was varied in a pressure chamber by altering the hydrostatic pressure in 10 steps, from 0 to 0.41 megapascals. All root systems showed strong diurnal peaks in volume flux. The five transport coefficients (σ, ω, Js*, Lp, and π*) were estimated from a nonlinear least squares algorithm. Analysis of the data revealed that all the coefficients exhibited a diurnal rhythm. When the total differential of the volume flux was considered it was possible to show that the diurnal changes in volume flux were due to a complex interaction between the diurnally shifting coefficients with the role of each highly dependent on the level of volume flux. At low volume fluxes, ω, Js*, and π* accounted for nearly all the diurnal change in volume flux. At high volume fluxes, however, the major influence shifted to Lp and π*, while ω and Js* became relatively unimportant. Thus, π* was the only coefficient of interest across the entire range of Jv and appeared to be the single most important one in determining the diurnal rhythm of Jv under conditions of a constant applied pressure. 相似文献
2.
Studies of Root Function in Zea mays: III. Xylem Sap Composition at Maximum Root Pressure Provides Evidence of Active Transport into the Xylem and a Measurement of the Reflection Coefficient of the Root 总被引:4,自引:1,他引:3
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Miller DM 《Plant physiology》1985,77(1):162-167
The cut ends of excised Zea mays roots were sealed to a pressure transducer and their root pressures recorded. These rose approximately hyperbolically to a maximum value of 4.21 ± 0.34 bar after 30 to 40 minutes. Xylem exudate could not be collected at this pressure since the flow rate was zero. Samples of exudate were collected at lower applied pressures (ΔP), however, and Δπ, the osmotic pressure difference between them and the solution bathing the root, was measured by freezing point depression. A plot of ΔP/Δπ against Jv/Δπ, where Jv is the volume flux, proved to be a straight line whose intercept, equal to σ, the reflection coefficient, was 0.853 ± 0.016. The maximum xylem concentrations of various chemical species were found by a similar extrapolative method and compared with those in the cell sap. This indicated that (a) Ca2+, Mg2+, NO32−, SO42−, and most amino acids move from the cells to the xylem down an electrochemical potential gradient; (b) relative to these ions H+, NH4+, glutamine and asparagine are actively transported into the xylem; and (c) H2PO4−, and K+ are actively retained in the symplasm. 相似文献
3.
Dilute Solution Approximation and Generalization of the Reflection Coefficient Method of Describing Volume and Solute Flows
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Donald C. Mikulecky 《Biophysical journal》1973,13(9):994-999
Kedem and Katchalsky introduced an approximation for dilute solutions which requires that the quantity (Δπ/Δπi)øi be much less than one. Zelman attempted to generalize the reflection coefficient concept to apply to solutions of multiple solutes, both penetrable and impenetrable, of concentrations sufficiently high for the approximation not to work. By simple algebraic manipulation, Zelman introduced a pair of new reflection coefficients, and a third new parameter γ which he misleadingly calls the “deviation from the dilute solution approximation.” It is shown here that the original Kedem-Katchalsky form for the flow equations can be preserved in such a way that no new coefficients need be introduced and an explicit statement of the effect of the dilute solution approximation can be made. There is an option of using a new set of conjugate driving forces for the solute flows or, alternatively, incorporating the nondilute solution correction in the coefficients in a clear way. 相似文献
4.
This paper presents a theoretical analysis of the kinetics of osmotic transport across a semipermeable membrane. There is a thermodynamic connection between the rate of flow under a hydrostatic pressure difference and the rate of flow due to a difference in solute concentration on the two sides. One might therefore attempt to calculate the osmotic transport coefficient by applying Poiseuille's equation to the flow produced by a difference in hydrostatic pressure. Such a procedure is, however, inappropriate if the pores in the membrane are too small to allow molecules to “overtake.” It then becomes necessary to perform a statistical calculation of the transport coefficient, and such a calculation is described in this paper. The resulting expression for the number of solvent molecules passing through a pore per second is J = m D1 δn1/l2 where m is the number of solvent molecules in the pore, l is the length of the pore, D1 is the self-diffusion coefficient of the solute, and δn1 the difference in solvent mole fraction on the two sides of the membrane. This equation is used for estimating the number of pores per unit area of the squid axon membrane; the result is 6 × 109 pores/cm2. 相似文献
5.
Determination of Urea Permeability in Red Cells by Minimum Method : A test of the phenomenological equations 总被引:7,自引:6,他引:1
R. I. Sha''''afi G. T. Rich D. C. Mikulecky A. K. Solomon 《The Journal of general physiology》1970,55(4):427-450
A new method has been developed for measuring the permeability coefficient, ω, of small nonelectrolytes. The method depends upon a mathematical analysis of the time course of cell volume changes in the neighborhood of the minimum volume following addition of a permeating solute to an isosmolal buffer. Coefficients determined by the minimum volume method agree with those obtained using radioactive tracers. ω for urea in human red cells was found to decrease as the volume flow, Jv, into the cell increased. Such behavior is entirely unexpected for a single uniform rate-limiting barrier on the basis of the linear phenomenological equations derived from irreversible thermodynamics. However, the present findings are consonant with a complex membrane system consisting of a tight barrier on the outer face of the human red cell membrane and a somewhat less restrictive barrier behind it closer to the inner membrane face. A theoretical analysis of such a series model has been made which makes predictions consistent with the experimental findings. 相似文献
6.
Transport Parameters in a Porous Cellulose Acetate Membrane 总被引:1,自引:1,他引:0
The transport parameters of a cellulose acetate membrane prepared from a mixture of cellulose acetate, formamide, and acetone, 25:25:50 by weight, were studied. The membrane consists of a thin, porous layer, the skin, in series with a thick, highly porous layer, the coarse support. In the skin the diffusional permeability coefficient, ω, of a number of small amides and alcohols depends critically upon the partition coefficient, Ks, the size of the molecule, and the apparent hydrogen-bonding ability, Ns, of the solute. These observations are in general agreement with our earlier conclusions on the properties of nonporous membranes. On the other hand, the corrected reflection coefficient, σ', is not a very sensitive function of either Ns or Ks taken separately. The correlation between σ' and molecular diameter is reasonably good; however, it is much improved when both Ns and Ks are taken into consideration. Isotope interaction was also studied in the present preparation and was found to provide only a small (5–8%) contribution to the diffusional permeability coefficient of ethylene glycol. The contribution of solute-water friction was found to be less than 24% of the total solute friction. 相似文献
7.
Evgeny Kobrinsky Parwiz Abrahimi Son Q. Duong Sam Thomas Jo Beth Harry Chirag Patel Qi Zong Lao Nikolai M. Soldatov 《PloS one》2009,4(5)
Background
Voltage-gated Cav1.2 calcium channels play a crucial role in Ca2+ signaling. The pore-forming α1C subunit is regulated by accessory Cavβ subunits, cytoplasmic proteins of various size encoded by four different genes (Cavβ1 - β4) and expressed in a tissue-specific manner.Methods and Results
Here we investigated the effect of three major Cavβ types, β1b, β2d and β3, on the structure of Cav1.2 in the plasma membrane of live cells. Total internal reflection fluorescence microscopy showed that the tendency of Cav1.2 to form clusters depends on the type of the Cavβ subunit present. The highest density of Cav1.2 clusters in the plasma membrane and the smallest cluster size were observed with neuronal/cardiac β1b present. Cav1.2 channels containing β3, the predominant Cavβ subunit of vascular smooth muscle cells, were organized in a significantly smaller number of larger clusters. The inter- and intramolecular distances between α1C and Cavβ in the plasma membrane of live cells were measured by three-color FRET microscopy. The results confirm that the proximity of Cav1.2 channels in the plasma membrane depends on the Cavβ type. The presence of different Cavβ subunits does not result in significant differences in the intramolecular distance between the termini of α1C, but significantly affects the distance between the termini of neighbor α1C subunits, which varies from 67 Å with β1b to 79 Å with β3.Conclusions
Thus, our results show that the structural organization of Cav1.2 channels in the plasma membrane depends on the type of Cavβ subunits present. 相似文献8.
Lingyun Shao Xinyun Zhang Yan Gao Yunya Xu Shu Zhang Shenglei Yu Xinhua Weng Hongbo Shen Zheng W. Chen Weimin Jiang Wenhong Zhang 《PloS one》2016,11(3)
Objective
Detailed studies of correlation between HIV-M.tb co-infection and hierarchy declines of CD8+/CD4+ T-cell counts and IFN-γ responses have not been done. We conducted case-control studies to address this issue.Methods
164 HIV-1-infected individuals comprised of HIV-1+ATB, HIV-1+LTB and HIV-1+TB- groups were evaluated. Immune phenotyping and complete blood count (CBC) were employed to measure CD4+ and CD8+ T-cell counts; T.SPOT.TB and intracellular cytokine staining (ICS) were utilized to detect ESAT6, CFP10 or PPD-specific IFN-γ responses.Results
There were significant differences in median CD4+ T-cell counts between HIV-1+ATB (164/μL), HIV-1+LTB (447/μL) and HIV-1+TB- (329/μL) groups. Hierarchy low CD4+ T-cell counts (<200/μL, 200-500/μL, >500/μL) were correlated significantly with active TB but not M.tb co-infection. Interestingly, hierarchy low CD8+ T-cell counts were not only associated significantly with active TB but also with M.tb co-infection (P<0.001). Immunologically, HIV-1+ATB group showed significantly lower numbers of ESAT-6-/CFP-10-specific IFN-γ+ T cells than HIV-1+LTB group. Consistently, PPD-specific IFN-γ+CD4+/CD8+ T effector cells in HIV-1+ATB group were significantly lower than those in HIV-1+LTB group (P<0.001).Conclusions
Hierarchy low CD8+ T-cell counts and effector function in HIV-1-infected individuals are correlated with both M.tb co-infection and active TB. Hierarchy low CD4+ T-cell counts and Th1 effector function in HIV-1+ individuals are associated with increased frequencies of active TB, but not M.tb co-infection. 相似文献9.
Effect of single mutations in the OGG1 gene found in human tumors on the substrate specificity of the Ogg1 protein 总被引:4,自引:2,他引:2
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We have investigated the effect of single amino acid substitutions of conserved arginines on the catalytic activities of the human Ogg1 protein (α-hOgg1-Ser326) (wild-type α-hOgg1). Mutant forms of hOgg1 with mutations Arg46→Gln (α-hOgg1-Gln46) and Arg154→His (α-hOgg1-His154) have previously been identified in human tumors. The mutant proteins α-hOgg1-Gln46 and α-hOgg1-His154 were expressed in Escherichia coli and purified to homogeneity. The substrate specificities of these proteins and wild-type α-hOgg1 were investigated using γ-irradiated DNA and the technique of gas chromatography/isotope-dilution mass spectrometry. All three enzymes excised 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) and 8-hydroxyguanine (8-OH-Gua) from γ-irradiated DNA containing a multiplicity of base lesions. Michaelis–Menten kinetics of excision were measured. Significant differences between excision kinetics of these three enzymes were observed. Excision of FapyGua and 8-OH-Gua by wild-type α-hOgg1 was greater than that by α-hOgg1-Gln46 and α-hOgg1-His154. The latter mutant protein was less active than the former. The diminished activity of the mutant proteins was more pronounced for 8-OH-Gua than for FapyGua. Cleavage assays were also performed using 32P-labeled 34mer oligonucleotide duplexes containing a single 8-OH-Gua paired to each of the four DNA bases. The results obtained with the oligonucleotide containing the 8-OH-Gua/Cyt pair were in good agreement with those observed with γ-irradiated DNA. Wild-type α-hOgg1 and its mutants repaired the three mismatches less efficiently than the 8-OH-Gua/Cyt pair. The substitution of Arg154, in addition to diminishing the activity on 8-OH-Gua, relaxes the selectivity found in the wild-type α-hOgg1 for the base opposite 8-OH-Gua. Taken together the results show that the mutant forms α-hOgg1-Gln46 and α-hOgg1-His154 found in human tumors are defective in their catalytic capacities. 相似文献
10.
11.
A Physical Interpretation of the Phenomenological Coefficients of Membrane Permeability 总被引:19,自引:11,他引:19
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A "translation" of the phenomenological permeability coefficients into friction and distribution coefficients amenable to physical interpretation is presented. Expressions are obtained for the solute permeability coefficient ω and the reflection coefficient σ for both non-electrolytic and electrolytic permeants. An analysis of the coefficients is given for loose membranes as well as for dense natural membranes where transport may go through capillaries or by solution in the lipoid parts of the membrane. Water diffusion and filtration and the relation between these and capillary pore radius of the membrane are discussed. For the permeation of ions through the charged membranes equations are developed for the case of zero electrical current in the membrane. The correlation of σ with ω and Lp for electrolytes resembles that for non-electrolytes. In this case ω and σ depend markedly on ion concentration and on the charge density of the membrane. The reflection coefficient may assume negative values indicating anomalous osmosis. An analysis of the phenomena of anomalous osmosis was carried out for the model of Teorell and Meyer and Sievers and the results agree with the experimental data of Loeb and of Grim and Sollner. A set of equations and reference curves are presented for the evaluation of ω and σ in the transport of polyvalent ions through charged membranes. 相似文献
12.
13.
Studies of Root Function in Zea mays: IV. Effects of Applied Pressure on the Hydraulic Conductivity and Volume Flow through the Excised Root 总被引:1,自引:0,他引:1
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Miller DM 《Plant physiology》1985,77(1):168-174
The volume flux, Jv, and the osmotic driving force, σπ, across excised root systems of Zea mays were measued as a function of P, the hydrostatic pressure difference applied across the root, using the pressure jump method previously described (Miller DM 1980 Can J Bot 58: 351-360). Jv varied from 5.3% to 142% of its value in intact transpiring plants as a result of the application of pressure differences from −2.4 to 2.4 bar. The calculated hydraulic conductivity was 5.9 × 10−4 cubic centimeters per second per bar per gram root and was independent of pressure. A model of root function similar to those appearing in the literature failed to provide quantitative accord with the data. A proposed model, which includes the effect of volume flux on the distribution of solutes in the symplasm, predicts accurately Jv π, and the xylem solute concentration as a function of P. 相似文献
14.
Sedimentation-Diffusion Equilibrium of Monomer-Dimer Mixtures, Studied in the Analytical Ultracentrifuge
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Jean E. Morel 《Biophysical journal》1986,49(2):579-580
By generalizing the fundamental differential equation valid for a single ideal solute, it is usual to define, for a monomer-dimer nonideal mixture, an apparent molecular weight Mw,app = (2RT/[1 - ρV]ω2) (d lnc/dr2); RT has the usual meaning; ρ is the density of the solvent; V is the partial specific volume of the solute, assumed to be the same for the monomer and the dimer; w is the angular velocity of the rotor; c is the solute concentration at the radial position r in the cell. It is shown here that the above equation can be integrated in the case of a monomer-dimer nonideal mixture and that, after integration, we obtain the following relation between c and r: ([1 + 4Kc]1/2 - 1)/([1 + 4Kc0]1/2 - 1]) exp (BMm[c - c0]) = exp ([σm/2] [r2 - r02]); σm = Mm(1 - ρV)ω2/RT (Mm = molecular weight of the monomer); K is the monomer-dimer equilibrium constant; B is the second virial coefficient, assumed to be the same for the monomer and the dimer. As soon as Mm is known, the above equation permits the calculation of K and B, from the experimental curve c(r). Moreover, the reversibility of the monomer-dimer equilibrium can be tested from this equation: it is necessary and sufficient that the values of K corresponding to different loading concentrations in the cell are identical. 相似文献
15.
One of the major flow phenomena associated with low Reynolds number flow is the formation of separation bubbles on an airfoil’s surface. NACA4415 airfoil is commonly used in wind turbines and UAV applications. The stall characteristics are gradual compared to thin airfoils. The primary criterion set for this work is the capture of laminar separation bubble. Flow is simulated for a Reynolds number of 120,000. The numerical analysis carried out shows the advantages and disadvantages of a few turbulence models. The turbulence models tested were: one equation Spallart Allmars (S-A), two equation SST K-ω, three equation Intermittency (γ) SST, k-kl-ω and finally, the four equation transition γ-Reθ SST. However, the variation in flow physics differs between these turbulence models. Procedure to establish the accuracy of the simulation, in accord with previous experimental results, has been discussed in detail. 相似文献
16.
Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes 总被引:2,自引:2,他引:0
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Michel BE 《Plant physiology》1983,73(1):66-70
Published and additional data for polyethylene glycol 8000 (PEG), formerly PEG 6000, solution water potentials (Ψ) are compared. Actual bars Ψ over the concentration range of 0 to 0.8 gram PEG per gram H2O and temperature (T) range of 5 to 40°C are best predicted (probably within ± 5%) by this equation: Ψ = 1.29[PEG]2T − 140[PEG]2 − 4.0[PEG]. Although transformable through division by [PEG] to virial equation form, results indicate that the coefficients are not virial. Mannitol (MAN) interacts with PEG to produce Ψ significantly lower than additive. Vapor pressure osmometer (VPO) data for MAN-PEG synergism compared favorably with those from thermocouple hygrometry; and VPO data showing the interactions between PEG and four salts are presented. The synergism of MAN-PEG and of NaCl-PEG are related linearly to the concentration of solute added with PEG. 相似文献
17.
Francesco De Cobelli Giulio Pezzetti Sergio Margari Antonio Esposito Francesco Giganti Giulia Agostini Alessandro Del Maschio 《PloS one》2015,10(4)
Introduction
Abdominal pain in PNH has never been investigated by in-vivo imaging studies. With MRI, we aimed to assess mesenteric vessels flow and small bowel wall perfusion to investigate the ischemic origin of abdominal pain.Materials and Methods
Six PNH patients with (AP) and six without (NOP) abdominal pain underwent MRI. In a blinded fashion, mean flow (MF, quantity of blood moving through a vessel within a second, in mL·s-1) and stroke volume (SV, volume of blood pumped out at each heart contraction, in mL) of Superior Mesenteric Vein (SMV) and Artery (SMA), areas under the curve at 60 (AUC60) and 90 seconds (AUC90) and Ktrans were assessed by two operators.Results
Mean total perfusion and flow parameters were lower in AP than in NOP group. AUC60: 84.81 ± 11.75 vs. 131.73 ± 18.89 (P < 0.001); AUC90: 102.33 ± 14.16 vs. 152.58 ± 22.70 (P < 0.001); Ktrans: 0.0346 min-1 ± 0.0019 vs. 0.0521 ± 0.0015 (P = 0.093 duodenum, 0.009 jejunum/ileum). SMV: MF 4.67 ml/s ± 0.85 vs. 8.32 ± 2.14 (P = 0.002); SV 3.85 ml ± 0.76 vs. 6.55 ± 1.57 (P = 0.02). SMA: MF 6.95 ± 2.61 vs. 11.2 ± 2.32 (P = 0.07); SV 6.52 ± 2.19 vs. 8.78 ± 1.63 (P = 0.07). We found a significant correlation between MF and SV of SMV and AUC60 (MF:ρ = 0.88, P < 0.001; SV: ρ = 0.644, P = 0.024), AUC90 (MF: ρ = 0.874, P < 0.001; SV:ρ = 0.774, P = 0.003) and Ktrans (MF:ρ = 0.734, P = 0.007; SV:ρ = 0.581, P = 0.047).Conclusions
Perfusion and flow MRI findings suggest that the impairment of small bowel blood supply is significantly associated with abdominal pain in PNH. 相似文献18.
Marina Koutsioumpa Christos Polytarchou José Courty Yue Zhang Nelly Kieffer Constantinos Mikelis Spyros S. Skandalis Ulf Hellman Dimitrios Iliopoulos Evangelia Papadimitriou 《The Journal of biological chemistry》2013,288(1):343-354
The multifunctional protein nucleolin (NCL) is overexpressed on the surface of activated endothelial and tumor cells and mediates the stimulatory actions of several angiogenic growth factors, such as pleiotrophin (PTN). Because αvβ3 integrin is also required for PTN-induced cell migration, the aim of the present work was to study the interplay between NCL and αvβ3 by using biochemical, immunofluorescence, and proximity ligation assays in cells with genetically altered expression of the studied molecules. Interestingly, cell surface NCL localization was detected only in cells expressing αvβ3 and depended on the phosphorylation of β3 at Tyr773 through receptor protein-tyrosine phosphatase β/ζ (RPTPβ/ζ) and c-Src activation. Downstream of αvβ3, PI3K activity mediated this phenomenon and cell surface NCL was found to interact with both αvβ3 and RPTPβ/ζ. Positive correlation of cell surface NCL and αvβ3 expression was also observed in human glioblastoma tissue arrays, and inhibition of cell migration by cell surface NCL antagonists was observed only in cells expressing αvβ3. Collectively, these data suggest that both expression and β3 integrin phosphorylation at Tyr773 determine the cell surface localization of NCL downstream of the RPTPβ/ζ/c-Src signaling cascade and can be used as a biomarker for the use of cell surface NCL antagonists as anticancer agents. 相似文献
19.
Paul R. Dohrmann Raul Correa Ryan L. Frisch Susan M. Rosenberg Charles S. McHenry 《Nucleic acids research》2016,44(3):1285-1297
There is widespread agreement that the clamp loader of the Escherichia coli replicase has the composition DnaX3δδ’χψ. Two DnaX proteins exist in E. coli, full length τ and a truncated γ that is created by ribosomal frameshifting. τ binds DNA polymerase III tightly; γ does not. There is a controversy as to whether or not DNA polymerase III holoenzyme (Pol III HE) contains γ. A three-τ form of Pol III HE would contain three Pol IIIs. Proponents of the three-τ hypothesis have claimed that γ found in Pol III HE might be a proteolysis product of τ. To resolve this controversy, we constructed a strain that expressed only τ from a mutated chromosomal dnaX. γ containing a C-terminal biotinylation tag (γ-Ctag) was provided in trans at physiological levels from a plasmid. A 2000-fold purification of Pol III* (all Pol III HE subunits except β) from this strain contained one molecule of γ-Ctag per Pol III* assembly, indicating that the dominant form of Pol III* in cells is Pol III2τ2 γδδ’χψ. Revealing a role for γ in cells, mutants that express only τ display sensitivity to ultraviolet light and reduction in DNA Pol IV-dependent mutagenesis associated with double-strand-break repair, and impaired maintenance of an F’ episome. 相似文献
20.
Diffusive and convective transport coefficients of Phaseolus vulgaris L. cv. Ouray root systems for abscisic acid for (ABA) were measured. The convective coefficient (reflection coefficient or osmotic efficiency factor) σ was determined to be 0.96 for ABA while the diffusive coefficient, ω, was found to be 1.44 × 10−11 mole per square centimeter per second per bar. Steady-state concentrations of ABA in the root system exudates were not achieved until at least three hours after the applications suggesting either a slow saturation of binding sites or equilibration with tissues surrounding the xylem. 相似文献