Ion Secretion and Isotonic Transport in Frog Skin Glands

The aim of this study was to clarify the mechanism of isotonic fluid transport in frog skin glands. Stationary ion secretion by the glands was studied by measuring unidirectional fluxes of ²⁴Na⁺, ⁴²K⁺, and carrier-free ¹³⁴Cs⁺ in paired frog skins bathed on both sides with Ringer's solution, and with 10⁻⁵ m noradrenaline on the inside and 10⁻⁴ m amiloride on the outside. At transepithelial thermodynamic equilibrium conditions, the ¹³⁴Cs⁺ flux ratio, J ^out _Cs/J ⁱⁿ _Cs, varied in seven pairs of preparations from 6 to 36. Since carrier-free ¹³⁴Cs⁺ entering the cells is irreversibly trapped in the cellular compartment (Ussing & Lind, 1996), the transepithelial net flux of ¹³⁴Cs⁺ indicates that a paracellular flow of water is dragging ¹³⁴Cs⁺ in the direction from the serosal- to outside solution. From the measured flux ratios it was calculated that the force driving the secretory flux of Cs⁺ varied from 30 to 61 mV among preparations. In the same experiments unidirectional Na⁺ fluxes were measured as well, and it was found that also Na⁺ was subjected to secretion. The ratio of unidirectional Na⁺ fluxes, however, was significantly smaller than would be predicted if the two ions were both flowing along the paracellular route dragged by the flow of water. This result indicates that Na⁺ and Cs⁺ do not take the same pathway through the glands. The flux ratio of unidirectional K⁺ fluxes indicated active secretion of K⁺. The time it takes for steady-state K⁺ fluxes to be established was significantly longer than that of the simultaneously measured Cs⁺ fluxes. These results allow the conclusion that — in addition to being transported between cells — K⁺ is submitted to active transport along a cellular pathway.Based on the recirculation theory, we propose a new model which accounts for stationary Na⁺, K⁺, Cl⁻ and water secretion under thermodynamic equilibrium conditions. The new features of the model, as compared to the classical Silva-model for the shark-rectal gland, are: (i) the sodium pumps in the activated gland transport Na⁺ into the lateral intercellular space only. (ii) A barrier at the level of the basement membrane prevents the major fraction of Na⁺ entering the lateral space from returning to the serosal bath. Thus, Na⁺ is secreted into the outside bath. It has to be assumed then that the Na⁺ permeability of the basement membrane barrier (P ^BM _Na) is smaller than the Na⁺ permeability of the junctional membrane (P ^JM _Na), i.e., P ^JM _Na/P ^BM _Na > 1. The secretory paracellular flow of water further requires that the Na⁺ reflection coefficients (σ_Na) of the two barriers are governed by the conditions, σ^BM _Na > 0, and σ^BM _Na > σ^JM _Na. (iii) Na⁺ channels are located in the apical membrane of the activated gland cells, so that a fraction of the Na⁺ outflux appearing downstream the lateral intercellular space is recirculated by the gland cells. Based on measured unidirectional fluxes, a set of equations is developed from which we estimate the ion fluxes flowing through major pathways during stationary secretion. It is shown that 80% of the sodium ions flowing downstream the lateral intercellular space is recycled by the gland cells. Our calculations also indicate that under the conditions prevailing in the present experiments 1.8 ATP molecule would be hydrolyzed for every Na⁺ secreted to the outside bath. Received: 30 January 1996/Revised: 12 March 1996     

Sodium Recirculation and Isotonic Transport in Toad Small Intestine

Isolated small intestine of toad (Bufo bufo) was mounted on glass tubes for perfusion studies with oxygenated amphibian Ringer's solution containing glucose and acetate. Under open-circuit conditions (V _t =−3.9 ± 1.8 mV, N= 14) the preparation generated a net influx of ¹³⁴Cs⁺. The time course of unidirectional ¹³⁴Cs⁺-fluxes was mono-exponential with similar rate constants for influx and outflux when measured in the same preparation. The flux-ratio was time invariant from the beginning of appearance of the tracers to steady state was achieved. Thus, just a single pathway, the paracellular pathway, is available for transepithelial transport of Cs⁺. From the ratio of unidirectional Cs⁺-fluxes the paracellular force was calculated to be, 18.2 ± 1.5 mV (N= 6), which is directed against the small transepithelial potential difference. The paracellular netflux of cesium ions, therefore, is caused by solvent drag. The flux of ¹³⁴Cs⁺ entering and trapped by the cells was of a magnitude similar to that passing the paracellular route. Therefore, independent of the convective flux of ¹³⁴Cs⁺, every second ¹³⁴Cs⁺ ion flowing into the lateral space was pumped into the cells rather than proceeding, via the low resistance pathway, to the serosal bath. It is thus indicated that the paracellular convective flow of ¹³⁴Cs⁺ is driven by lateral Na⁺/K⁺-pumps. Transepithelial unidirectional ⁴²K⁺ fluxes did not reach steady state within an observation period of 70 min, indicating that components of the fluxes in both directions pass the large cellular pool of potassium ions. The ratio of unidirectional ²⁴Na⁺ fluxes was time-variant and declined from an initial value of 3.66 ± 0.34 to a significantly smaller steady-state value of 2.57 ± 0.26 (P < 0.001, N= 5 paired observations), indicating that sodium ions pass the epithelium both via the paracellular and the cellular pathway. Quantitatively, the larger ratio of paracellular Na⁺ fluxes, as compared to that of paracellular Cs⁺ fluxes, is compatible with convective flow of the two alkali metal ions through the same population of water-filled pores. With a new set of equations, the fraction of the sodium flux passing the basement membrane barrier of the lateral space that is recirculated through the cellular compartment is estimated. This fraction was, on average, 0.72 ± 0.03 (N= 5). It is concluded that isotonicity of the transportate can be maintained by producing a hypertonic fluid emerging from the lateral space combined with reuptake of salt via the cells. Received: 14 October 1998/Revised: 14 January 1999     

Passive sodium movements across the opercular epithelium: The paracellular shunt pathway and ionic conductance

Summary The unidirectional Na⁺, Cl^–, and urea fluxes across isolated opercular epithelia from seawater-adaptedFundulus heteroclitus were measured under different experimental conditions. The mean Na⁺, Cl^–, and urea permeabilities were 9.30×10^–6 cm·sec^–1, 1.24×10^–6 cm·sec^–1, and 5.05×10^–7 cm·sec^–1, respectively. The responses of the unidirectional Na⁺ fluxes and the Cl^– influx (mucosa to serosa) to voltage clamping were characteristic of passively moving ions traversing only one rate-limiting barrier. The Na⁺ conductance varied linearly with, and comprised a mean 54% of, the total tissue ionic conductance. The Cl^– influx and the urea fluxes were independent of the tissue conductance. Triaminopyrimidine (TAP) reduced the Na⁺ fluxes and tissue conductance over 70%, while having no effect on the Cl^– influx or urea fluxes. Mucosal Na⁺ substitution reduced the Na⁺ permeability 60% and the tissue conductance 76%, but had no effect on the Cl^– influx or the urea fluxes. Both the Na⁺ and Cl^– influxes were unaffected by respective serosal substitutions, indicating the lack of any Na⁺/Na⁺ and Cl^–/Cl^– exchange diffusion.The results suggest that the unidirectional Na⁺ fluxes are simple passive fluxes proceeding extracellularly (i.e., movement through a cation-selective paracellular shunt). This pathway is dependent on mucosal (external) Na⁺, independent of serosal (internal) Na⁺, and may be distinct from the transepithelial Cl^– and urea pathways.     

Li+ Pre‐Insertion Leads to Formation of Solid Electrolyte Interface on TiO2 Nanotubes That Enables High‐Performance Anodes for Sodium Ion Batteries

Recently, sodium ion batteries (SIBs) have been widely investigated as one of the most promising candidates for replacing lithium ion batteries (LIBs). For SIBs or LIBs, designing a stable and uniform solid electrolyte interphase (SEI) at the electrode–electrolyte interface is the key factor to provide high capacity, long‐term cycling, and high‐rate performance. In this paper, it is described how a remarkably enhanced SEI layer can be obtained on TiO₂ nanotube (TiO₂ NTs) arrays that allows for a strongly improved performance of sodium battery systems. Key is that a Li⁺ pre‐insertion in TiO₂ NTs can condition the SEI for Na⁺ replacement. SIBs constructed with Li‐pre‐inserted NTs deliver an exceptional Na⁺ cycling stability (e.g., 99.9 ± 0.1% capacity retention during 250 cycles at a current rate of 50 mA g^?1) and an excellent rate capability (e.g., 132 mA h g^?1 at a current rate of 1 A g^?1). The key factor in this outstanding performance is that Li‐pre‐insertion into TiO₂ NTs leads not only to an enhanced electronic conductivity in the tubes, but also expands the anatase lattice for facilitated subsequent Na⁺ cycling.     

Cation Metabolism in Relation to Cell Size in Synchronously Grown Tissue Culture Cell

In randomly grown tissue culture cells (mouse leukemic lymphoblast, L5178Y) the number, volume, and Na⁺ and K⁺ content increase as an exponential function with a doubling time of 11.3 hr. In synchronously grown cells the volume increase of the population and of single cells follows the same exponential function as in randomly grown cells. In contrast, the cation content fluctuates during a single cell cycle. About 1½ hr after the cell division burst (at the beginning of the S period), a net loss of K⁺ occurs for a period of about 1 hr amounting to about 20% of the total K. Over the next 5 to 6 hr, the deficit in K⁺ is eliminated. The Na⁺ content shows a double fluctuation. It falls during the cell division burst, rises when the K⁺ content decreases, falls again when K⁺ content rises, and then increases again before the next cell division burst. The net fluxes of both Na⁺ and K⁺ are very small compared to the unidirectional fluxes (less than 5%), thus small changes in the balance of influx and efflux account for the changes in cation content during the growth cycle. Both unidirectional fluxes increase dramatically (by a factor of two) about 2 hr after the cell division burst, and then remain constant until after the next cell division. The pattern of electrolyte regulation during cell division does not follow a simple function such as cell number, cell surface, or cell volume, but must be related to specific internal events in the cell.     

The effect of ethanol on ion transport in frog skin

Frog skin has been used as a model epithelial sodium-transporting system to study the effect of ethanol on ion transport. Treatment of the outside of frog skin with ethanol decreased the net sodium transport due to inhibition of ²²Na⁺ influx. Ethanol did not alter sodium outflux when bathing the outside of the skin. The inhibition was in proportion to the concentration of ethanol, 0.25 M resulting in 50% inhibition. The chloride permeability of the skin was increased several-fold when the skin was exposed to ethanol in either bathing solution. With 0.4 M ethanol in the inner bathing solution, all the unidirectional fluxes of Na⁺ and Cl^? were increased. The movement of Cl^? was evaluated by comparison of Cl^? flux with urea flux, since urea is thought to move passively across frog skin via an extracellular (shunt) pathway. Chloride flux was increased to a greater extent than urea flux. These experiments indicate that ethanol affects chloride permeability beyond an increase in extracellular ion flow and independent of its effect on Na⁺ transport.     

Dependence of water movement on sodium transport in kidney proximal tubule: A microperfusion study substituting lithium for sodium

Summary The relationship between water and sodium movements through the mammalian proximal convoluted tubule was investigated by substituting lithium for sodium. Proximal convoluted rat Kidney tubules were perfusedin vivo with a Ringer solution containing 107 meq/liter lithium and 42 meq/liter sodium. Several micropunctures were made along the same nephron, and [³H] inulin, [¹⁴C] glucose,²²Na, osmolality, Na, Mg and Cl were determined on each sample. Measurements of²²Na showed that sodium and lithium diffusion rates were practically identical throughout the entire epithelium. A one- for-one exchange of sodium for lithium induced a negative trans-epithelial net flux of Na from plasma to lumen. However, despite this negative flux, a positive net water movement was measured from lumen to plasma. This movement was proportional both to glucose reabsorption and to the rise in the chloride concentration, two mechanisms known to be dependent on the trans-cellular movement of sodium. It was therefore concluded that the net water flux was a function of the unidirectional transcellular net flux of Na.Rabbit proximal convoluted tubules were perfusedin vitro with a solution containing 75 meq/liter Li and 75 meq/liter Na on both the luminal and peritubular sides. Under these conditions, the water reabsorption rate dropped to half its control value. Water movement was therefore a function of the external sodium concentration, which in turn probably regulates the intracellular Na concentration.     

Low‐Cost Hollow Mesoporous Polymer Spheres and All‐Solid‐State Lithium,Sodium Batteries

A practical, low‐cost synthesis of hollow mesoporous organic polymer (HMOP) spheres is reported. The electrochemical properties of Li⁺/Na⁺‐electrolyte membranes with these spheres substituting for oxide filler particles in poly(ethylene oxide) (PEO)‐filler composite are explored. The electrolyte membranes are mechanically robust, thermally stable to over 250 °C, and block dendrites from a metallic‐lithium/sodium anode. The Li⁺/Na⁺ transfer impedance across the lithium/sodium–electrolyte interface is initially acceptable at 65 °C and scavenging of impurities by the porous‐spheres filler lowers this impedance relative to that with Al₂O₃. All‐solid‐state Li/LiFePO₄ and Na/NaTi₂(PO4)₃ cells give stable discharge capacity of ≈130 and 80 mAh g^?1, respectively, at 0.5 C and 65 °C for 100 cycles.     

Toward a Four‐Electron Redox Quinone Polymer for High Capacity Lithium Ion Storage

Despite recent advances, current polymeric organic cathode materials have failed to incorporate a high degree of lithium storage in a small molecular framework, resulting in low capacities relative to monomers. This report discloses the development of a lithium salt polymer of dihydroxyanthraquinone (LiDHAQS) capable of storing four Li⁺ per monomer. The combination of storing four Li⁺ per monomer and a low molecular weight monomer results in a capacity of 330 mA h g^?1, a record for this class of material. The additional redox events responsible for added Li⁺ storage occur between 3.0 and 3.6 V versus Li/Li⁺ resulting in an average discharge potential of 2.5 V versus Li/Li⁺. These metrics combined yield a high energy density of 825 W h kg^?1 which is a 55% improvement over commercial lithium cobalt oxide. The high performance of LiDHAQS makes it a promising material for next generation Li⁺ cathodes.     

The ionic relations of Porphyra purpurea(Roth) C.Ag. (Rhodophyta, Bangiales)

Abstract Radioisotope equilibration techniques have been used to determine the intracellular concentration of K⁺, Na⁺ and Cl_?, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of ⁴²K⁺, ²⁴Na⁺ and ³⁶C1^? are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K⁺ and Cl^? and against Na⁺. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K⁺ and Cl^? influx and Na⁺ efflux. ‘Active’ uptake and ‘passive’ loss of K⁺ and Cl^? are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K⁺ and Cl^? may be due to ‘exchange diffusion’ (K⁺/K⁺ and Cl^?/Cl^?antiport).     

Polysulfide‐Shuttle Control in Lithium‐Sulfur Batteries with a Chemically/Electrochemically Compatible NaSICON‐Type Solid Electrolyte

A NaSICON‐type Li⁺‐ion conductive membrane with a formula of Li_{1+ x} Y _x Zr_{2? x} (PO₄)₃ (LYZP) (x = 0–0.15) has been explored as a solid‐electrolyte/separator to suppress polysulfide‐crossover in lithium‐sulfur (Li‐S) batteries. The LYZP membrane with a reasonable Li⁺‐ion conductivity shows both favorable chemical compatibility with the lithium polysulfide species and exhibits good electrochemical stability under the operating conditions of the Li‐S batteries. Through an integration of the LYZP solid electrolyte with the liquid electrolyte, the hybrid Li‐S batteries show greatly enhanced cyclability in contrast to the conventional Li‐S batteries with the porous polymer (e.g., Celgard) separator. At a rate of C/5, the hybrid Li ||LYZP|| Li₂S₆ batteries developed in this study (with a Li‐metal anode, a liquid/LYZP hybrid electrolyte, and a dissolved lithium polysulfide cathode) delivers an initial discharge capacity of ≈1000 mA h g^?1 (based on the active sulfur material) and retains ≈90% of the initial capacity after 150 cycles with a low capacity fade‐rate of <0.07% per cycle.     

Ouabain switches Na+ transport to Na+/Na+ equivalent exchange in normal and apoptotic lymphoid cells

A theory of change of the ionic fluxes in the lymphoid cells in their transition from normal to apoptosis we have developed previously is applied to the analysis of Na⁺/Na⁺ exchange fluxes in human lymphoid cells U937 exposed to ouabain. We solve a system of equations describing changes in the intracellular concentrations of Na⁺, K⁺ and Cl^?, membrane potential and cell volume. It is shown that the Na⁺ influx (I _Na/Na) and output flux through the Na⁺/Na⁺ tract increased 4 times in 8 h after disconnecting Na⁺/K⁺-ATPase for normal cell U937. These fluxes increased 2.6 times for apoptotic cells. The value of I _Na/Na after 8 h off pump by ouabain is 97% of the total Na⁺ input for both cell types. It is concluded that ouabain not only inhibits the Na⁺/K⁺-ATPase, but also increases Na⁺ exchange fluxes through the Na⁺/Na⁺ tract, thereby switching sodium transport across the membrane of lymphoid cells to Na⁺/Na⁺ equivalent exchange.     

Short circuit current in tight and leaky epithelia

The effect of short circuit current on the unidirectional fluxes of ions transported across tight and leaky epithelia was investigated. It was found that short circuiting of the frog gastric mucosa (classified as a tight epithelium) caused a decrease of the passive J_ms^C1 and a significant increase of the net Cl^? secretion. However, no significant change of H⁺ secretory rate was observed. On the other hand, short circuiting of the mouse intestine (a known leaky membrane) caused a simultaneous increase of both J_ms and J_sm fluxes of Na⁺ while the net fluxes of Na⁺ and Cl^? remained unchanged. Also, short circuiting did not change the water permeability of the mouse intestine. To explain some of these results a theoretical model is presented to demonstrate that while short circuiting can block the passive ionic movement, it will cause an increase in the energy consumption of the system and introduce certain important changes in the ionic barriers and e.m.fs. The simultaneous increase in the unidirectional fluxes of Na⁺ under short circuit conditions can best be explained by a decrease in the polarized nature of the transepithelial shunt, thereby increasing the diffusion coefficient of the ion(s). Such an increase is specially favorable to the Na⁺ rather than an anion.     

Unidirectional Na(+) and Ca (2+) fluxes in two euryhaline teleost fishes, Fundulus heteroclitus and Oncorhynchus mykiss, acutely submitted to a progressive salinity increase

Na⁺ and Ca²⁺ regulation were compared in two euryhaline species, killifish (normally estuarine-resident) and rainbow trout (normally freshwater-resident) during an incremental salinity increase. Whole-body unidirectional fluxes of Na⁺ and Ca²⁺, whole body Na⁺ and Ca²⁺, and plasma concentrations (trout only), were measured over 1-h periods throughout a total 6-h protocol of increasing salinity meant to simulate a natural tidal flow. Killifish exhibited significant increases in both Na⁺ influx and efflux rates, with efflux slightly lagging behind efflux up to 60% SW, but net Na⁺ balance was restored by the time killifish reached 100% SW. Whole body Na⁺ did not change, in agreement with the capacity of this species to tolerate daily salinity fluctuations in its natural habitat. In contrast, rainbow trout experienced a dramatic increase in Na⁺ influx (50-fold relative to FW values), but not Na⁺ efflux between 40 and 60% SW, resulting in a large net loading of Na⁺ at higher salinities (60–100% SW), and increases in plasma Na⁺ and whole body Na⁺ at 100% SW. Killifish were in negative Ca²⁺ balance at all salinities, whereas trout were in positive Ca²⁺ balance throughout. Ca²⁺ influx rate increased two- to threefold in killifish at 80 and 100% SW, but there were no concomitant changes in Ca²⁺ efflux. Ca²⁺ flux rates were affected to a larger degree in trout, with twofold increases in Ca²⁺ influx at 40% SW and sevenfold increases at 100% SW. Again, there was no change in Ca²⁺ efflux with salinity, so plasma Ca²⁺ concentration increased in 100% SW. As the killifish is regularly submitted to increased salinity in its natural environment, it is able to rapidly activate changes in unidirectional fluxes in order to ensure ionic homeostasis, in contrast to the trout.     

Coordinating Anions “to the Rescue” of the Lithium Ion Mobility in Ternary Solid Polymer Electrolytes Plasticized With Ionic Liquids

Lithium salts with low coordinating anions such as bis(trifluoromethanesulfonyl)imide (TFSI) have been the state-of-the-art for polyethylene oxide (PEO)-based “dry” polymer electrolytes for 3 decades. Plasticizing PEO with TFSI-based ionic liquids (ILs) to form ternary solid polymer electrolytes (TSPEs) increases conductivity and Li⁺ diffusivity. However, the Li⁺ transport mechanism is unaffected compared to their “dry” counterparts and is essentially coupled to the dynamics of the polymer host matrix, which limits Li⁺ transport improvement. Thus, a paradigm shift is hereby suggested: the utilization of more coordinating anions such as trifluoromethanesulfonyl-N-cyanoamide (TFSAM), able to compete with PEO for Li⁺ solvation, to accelerate the Li⁺ transport and reach a higher Li⁺ transference number. The Li–TFSAM interaction in binary and ternary TFSAM-based electrolytes is probed by experimental methods and discussed in the context of recent computational results. In PEO-based TSPEs, TFSAM drastically accelerates the Li⁺ transport (increases Li⁺ transference number by a factor 6 and the Li⁺ conductivity by 2–3) and computer simulations reveal that lithium dynamics are effectively re-coupled from polymer to anion dynamics. Last, this concept of coordinating anions in TSPEs is successfully applied in LFP||Li metal cells leading to enhanced capacity retention (86% after 300 cycles) and an improved rate performance at 2C.     

Recent Developments of the Lithium Metal Anode for Rechargeable Non‐Aqueous Batteries

Over the last 40 years, metallic lithium as an anode material has been of great interest owing to its high energy density. However, dendritic lithium growth causes serious safety issues. Awareness and understanding of the Li deposition and stripping processes have grown rapidly especially in recent years, and consequently, there have been many attempts to suppress the Li dendrites. Recent developments that have modified the electrolytes and the Li anode in order to inhibit the growth of Li dendrite and improve cycling performance are summarized. It has been shown that current density, solid‐electrolyte interphase (SEI) film, Li⁺ transference number, and shear modulus have significant impact on the growth behavior and the Coulombic efficiency. Various methods have been introduced to increase the surface area of the Li anode, enhance Li⁺ conductivity, form stable SEI film, and improve mechanical strength of electrolytes. These approaches are discussed in details, and the perspectives regarding the future use of Li anode are also outlined. It is hoped that this review will facilitate the future development of Li metal batteries.     

Single-file diffusion through K+ channels in frog skin epithelium

Summary The ratio between the unidirectional fluxes of K⁺ across the frog skin with K-permeable outer membranes was determined in the absence of Na⁺ in the apical solutions. The experiments were performed under presteady-state conditions to be able to separate the flux ratio for K⁺ through the cells from contributions to the fluxes through extracellular leaks. The cellular flux ratio deviated strongly from the value calculated from the flux ratio for electrodiffusion. The experiments can be explained if the passive K transport through the epithelial cells proceeds through specific channels by single-file diffusion with a flux ratio exponent of about 2.5.     

Cation flux in the ehrlich ascites tumor cell evidence for Na-for-Na and K-for-K exchange diffusion

In a previous study, evidence was presented for an external Na⁺-dependent, ouabain-insensitive component of Na⁺ efflux and an external K⁺-dependent component of K⁺ efflux in the Ehrlich ascites tumor cell. Evidence is now presented that these components are inhibited by the diuretic furosemide and that under conditions of normal extracellular Na⁺ and K⁺ they represent Na⁺-for-Na⁺ and K-⁺for-K⁺ exchange mechanisms. Using ⁸⁶Rb to monitor K⁺ movements, furosemide is shown to inhibit an ouabain-insensitive component of Rb⁺ influx and a component of Rb⁺ efflux, both representing approx. 30% of the total fux. Inhibition of Rb⁺ efflux is greatly reduced by removal of extracellular K⁺. Furosemide does not alter steady-state levels of intracellular K⁺ and it does not prevent cells depleted of K⁺ by incubation in the cold from regaining K⁺ upon warming. Using ²²Na to monitor Na⁺ movements, furosemide is shown to inhibit an ouabain-insensitive component of unidirectional Na⁺ efflux which represents approx. 22% of total Na⁺ efflux. Furosemide does not alter steady-state levels of intracellular Na⁺ and does not prevent removal of intracellular Na⁺ upon warming from cells loaded with Na⁺ by preincubation in the cold. The ability of furosemide to affect unidirectional Na⁺ and K⁺ fluxes but not net fluxes is consistent with the conclusion that these components of cation movement across the cell membrane represent one-for-one exchange mechanisms. Data are also presented which demonstrate that the uptake of α-aminoisobutyrate is not affected by furosemide. This indicates that these components of cation flux are not directly involved in the Na⁺-dependent amino acid transport system A.     

Enhanced Stability of Li Metal Anodes by Synergetic Control of Nucleation and the Solid Electrolyte Interphase

Use of a protective coating on a lithium metal anode (LMA) is an effective approach to enhance its coulombic efficiency and cycling stability. Here, a facile approach to produce uniform silver nanoparticle‐decorated LMA for high‐performance Li metal batteries (LMBs) is reported. This effective treatment can lead to well‐controlled nucleation and the formation of a stable solid electrolyte interphase (SEI). Ag nanoparticles embedded in the surface of Li anodes induce uniform Li plating/stripping morphologies with reduced overpotential. More importantly, cross‐linked lithium fluoride‐rich interphase formed during Ag⁺ reduction enables a highly stable SEI layer. Based on the Ag‐LiF decorated anodes, LMBs with LiNi_1/3Mn_1/3Co_1/3O₂ cathode (≈1.8 mAh cm^?2) can retain >80% capacity over 500 cycles. The similar approach can also be used to treat sodium metal anodes. Excellent stability (80% capacity retention in 10 000 cycles) is obtained for a Na||Na₃V₂(PO₄)₃ full cell using a Na‐Ag‐NaF/Na anode cycled in carbonate electrolyte. These results clearly indicate that synergetic control of the nucleation and SEI is an efficient approach to stabilize rechargeable metal batteries.     

Compartmental analysis of 6Li/7Li isotope exchange in equilibrium conditions in mouse plasma

The compartmental analysis of lithium in the mouse plasma has been performed using the stable isotopes, 6Li and 7Li, as tracers. The animals were kept under stationary conditions (concentration of total lithium in plasma maintained equal to 0.28 mM) during the experiment. The isotopic exchange, 6Li/7Li, was described to a good approximation by combining two first-order processes (characteristic parameters: 89 microM and 2.071 X 10(-3) X min-1 for the first one, and 193 microM and 2.215 X 10(-4) X min-1 for the second one). From these kinetic data, it was estimated that the lithium capacities of the plasma and of the cells were 282 and 454 nmol X ml-1, and that the unidirectional fluxes of lithium between plasma and cells and through the kidneys were 0.259 and 0.227 nmol X ml-1 X mn-1. Since the method makes use only of stable, hence harmless, isotopes, one might think of extending it to direct experimentation in man.