Relative Permeability Coefficients Research Articles

Biophysical characterization of a large conductance anion channel in hypodermal membranes of the gastrointestinal nematode, Ascaris suum

Patch-clamp recordings from muscle- and cuticle-facing hypodermal membranes of the gastrointestinal nematode Ascaris suum reveal a high-conductance, voltage- sensitive Ca 2+ -dependent Cl − channel. The hypodermal channel has a conductance of 195 pS in symmetrical 160 mM NaCl. The open probability of the channel is highly voltage-sensitive, and channel activity is not observed when Ca 2+ is reduced to <100 μM. The channel is permeable to organic anions that are major end-products of carbohydrate metabolism in A. suum, including acetate, butyrate and 2-methylvalerate. The conductances and relative permeabilities of these organic anions are inversely related to size, with 2-methylvalerate being only approximately 3% as permeable as Cl −. The diameter of the channel pore was 12.3±0.2 Å, calculated from the relative permeability coefficients of Cl − and the organic anions. Results of this study are consistent with the hypothesis that the large conductance anion channel in A. suum hypodermal membranes provides a low energy pathway for organic anion excretion from the hypodermal compartment, followed by diffusion across the aqueous channels of the cuticle matrix.

Genes and proteins for solute transport and sensing.

Genes and proteins for solute transport and sensing.

Three-dimensional hydrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic flow through porous media.

We report the results of a study of multiphase flow in porous media. A Darcy's law for steady multiphase flow was investigated for both binary and ternary amphiphilic flow. Linear flux-forcing relationships satisfying Onsager reciprocity were shown to be a good approximation of the simulation data. The dependence of the relative permeability coefficients on water saturation was investigated and showed good qualitative agreement with experimental data. Nonsteady-state invasion flows were investigated, with particular interest in the asymptotic residual oil saturation. The addition of surfactant to the invasive fluid was shown to significantly reduce the residual oil saturation.

Single-layer type microwave absorber made of magnetic-dielectric composite material

It has been shown experimentally in a single-layer microwave absorber that a matching frequency can be adjusted in the frequency range from 7.7GHz to 9.4GHz. A reflection loss above -40dB or more in maintained by changing the mixing ratio of magnetic and dielectric material in the composite. Complex relative permeability and permittivity coefficients were measured using a terminative short and open circuit method. Theoretical calculations clarified the relations among these constants, matching frequency and the reflection loss.

Evaluation of the Darcy's law performance for two-fluid flow hydrodynamics in a particle debris bed using a lattice-Boltzmann model

In the present paper, multiphase flow dynamics in a porous medium are analyzed by employing the lattice-Boltzmann modeling approach. A two-dimensional formulation of a lattice-Boltzmann model, using a D2Q9 scheme, is used. Results of the FlowLab code simulation for single phase flow in porous media and for two-phase flow in a channel are compared with analytical solutions. Excellent agreement is obtained. Additionally, fluid-fluid interaction and fluid-solid interaction (wettability) are modeled and examined. Calculations are performed to simulate two-fluid dynamics in porous media, in a wide range of physical parameters of porous media and flowing fluids. It is shown that the model is capable of determining the minimum body force needed for the nonwetting fluid to percolate through the porous medium. Dependence of the force on the pore size, and geometry, as well as on the saturation of the nonwetting fluid is predicted by the model. In these simulations, the results obtained for the relative permeability coefficients indicate the validity of the reciprocity for the two coupling terms in the modified Darcy's law equations. Implication of the simulation results on two-fluid flow hydrodynamics in a decay-heated particle debris bed is discussed.

Mechanistic Model of Steady-State Two-Phase Flow in Porous Media Based on Ganglion Dynamics

Recent experimental work has shown that the pore-scale flow mechanism during steady-state two-phase flow in porous media is ganglion dynamics (GD) over a broad and practically significant range of the system parameters. This observation suggests that our conception and theoretical treatment of fractional flow in porous media need careful reconsideration. Here is proposed a mechanistic model of steady-state two-phase flow in those cases where the dominant flow regime is ganglion dynamics. The approach is based on the ganglion population balance equations in combination with a microflow network simulator. The fundamental information on the cooperative flow behavior of the two fluids at the scale of a few hundred pores is expressed through the system factors, which are functions of the system parameters and are calculated using the simulator. These system factors are utilized by the population balance equations to predict the macroscopic behavior of the process. The dependence of the conventional relative permeability coefficients not only on the wetting fluid saturation Swbut also on the capillary number, Ca, the viscosity ratio κ the wettability (θ0 a, θ0 r), the coalescence factor, Co, as well as the porous medium geometry and topology is explained and predicted on a mechanistic basis. Sample calculations have been performed for steady-state fully developed (SSFD) and steady-state nonfully developed (SSnonFD) flow conditions. The number distributions of the moving and the stranded ganglia, the mean ganglion size, the fraction of the nonwetting fluid in the form of mobile ganglia, the ratio of the conventional relative permeability coefficients and the fractional flows are studied as functions of the system parameters and are correlated with the flow phenomena at pore level and the system factors.

Generalized relative permeability coefficients during steady-state two-phase flow in porous media, and correlation with the flow mechanisms

Generalized relative permeability coefficients during steady-state two-phase flow in porous media, and correlation with the flow mechanisms

Generalized relative permeability coefficients during steady-state two-phase flow in porous media, and correlation with the flow mechanisms

Generalized relative permeability coefficients during steady-state two-phase flow in porous media, and correlation with the flow mechanisms

Percolation model of two-phase equilibrium flow in a porous medium with microheterogeneous wettability

The percolation model of two-phase flow described in [1, 2] is used as a basis for examining the problem of the behavior of the characteristics of two-phase equilibrium flow in a porous medium when the capillaries have a radius distribution and differ with respect to the wettability properties of their surfaces. Analytic expressions describing the dependence of the relative phase permeability coefficients on the saturation of the medium by the displacing phase and the microinhomogeneous wettability parameters are obtained. A qualitative comparison shows the theoretical results to be consistent with the data of a direct numerical computer calculation of a grid model [3]. The effect of the microinhomogeneity parameters and the form of the capillary radius distribution function on the phase permeabilities is analyzed within the framework of the approach developed.

Heterogeneity effects on permeability-partition coefficient relationships in human stratum corneum.

The relationship between the permeability of solutes undergoing transport via the lipid pathway of the stratum corneum and the degree to which the same solutes partition into the stratum corneum has been explored by measuring the permeability coefficients and stratum corneum/water partition coefficients of a series of hydrocortisone esters varying in lipophilicity. Isolated human stratum corneum, used in both the permeability and the uptake experiments, was shown to resemble full-thickness skin in its overall resistance and selectivity to solute structure. As with full-thickness skin, delipidization destroys the barrier properties of isolated stratum corneum. Although a linear relationship is frequently assumed to exist between permeability coefficients and membrane/water partition coefficients, a log-log plot of permeability coefficients versus the intrinsic stratum corneum/water partition coefficients for the series of hydrocortisone esters studied is distinctly nonlinear. This nonlinearity arises from the fact that the transport of these solutes is rate limited by a lipid pathway in the stratum corneum, while uptake reflects both lipid and protein domains. From the relative permeability coefficients of 21-esters of hydrocortisone varying in acyl-chain structure, group contributions to the free energy of transfer of solute into the rate-limiting barrier microenvironment of the stratum corneum lipid pathway are calculate for a variety of functional groups including the -CH2-, -CONH2, -CON(CH3)2, -COOCH3, -COOH, and -OH groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and characteristics of the occluding junctions in a monolayer of a cell line (MDCK) derived from canine kidney.

On solid substrates MDCK, a cell line derived from normal dog kidney, forms a confluent monolayer that is studded with "blisters". Previous studies with this cell line suggest that these hemicysts develop as a result of active fluid accumulation between cell sheet and substratum. One factor that may determine when and how hemicysts appear only in localized sites is the interruption of occluding junctions in nonhemicyst areas. To study this possibility, we compared the permeability characteristics of the occluding junctions in hemicysts and in an uninterrupted monolayer of MDCK grown on a permeable support of collagen-coated nucleopore filter. The spontaneous electrical potential differences were small, without statistical differences between them. Relative ionic permeability coefficients were evaluated from the voltage deflections to imposed salt gradients or to a single ion substitution across both structures. The results showed that the relative permeability ratios for Na+, K+, choline+, and Cl- were the same in hemicysts and the uninterrupted monolayer. These and other results indicate that the junctional complex encircling the apical surface of a sheet of MDCK cells can provide an effective permeability barrier constituting a true occluding junction with the same properties in hemicyst and nonhemicyst areas.

Mn2+ Ionic Permeability and Conductance Properties of Maize Primary Root Epidermis

Summary The results of in vitro experiments carried out on the maize primary root epidermis with a view to studying the permeability and conductance properties of this tissue are detailed. The transepidermal potential ET was measured as it varied with external concentrations of MnCl2 in the bathing solution. Relative and absolute permeability coefficients, as well as the relative conductance for the measured ET and the corresponding concentration gradients, were determined. The membrane potential Em was calculated according to a modified formulation of the Goldman equation and the Nernst potential was determined for the appropriate concentration gradients used in measuring ET.

Discrimination of monovalent inorganic cations by "tight" junctions of gallbladder epithelium.

Relative permeability coefficients (P's) for Li+, Na+, K+, Rb+, Cs+, NH 4 + and Tl+ have been measured in gallbladders of several animal species. Small differences are observed among individual animals of the same species in theP values for a given ion. Individual variations inP values of different ions are closely correlated, permitting construction of so-called selectivity isotherms. Exposure to pH 4 reversibly shiftsP values along the same isotherms as those defined by individual variation. Changes in partial conductances with pH indicate that cation conductance is controlled by acidic sites with an apparent pK a value near 4.5, anion conductance by basic sites with an apparent pK a value below 3. Isotherms for rabbit gallbladder and bullfrog gallbladder are quite similar, and the small differences between them are probably attributable to a narrower permeation channel in rabbit in bullfrog. Permeability ratios for eight other epithelia with leaky “tight junctions” fall close to the isotherms for rabbit and bullfrog gallbladders. The observed isotherms, sequences, and pH-dependence of alkali cation permeability are strikingly consistent with Eisenman's interpretation that selectivity is controlled by site field strength. Variation inP Tl andP NH4 is also correlated with variation in site field strength. Comparison with isotherms or “selectivity fingerprints” for glass electrodes and macrocyclic carriers suggests that the permeation channel in gallbladder tight junctions is highly hydrated; and that sites in the gallbladder may possess net charge and may not be in a precisely regular spatial array.

The effect of vasopressin on the permeability of frog skin to cations

The effect of vasopressin on the permeability of isolated frog skin to some cations was studied by determining the permeability coefficients of K +, Cs + and Rb + in relation to that of Na +, with and without supramaximal doses of vasopressin. The relative permeability coefficients for Cs + and Rb + are much lower in the presence that in the absence of vasopressin, while for K + it remains unaltered.

The effect of secretin on electrical potential differences in the pancreatic duct

1. 1. Electrical potential differences (PD's) have been measured between the major pancreatic duct and blood of anesthetized cats during free flow of pancreatic juice and during perfusion of the duct with simple salt solutions. The measured PD's were corrected for junction potentials. 2. 2. During free flow the hormone secretin shifts the duct potential in the negative direction by 7 mV, approximately in phase with the secretin-stimulated juice flow. 3. 3. During perfusion secretin shifts the duct PD in the negative direction by about 3 mV, independent of the composition of the perfusion solution used. 4. 4. Relative ionic permeability coefficients for Na +, K +, Cl −, and HCO 3 − in pancreatic duct have been calculated from diffusion potentials and are unaffected by secretin. 5. 5. The ion fluxes stimulated by secretin are up the electrochemical gradient for HCO 3 −, down the gradient for Na +, K +, and Cl −. 6. 6. It is concluded that the effect of secretin on the pancreas is to stimulate active HCO 3 − secretion, as in the liver; and that the secretin-induced PD during free flow is due partly to a change in diffusion potential, partly to the direct effect of active ion transport.

Effects of pH and polyvalent cations on the selective permeability of gall-bladder epithelium to monovalent ions

1. 1. From the effect of pH on KCl diffusion potentials an effective titration curve is obtained for the membrane charges controlling ion selectivity in gall-bladder epithelium. The epithelium behaves as if it is negatively charged at physiological pH (K + and Na + more permeant than Cl −), has an isoelectric point near pH 3, and is positively charged at lower pH (Cl − more permeant than K + or Na +). This inversion of selectivity at low pH is completely reversible. 2. 2. The positive charges responsible for selective permeability to Cl − at low pH react with 1,5-difluoro-2,4-dinitrobenzene. 3. 3. The relative potencies of 17 polyvalent cations in increasing P Cl /P Na are compared, where P stands for relative permeability coefficients of the ions indicated. 4. 4. Low pH and high Ca 2+ concn. both decrease cation conductance and increase anion conductance. 5. 5. Protonation of membrane charges also affects selectivity among alkali cations: P Cs /P Na inverts, and P K /P Na decreases, at low pH. 6. 6. The results are related to theories analysing inter-cation specificity in terms of the field strength of membrane charged groups.

EFFECTS OF SOME COMMON IONS ON THE TRANSRETINAL DC POTENTIAL AND THE ELECTRORETINOGRAM OF THE ISOLATED FROG RETINA

1. In order to measure changes in the transretinal dc potential and the ERG, the isolated bullfrog's retina deprived of the pigment epithelium placed as a septum separating the modified Conway solution in the apparatus.2. From diffusion potentials between non-identical solutions, the relative permeability coefficients were: PNa: PK: Pcholine PCl: PSO4=0.33: 1.00: 0.27: 0.29: 0.11.3. The ‘half-times’ of the diffusion potential transients produced due to increasing the potassium concentration was 2.2 times longer for the vitreous surface than for the receptor surface. This suggests that the vitreous surface has a indiscriminate retarding force to potassium diffusion.4. Low sodium or high potassium solution on the receptor side induced the reduction in the ERG, while no change on the vitreous side. The reduction in the ERG with a low sodium solution related to the log of the sodium concentration.5. Decreasing chloride concentration on the receptor side to 15 or 0 mM, the amplitude of the ERG was reduced, whereas on the vitreous side it was increased. These light responses could be due to a direct effect of lack of chloride in the bathing solution rather than to a reduction of calcium ions or the effect of polarizing current across the retina.6. High potassium solution, azide or ouabain on the receptor side causedspontaneously a slow oscillatory dc potential change resembling Leao's spreadingcortical depression, whereas when either one side of the retina was exposedto a low chloride solution, the slow oscillatory potential induced following alight stimulation. On the basis of these results it is proposed that the slowoscillatory potential is the response of the scleral portion of the MULLER cells.

The effect of membrane fixed charges on diffusion potentials and streaming potentials.

1. Electrical potential differences (p.d.'s) have been measured across an in vitro preparation of rabbit gall-bladder.2. When the gall-bladder separates identical bathing solutions, the p.d. is always zero, regardless of the composition of the bathing solution. Hence the gall-bladder is symmetrical: i.e. the mucosal and serosal cell membranes have the same relative permeability coefficients.3. Osmotic water flow causes streaming potentials of up to 20 mV, of a sign indicating greater permeability to cations than to anions.4. At constant osmolarity, streaming potentials increase slightly with NaCl concentration. Streaming potentials decrease considerably with changes in osmolarity resulting from changes in NaCl concentration.5. Diffusion potentials resulting from electrolyte concentration gradients are fitted well by the constant-field equation with the relative permeability coefficients P(Na) = 1.00, P(Cl) = 0.33, P(K) = 2.3. These permeability coefficients are independent of osmolarity and of salt concentration.6. Relative to 0.25 mM-Ca, 5 mM-Ca reduces streaming potentials by 40%, NaCl diffusion potentials by 62%, and potassium diffusion potentials by 43%.7. The aqueous channels through which water and electrolytes traverse the cell membranes of the gall-bladder contain negative fixed charges, which are blocked by Ca. The physiological significance of the charges may be to reduce chloride permeability and thereby to increase the effectiveness of the gall-bladder in concentrating bile.8. The effect of pH, and analogy with surface charges of other cells, suggest that the charges are organic acids of low pK(a).

Effect of External K, NH4, Na, Ca, Mg, and H Ions on the Cell Transmembrane Electropotential of Avena Coleoptile

A number of studies have shown that an electropotential difference, PD, of about 100 mv (interior negative), is present across plant cell membranes (2, 3, 7, 8, 10, 11, 13, 21), similar to that across animal cell membranes. Thus, if minerals move through cell membranes as ions, they are subject not only to concentration gradients but also to electrical fields. For precise evaluation of the energy relationships in ion accumulation and active ion transport by cells the electropotential gradient as well as the chemical gradient must be known (4, 5). Active ion transport, requiring metabolic energy, is defined as transport against the electrochemical activity gradient (4, 5). Cases are known in which ion accumulation takes place without the expenditure of metabolic energy (5, 18). The use of the Nernst equation in elucidating the fundamental relationships of electropotential differences to ionic concentration gradients across plant cell membranes has been discussed recently in detail by Dainty (5) and by Briggs, Hope, and Robertson (4). The results of similar studies of animal cells (12, 16, 19) and of giant cells of algae (2, 11, 13, 21) show that the resting electropotentials have an approximate quantitative relationship to the concentration gradient at equilibrium of the ions K+, Na+, and Cl-. This relationship is more closely approached when consideration is given to the relative permeability coefficients of these ions as in Goldman's modification (9) of the Nernst equation. This suggests that the resting potential is diffusional in origin, that it may be primarily a function of the relatively few more rapidly permeating ions, and that K+, in particular, may have a predominant effect. Previous reports have shown that oat, corn, and pea seedling tissue cells, exhibit a transmembrane PD which is influenced by external K+ concentration in the direction predicted by the Nernst equation (8). However, the effect on these plant cell PD's of ions other than K+ has not been evaluated. The present report deals with a limited survey of the effect on PD of manipulating the ion concentration gradients by altering the external concentration. This paper gives details of the results mentioned in an earlier brief report (10).