Apparent Transference Number Research Articles

Unveiling the transport properties of protic ionic liquids: Lithium ion dynamics modulated by the anion fluorine reservoir

Protic ionic liquids (PILs) show great potential as electrolyte components for energy storage devices. A comprehensive understanding of their transport properties must be achieved to optimize the design of safer and efficient electrolytes. This study focuses on a series of PILs based on the DBUH+ cation (protonated 1,8-diazabicyclo[5,4,0]‑undec-7-ene superbase) and three anions derived from strong acids: TFO− (triflate), IM14− (perfluorobutyl-trifluoromethylsulfonylimide) and TFSI− (bis(trifluoromethylsulfonyl)imide). Neat PILs and PILs doped with LiTFO, LiIM14, and LiTFSI were studied using temperature-dependent NMR diffusion and relaxation techniques. The ionicity of these systems was also evaluated. Results revealed that the dynamic behaviour of lithium ions, as well as ionicity, strongly depend on the structural features of the anions, particularly in the case of IM14−, whose main feature is the uneven distribution of the fluorinated sidegroups. The 19F relaxation rates in IM14− provide insights into the rotational reorientation of that anion. DBUH-IM14 exhibited diffusion coefficients lower than the expected ones on the basis of its viscosity, likely due to fluorophilic intermolecular interactions involving the fluorinated terminal groups. The presence of Li+ in the DBUH-IM14 electrolyte led to unexpected and relatively faster translational mobility of Li+ ions, resulting in a higher lithium apparent transference number. However, the trends observed in ionicity indicate a more complex interplay between intermolecular interactions and ion correlations. While DBUH-TFSI showed minimal effect of Li+ addition, DBUH-TFO and DBUH-IM14 exhibited a significant decrease in ionicity, possibly attributed to strong interactions between ions.

Structure and ion transport in super-concentrated water-in-salt electrolytes: Insights from molecular dynamics simulations

Water-in-salt electrolyte (WISE) systems hold promise as materials for high performance, more reliable and affordable, energy storage devices including batteries and supercapacitors. However, the structure and ion dynamics in these systems is significantly different from those of aqueous electrolytes and are poorly understood. Here, we present molecular dynamics investigation of water-in-salt electrolyte materials having pure as well as eutectic mixtures of Li-NTF2, and Li-MM3411 salts at several concentrations. We find the existence of small water clusters such as dimers and trimers even at extremely high salt concentrations, but not pockets of bulk water molecules. We find that the water molecules are bound to the cation as well as anion at extremely high salt concentrations. It is found that Li ions display a variety of solvation environments in super concentrated electrolyte solutions depending on the salt and its concentration in water. Our simulation results suggests that ion transport follows a solvent-assisted Li-ion diffusion mechanism whereby Li ion diffuses along with the water molecules, with the Li-ions hopping from one anion site to the other. The cation transport number in WISE systems can be regulated by adding small amount of another salt; for example, the transference of WISE materials Li-NTF2 salt can be improved by adding small amount Li-MM3411 salt. Further, we show that there exists an optimal salt concentration in water, at which high apparent transference number for Li+ as well as high ionic conductivity can be achieved. These observations will provide a guidance for the design of new electrolyte systems and interphases with consequences for accelerating the development of batteries and supercapacitors with enhanced energy density and cycling stability.

Measuring Lithium-Ion Transport Properties in Electrolytes Via in Situ Infrared Spectroscopy

Electrolyte transport capability is a critical measure of battery function for both current Li-ion technology and chemistries beyond Li-ion. Ion transport plays a vital role in fast-charging, lithium plating, and performance under extreme temperature and cycling conditions. Though traditional electrolytes have been widely studied, current experimental methods do not allow for simple measurements of transport properties, often requiring large electrolyte volumes, long experiment times, and a dilute assumption. In this research, we developed analytical models that accurately predict apparent diffusion coefficient and transference number from numerical models of electrolyte ion concentrations in a lithium symmetric cell. The first analytical model utilized one-dimensional diffusion to predict the transient response of lithium concentration in the bulk electrolyte to an applied current. The second analytical model predicted lithium-ion concentration decay in a Li/Li cell at the electrode surface following a brief current pulse. The analytical models were used to fit numerical finite difference simulations of Li/Li cell performance to predict transport properties. This result suggests that current pulse methods can be applied to experimentally ascertain electrolyte diffusion properties. A new diagnostic is under development for characterizing electrolyte transport properties, diffusion coefficient and transference number, using the current pulse method applied to an in situ symmetric Li/Li cell. This diagnostic utilizes Fourier transform infrared spectroscopy and attenuated total reflectance to measure transport properties with low volumes of electrolyte and short experiment times. This capability may enable simple and rapid measurement of transport properties for electrolyte candidate screening and enrich broader understanding of electrolyte transport.

The electrochemical measurement of salt diffusion coefficient, apparent cation transference number and ionic conductivity for a thin-film electrolyte.

Further development of the electrochemical measurement procedure, namely the Symmetric Polarization Procedure (SPP), is described. The SPP allows for an additional verification of measurement assumptions through a quick and simple inspection of a symmetry between the procedure outcomes. It also improves the precision of estimated transport properties. A considerable emphasis was also put on detailed outcomes analysis. In particular, a newly developed approach to the analysis of restricted diffusion data is proposed. This approach is based on a power law which is a common form for the rate equation, therefore it allows for a precise estimation of the salt diffusion coefficient and, innovatively, the diffusion domain. Importantly, as a result of this approach, the subdiffusive-like response is recognized in every electrolyte examined herein. The viscoelastic relaxation of polymer matrix is given as most probable cause of such response. Additionally, four approaches that lead to a quantification of the apparent cation transference number are also extensively discussed. It has been demonstrated, how a knowledge about the salt diffusion coefficient, the apparent cation transference number and the ionic conductivity can be used to evaluate the electrochemical performance of an electrolyte. It is also shown, how these properties can be utilized to approximate the diffusion-limited current and the deviation from Nernst-Einstein equation.

Water-In-Salt LiTFSI Aqueous Electrolytes (2): Transport Properties and Li+ Dynamics Based on Molecular Dynamics Simulations.

The transport properties of water-in-salt lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) aqueous electrolytes were studied using classical molecular dynamics (MD) simulations. At high salt concentrations of 20 m, the calculated viscosity, self-diffusion coefficients, ionic conductivity, the inverse Haven ratio, and the Li+ apparent transference number all agree with previous experimental results quantitatively. Furthermore, analyses show that the high apparent transference number for Li+ is due to the fact that the dynamics of TFSI- decrease more quickly with increasing salt concentration than the dynamics of Li+ ions due to the formation of a TFSI- network. In addition, it was shown that the conduction of Li+ ions through the highly concentrated electrolyte occurs mainly via a hopping mechanism instead of a vehicular mechanism hypothesized in earlier studies of this system.

Negative effective Li transference numbers in Li salt/ionic liquid mixtures: does Li drift in the "Wrong" direction?

The electrophoretic mobilities μ of all ion species in the lithium salt/ionic liquid mixtures LiTFSA/EmimTFSA and LiBF4/EmimBF4 are determined by 1H, 19F and 7Li electrophoretic NMR. The average drift direction of Li is identical to that of the anions TFSA- or BF4-. This proves a correlated ion motion of Li with the anions in negatively charged Li-containing clusters in both systems. The effective charge of these clusters is determined as -1, or -2 in the system with TFSA or BF4, respectively, pointing at the existence of [Li(TFSA)2]- or [Li(BF4)3]2-. This behavior is described by a negative effective transference number of Li, resulting in a negative contribution of Li ions to the overall conductivity. Li effective transference numbers are in the range of -0.04 to -0.02, depending on Li salt concentration and anion type. Transference numbers thus clearly deviate from apparent transference numbers estimated from diffusion coefficients, as an effect of a vehicular transport mechanism. This has important implications for the mechanism of Li mass transport in Li ion batteries as the drift of charged clusters has to be overcompensated by diffusive mass transport of neutral, Li-containing aggregates.

Direct relations between ion diffusion constants and ionic conductivity for lithium electrolyte solutions

Lithium cation and anion diffusion constants (DLi and DAnion) are plotted versus ionic conductivity (σ) (σ–D relation) for lithium organic electrolyte solutions which are important to investigate Li secondary batteries. Lithium salts studied are LiPF6, LiBF4, LiN(SO2CF3)2 (LiTFSA), LiN(SO2C2F5)2 (LiBETI), LiC4BO8 (LiBOB), LiSO3CF3 and Li2B12F12. Main organic solvents are propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (GBL), diethyl carbonate (DEC), four glymes and polyethylene glycol (PEG) dimethyl ethers of average molecular weights of 400 and 1,000. Mixing effects of two solvents are shown for EC-DEC-LiPF6 systems. In total, about 20 organic electrolyte solutions were studied. In addition, for six binary ionic liquid systems, σ–D relations are plotted. Values for the degree of apparent ion dissociation (α) were calculated from the DLi, DAnion and σ using the Nernst-Einstein (NE) relation and are plotted against σ (σ–α relation). The number of charge-carrying ions (Ncarrier) was estimated from the α and salt concentration, and plotted versus σ (σ-Ncarrier relation). To estimate the velocity of ions, the σ–Dsolvent relations are plotted. Also, the apparent lithium transference number (tLi) obtained simply from the DLi and Danion values are plotted versus σ (σ −tLi relation). While we have already reported all the data in our previous papers, we did not plot directly the ion diffusion constants and other parameters versus ionic conductivity. In this paper, the importance of the direct relations of σ–D, σ–α, and σ-Ncarrier is demonstrated to understand functions of lithium electrolyte solutions.The numerical data are freely available in Supplementary Information (SI), covering broad aspects of the fundamental and practical lithium electrolyte solution systems. We believe that they will contribute to the research and development for next generation Li battery systems.

Operando X-ray Tomographic Microscopy Imaging of HT-PEFC: A Comparative Study of Phosphoric Acid Electrolyte Migration

Synchrotron based X-ray tomographic microscopy was used to image the redistribution of phosphoric acid in HT-PEFC due to electrolyte migration from cathode to anode. The acid migration rate, transference number of the hydrogen phosphate ion and flooding of the anode gas diffusion layer (GDL) was analyzed for MEAs with different membrane acid doping levels (24–36 mgcm−2) and membrane materials (imbibed m-polybenzimidazole (PBI) and polyphosphoric acid (PPA) processed p-PBI). The most influential factors for the acid migration rate are current density and the amount of free acid in the membrane. High doping level of the membrane and current density above 0.4 A cm−2 significantly increase the migration rate. From the migration rates apparent transference numbers for the hydrogen phosphate anions in the order 10−5 to 10−4 are calculated at the high current densities. Besides the membrane properties, also the influence of the microstructure of the porous transport layers was analyzed. Most probably cracks in the catalyst and microporous layers facilitate the migration of acid into the anode GDL.

Boosting the voltage of a salinity-gradient-power electrochemical cell by means of complex-forming solutions

We report experiments on a concentration cell with zinc electrodes and ZnCl2 solutions at different concentrations, separated by a porous diaphragm. The cell is aimed at the conversion of the free energy associated to the concentration difference into electrical energy, for renewable and clean energy applications. Usually, the diffusion of the solute across the diaphragm constitutes a waste of free energy, which impairs the voltage generation of the concentration cell with respect to other well-known techniques that work quasi-reversibly, such as reverse electrodialysis or the “mixing entropy battery.” Quite surprisingly, we find that the voltage produced by our concentration cell is significantly higher than the voltage obtained with the other quasi-reversible techniques. We show that the surplus voltage comes from the active transformation of the mixing free energy into electrical energy performed by the liquid junction, and we show the connection with the negative apparent transference number of the zinc ion. This fortunate consequence of using ZnCl2 solution is ultimately related to the formation of complexes. We present the results of a cell for power production, which has excellent performances with respect to known salinity-difference-power methods.

Enhanced Lithium Transference Numbers in Ionic Liquid Electrolytes

Ion transport processes in mixtures of N-butyl- N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) and lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) were characterized by ac impedance spectroscopy and pulsed field gradient NMR. Molar ratios x = n Li-TFSI/( n Li-TFSI + n BMP-TFSI) up to 0.377 could be achieved without crystallization. From the bulk ionic conductivity and the individual diffusion coefficients of cations and anions we calculate the Haven ratio and the apparent lithium transference number. Although the Haven ratio exhibits typical values for ionic liquid electrolytes, the maximal apparent lithium transference number is higher than found in other recent studies on ionic liquid electrolytes containing lithium ions. On the basis of these results we discuss strategies for further improving the lithium transference number of such electrolytes.

Amphiphilic Polymer Gel Electrolytes. 4. Ion Transport and Dynamics As Studied by Multinuclear Pulsed Field Gradient Spin-Echo NMR

The transport dynamics in gel electrolytes based on amphiphilic polymers was found to be faster than in gel electrolytes based on corresponding nonamphiphilic polymers. The amphiphilic polymer studied was a polymethacrylate grafted with fluorocarbon and (EO)9 side chains, and the nonamphiphilic one was a polymethacrylate carrying only (EO)9 side chains. Self-diffusion coefficients of gel electrolytes based on the two polymers with different contents of 1 M lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) salt in γ-butyrolactone were determined by 1H, 19F, and 7Li pulsed field gradient spin-echo NMR spectroscopy. The polymer self-diffusion coefficients showed that the amphiphilic polymer molecules diffused faster than the nonamphiphilic ones and seemed more intramolecularly aggregated than intermolecularly. At electrolyte contents above 43 wt %, the ion conductivity of the amphiphilic polymer gel electrolytes was higher than for the corresponding gel based on the nonamphiphilic polymer under identical conditions, as measured by impedance spectroscopy. Moreover, the lithium ion diffusion coefficient in the amphiphilic gel electrolytes was found to be significantly higher than that for corresponding gels based on the nonamphiphilic polymer. The higher ethylene oxide content of the nonamphiphilic polymer decreased the mobility of the lithium ions due to cooperative coordination of lithium ions by ether oxygens in comparison with γ-BL. The TFSI anion diffusion was however approximately the same in the two gel systems. Consequently, the apparent lithium transference number (τ+) of the amphiphilic gels was higher by almost a factor of 3 as compared to that of the gels based on the nonamphiphilic polymer. A splitting of the TFSI signal in the 19F NMR spectra suggested that the TFSI anions in the amphiphilic polymer gels were partly present in a solvent-rich environment and partly associated with the aggregates formed by the fluorinated side chains. This kind of splitting was not observed in the spectra of the gels based on the nonamphiphilic polymer. The association of TFSI anions to the aggregated fluorinated side chains may thus also play a role in increasing the value of τ+ for the amphiphilic polymer gels.

Synthesis, Characterization, and Ion-Conductive Behavior in an Organic Solvent and in a Polyether of a Novel Lithium Salt of a Perfluorinated Polyimide Anion

To achieve highly conductive polymer electrolytes with a controllable ionic transference number, a novel polymeric lithium salt was synthesized and characterized. The novel lithium salt of a perfluorinated polyimide anion, poly(5-oxo-3-oxy-4-trifluoromethyl-1,2,4-pentafluoropentylene sulfonylimide lithium) (LiPPI), has a polyanionic backbone with a repeating unit resembling highly dissociable, thermally and electrochemically stable imide salts, such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The ion-conductive behavior of LiPPI in an organic solvent and in a polyether was extensively studied by using pulse-gradient spin-echo NMR, in addition to differential scanning calorimetry, complex impedance measurement, and dynamic mechanical analysis. Solutions of LiPPI in ethylene carbonate (EC) exhibited a high degree of dissociation and high ionic conductivity, and the self-diffusion coefficient of the anion was lower than that of the cation. Solvent-free polymer electrolytes were prepared by dissolving LiPPI in a matrix polyether to afford a compatible polymer alloy, and the ionic conductivity of the new polymer alloy electrolytes reached ca. 10-5 S cm-1 at 30 °C. Although the lithium ionic transference number in the organic electrolyte solution was approximately the same as that of LiTFSI in EC, the polymer alloy electrolyte gave an apparent transference number higher than 0.7, which was considerably higher than that of LiTFSI in the same polyether.

Electron–hole conduction in Pr-doped Ce(Gd)O 2− δ by faradaic efficiency and emf measurements

Non-negligible electrode polarisation in faradaic efficiency and emf electrochemical cells used for transport number determination results in apparent ion transference numbers which are lower than the true values. However, appropriate modifications of these techniques combined with use of electrodes having a high polarisation resistance, enable a precise determination of even minor electronic contributions to the total conductivity of solid electrolytes. Experimental modification of the faradaic efficiency method, taking into account the electrode polarisation resistance, is proposed and verified using Ce 0.80Gd 0.18Pr 0.02O 2− δ ceramics. Substitution of 2% gadolinium cations in the lattice of Ce 0.80Gd 0.20O 2− δ solid electrolyte with praseodymium was found to increase the p-type electronic conductivity by 2.5–4 times, while the activation energy for the electron–hole transport decreases from 145 to 125 kJ mol −1. The oxygen ion transference numbers of Ce 0.80Gd 0.18Pr 0.02O 2− δ in air vary in the range 0.996–0.970 at 873–1223 K, decreasing with increasing temperature. No significant effect of co-doping with praseodymium on the ionic conductivity, crystal lattice and thermal expansion of ceria solid electrolyte was found.

Troglitazone Stimulates Basolateral Rheogenic Na+/HCO–3 Cotransport Activity in Rabbit Proximal Straight Tubules

Thiazolidinedione derivatives, new insulin-sensitizing antidiabetic agents, are expected to have potential clinical use. Since these drugs cause edema in a variable proportion of patients, we examined whether troglitazone (Tro) has direct action on Na⁺ transport of rabbit proximal straight tubule perfused in vitro. For this purpose, we measured basolateral membrane voltage (V_B) by conventional microelectrode techniques and intracellular pH (pH_i) by microscopic fluorescence spectrophotometry with a pH-sensitive fluorescent dye, 2’, 7’-bis-2-carboxyethyl-5-carboxyfluorescein. Tro at 50 µM in the bath significantly depolarized both transepithelial voltage and V_B. To examine whether the basolateral rheogenic Na⁺/HCO^–₃ cotransport activity is affected by Tro, we observed V_B deflection upon abrupt 10-fold decrease in bath HCO^–₃ in the absence and presence of Tro. The apparent transference number of HCO^–₃ (t_HCO3), as calculated from the V_B deflection, was significantly greater in the presence of Tro (50 µM) than that seen in its absence. Tro caused cell acidification and increased the intracellular acidification rates (dpH_i/dt) upon abrupt 10-fold decreases in bath HCO^–₃ and Na⁺ concentrations. The stimulatory effects of Tro on t_HCO3 and dpH_i/dt were dose dependent between 5 and 50 µM, but they were unaffected at 0.5 µM. From these results, we conclude that Tro acts on the proximal straight tubule and stimulates the basolateral rheogenic Na⁺/HCO^–₃ cotransport activity. The stimulatory action of Tro may partly account for edema formation.

Effects of cumene hydroperoxide on cellular cation composition in frog kidney proximal tubular cells

Effects of cumene hydroperoxide were studied on the peritubular membrane potential and cellular cation composition in frog kidney proximal tubular cells. After perfusion of isolated frog kidneys for 30 min with 1.3×10 −4 mol l −1 cumene hydroperoxide Ringer solution, the peritubular membrane potential gradually declined. The ouabain-like effects were demonstrated on cell Na and K activities after 1 h of perfusion with cumene hydroperoxide. The peritubular apparent transference number for potassium was decreased. Intracellular pH was not altered in the presence of cumene hydroperoxide. Intracellular free Ca 2+ concentration increased slowly and moderately. The concentration of the malondialdehyde in the kidney homogenates, measured as an index of lipid peroxidation, was increased. A previously observable effect of cumene hydroperoxide on the peritubular membrane potential was prevented by oxygen radical scavengers.

Measurement of the apparent lithium ion transference number and salt diffusion coefficient in solid polymer electrolytes

Measurements of the apparent cation transference number of a solid polymer electrolyte by a voltammetric technique are compared with results from the steady-state dc polarization method. The combination of measurements made at a microelectrode and at a macroelectrode, performed in the absence of supporting electrolyte, yields both the apparent transference number θ, and the salt diffusion coefficient D. Lithium cationic transference numbers in a series of macroscopically solid gels were determined as a function of salt concentration.

The membrane potential of vestibular dark cells is controlled by a large Cl − conductance

The K + secretory epithelium of the vestibular labyrinth (dark cells) was impaled with glass microelectrodes in order to test the hypothesis that it contains a large Cl − conductance. In the first series of experiments, the short-circuited epithelium was perfused on both sides by a solution containing 150 mmol/l Cl −. The membrane voltage (PD) was −18 ± 1 mV ( N = 101), showed a Gaussian distribution, and the estimated input resistance of the cell (R ‘cell’) was 17 ± 3 MΩ . The PD responded to 10 −4 mol/l ouabain with a depolarization, suggesting the presence of a (Na + + K +)-ATPase. The PD responses to Cl − steps yielded an apparent transference number t Cl = 0.34 ± 0.03 ( N = 65) and those to K + steps yielded a t K = 0.16 ± 0.01 ( N = 48). In the second series of experiments, cells presumed to be Cl −-depleted were impaled in Cl −-free solutions. The distribution of the PD was not Gaussian; PDs as negative as −90 mV were observed. Cells with a highly negative PD also had a high R ‘cell’. With the addition of Cl − the PD collapsed to −19 ± 1 mV and R collapsed to 16 ± 3 MΩ (N = 145) which are not significantly different from values obtained in the first series of experiments when cells were impaled in a solution containing 150 mmol/l Cl −. Alternating the bath perfusate between Cl −-free and Cl −-containing solutions led to large PD transients. Cl −-induced PD transients could be mimicked by other anions suggesting an ion selectivity of Cl − > Br − > NO 3 − > I − ⪢ glutamate − = isethionate − = gluconate − . Cl −-induced PD transients could not be abolished by a blocker of the Na +/Cl −/K + cotransporter, 10 −4 mol/l piretanide ( N = 5); by a blocker of various anion transport systems, 10 −3 mol/l 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid (SITS: N = 2); or by several blockers of epithelial Cl − channels, 10 −4 mol/l 5-nitro-2(3-phenylpropylamino)-benzoic acid (NPPB; N = 2), and 10 −4 mol/l dichloro-di-phenyl-amine-2-carboxylic acid (DCDPC; N = 2). In a solution containing 15 mmol/l Cl − the apparent transference numbers were t Cl = 0.56 ± 0.03 ( N = 19) and t K = 0.44 ± 0.02 ( N = 66). The PD responses to K + steps were not abolished by the K + channel blockers barium, quinidine or TEA suggesting that the observed PD deflections were only partly due to a K + conductance and that the apparent t K is overestimating the contribution of the K + conductance. The response to piretanide was variable. However, in a solution containing 15 mmol/l Cl − hyperpolarizations up to −80 mV were observed. These results demonstrate that vestibular dark cells contain a dominating Cl − conductance and suggest that this Cl − conductance is a manifestation of a Cl − channel.

Effect of protamine on ion conductance of ascending thin limb of Henle's loop from hamsters

To evaluate the contribution of paracellular shunt pathway in ascending thin limb (ATL) of hamsters, we examined the effect of protamine, a selective blocker of paracellular conductance, on salt-diffusion voltage (dVT) and transmural resistance (RT) during in vitro microperfusion. Lumen-negative dVT generated on reduction of lumen NaCl concentration was increased further from -7.3 +/- 0.5 to -10.3 +/- 0.7 mV when 300 micrograms/ml protamine was added to the lumen, and calculated Na+/Cl- permeability ratio was decreased from 0.46 +/- 0.03 to 0.31 +/- 0.03. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin returned the dVT toward the control level. The effect of protamine was dose dependent from 30 to 300 micrograms/ml. Protamine also exerted its effect from the bath, and the effect was inhibited by heparin either from the lumen or from the bath. The inhibitory effect was almost the same when the orientation of imposed NaCl gradient was reversed. Inhibition of transcellular Cl- transport with 0.1 mM 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) in the bath caused lumen-positive dVT. This voltage was decreased significantly by protamine. Protamine markedly decreased the apparent transference number for Na+ but slightly increased the value for Cl-. Transmural cable analysis showed that 300 micrograms/ml protamine added to the lumen increased RT from 0.59 +/- 0.10 to 1.20 +/- 0.20 omega.cm2, with the effect being reversed by 30 U/ml heparin.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of protamine on ion conductance of upper portion of descending limb of long-looped nephron from hamsters

To estimate the contribution of paracellular shunt pathway to the cation-selective permeability in the upper portion of the descending limb of long-looped nephron (LDLu) of hamsters, we observed the effect of protamine on salt-diffusion voltage (delta VT) and transmural resistance (RT). delta VT generated on reduction of lumen NaCl concentration was decreased from 12.0 +/- 1.4 to 7.3 +/- 1.2 mV when 100 micrograms/ml protamine were added to the lumen. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin reversed the delta VT toward the control level. The effect of protamine was dose dependent in the range from 3 to 1,000 micrograms/ml. Protamine was without effect from the bath. Studies on single salt dilution voltage revealed that 100 and 300 micrograms/ml protamine inhibited relative Na+ to Cl- permeability from 4.03 +/- 0.38 to 2.14 +/- 0.21 and from 3.75 +/- 0.37 to 1.36 +/- 0.09, respectively. Protamine markedly decreased the apparent transference number for Na+ but slightly increased the value for Cl-. Protamine also inhibited permeabilities for K+, Rb+, and Li+ relative to Cl-, indicating that the inhibitory effect of protamine was not confined to Na+ but was generalized to cations. Transmural cable analysis showed that 100 micrograms/ml protamine increased RT from 14.0 +/- 1.1 to 19.3 +/- 1.2 omega.cm2, with the effect being reversed by 30 U/ml heparin. Because the effect of protamine on RT was unaffected by ouabain in the bath, changes in RT may mainly represent those of the paracellular shunt resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Volume regulation and intracellular calcium in the rabbit proximal convoluted tubule

The hypothesis that an increase of calcium leads to activation of calcium-activated ionic conductances during cell swelling was examined in the isolated perfused proximal convoluted tubule of the rabbit. Reduction of bath and luminal osmolality by 90 mosmol/kgH2O caused the cells to swell by 23.6 +/- 1.5% (n = 5) and intracellular calcium to rise from 227 +/- 35 to 347 +/- 60 nM (n = 6). Both these increases were transient, with volume decreasing to 5.5 +/- 1.2% above control and intracellular calcium concentration decreasing to 272 +/- 46 nM after 5-9 min. The addition of glucose and alanine to the tubule lumen to increase transcellular sodium transport caused a sustained increase in cell volume of 15.6 +/- 3.4% (n = 4). In parallel experiments, no significant increase in intracellular calcium concentration was observed. Addition of 1 microM of the calcium ionophore, ionomycin, reversibly increased intracellular calcium by 224 +/- 60 nM from a control value of 301 +/- 29 nM (n = 7) and reversibly depolarized the basolateral membrane by 3.6 +/- 0.9 mV (n = 5). However, there was no initial increase in the apparent transference number for potassium or chloride and no significant change in cell volume. We conclude from these observations that the sustained increase in basolateral potassium conductance observed when cells are swollen by hypotonicity or increased sodium transport (J. S. Beck and D. J. Potts. J. Physiol. Lond. 425: 369-378, 1990) is not due to a calcium-activated potassium conductance.