Sodium Translocation Research Articles

Na+-K+2Cl-Cotransport in the Thick Ascending Limb of Henle

The operation of this recently recognized cotransport unit, which tightly couples the translocation of sodium, potassium, and chloride across cell membranes of the thick ascending limb of Henle's loop, is described, along with the pathologic derangements of renal function that give these physiologic phenomena their clinical correlation.

Discrimination between transmembrane ion gradient-driven and electron transfer-driven ATP synthesis in the methanogenic bacteria

As with Methanococcus voltae [(1986) FEBS Lett. 200, 177–180], ATP synthesis in Methanobacterium thermoautotrophicum (ΔH) can be driven by the imposition of a sodium gradient, but only in the presence of a counterion. Monensin (but not SF6847) inhibits this synthesis. Methanogenic electron transfer-driven ATP synthesis, however, is insensitive to the combination of these two ionophores. In M. voltae, 117 μM diethylstilbestrol effectively inhibits both membrane potential- and sodium gradient-driven ATP synthesis, but has no effect on ATP production coupled to methanogenesis. In Mb. thermoautotrophicum (ΔH), a similar pattern of inhibition is exhibited by harmaline, an inhibitor of sodium-linked membrane transport systems. We conclude that ATP-driven sodium translocation and electron transfer-driven ATP synthesis are accomplished by separate entities, at least for these two only distantly related species of methanogen.

An NADH:Quinone oxidoreductase of the halotolerant bacterium Ba 1 is specifically dependent on sodium ions

The rate of NADH oxidation by inverted membrane vesicles prepared from the halotolerant bacterium Ba 1 of the Dead Sea is increased specifically by sodium ions, as observed earlier in whole cells. The site of this sodium effect is identified as the NADH: quinone oxidoreductase, similarly to the other such system known, Vibrio alginolyticus ( H. Tokuda and T. Unemoto (1984) J. Biol. Chem. 259, 7785–7790 ). Sodium accelerates quinone reduction severalfold, but oxidation of the quinol, with oxygen as terminal electron acceptor, is unaffected. The sodium-dependent pathway of quinone reduction exhibits higher apparent affinity to extraneous quinone (Q-2) than the sodium-insensitive pathway, and is specifically inhibited by 2-heptyl-4-hydroxyquinoline N-oxide. ESR spectra of the membranes contain a feature at g = 1.98 which is tentatively identified as one originating from semiquinone. This feature is increased by NADH and decreased by addition of Na +, suggesting that, as proposed from different kinds of evidence for the V. alginolyticus system, sodium affects the semiquinone reduction step. As in the other system, the site of sodium stimulation in Ba 1 probably corresponds to the site of sodium translocation, which was shown earlier ( S. Ken-Dror, R. Shnaiderman, and Y. Avi-Dor (1984) Arch. Biochem. Biophys. 229, 640–649 ) to be linked directly to a redox reaction in the respiratory chain.

39] Sodium translocation by NADH oxidase of Vibrio alginolyticus: Isolation and characterization of the sodium pump-defective mutants

Publisher Summary The marine bacterium Vibrio alginolyticus possesses a primary electrogenic Na + extrusion system (a Na + pump) which is coupled to respiration. From the isolation of the Na + pump-defective mutants, it became clear that the Na + pump is coupled to NADH oxidase which requires Na + for maximum activity and is highly sensitive to 2-heptyl-4-hydroxyquinoline N -oxide (HQNO), a specific inhibitor of the Na + pump. It is recently shown that the reduced nicotinamide adenine dinucleotide (NADH) oxidase reconstituted into liposomes functions as the Na + pump. The Na + pump generates an electrochemical potential of Na+ (a Na + motive force), which is an immediate driving force for various substrate transport systems and flagella motility. As the activity of the Na + pump is maximum at pH about 8.5, and minimum at pH 6.0, generation of the Na + motive force shows striking difference in the sensitivity to a proton conductor, carbonyl cyanide m-chlorophenylhydrazone (CCCP), depending on external pH. At acidic pH, respiratory chain extrudes only H + leading to the generation of the protonmotive force (Δp). Thus, collapse of Δp by CCCP concomitantly inhibits the generation of the Na + motive force. The generation of Δψ in the presence of CCCP leads to the intracellular accumulation of H + until a steady state is reached. Therefore, the Na + pump activities in whole cells can be examined from CCCP-resistant Na+ extrusion, CCCP-resistant Δψ generation, and CCCP-dependent H+ accumulation. In this chapter, examinations of the Na + pump activity in whole cells and membranes are described.

Relations entre la tolérance ou la sensibilité à la salinité lors de la germination des semences et les composantes de la nutrition en sodium

Adsorption, absorption and translocation of sodium were compared in three species showing an ascending degree in tolerance to salinity: red cabbage (tolerant) shows higher Root Cationic Exchange Capacity than tomato (sensitive) or radish (intermediate). At low NaCl concentrations, tomato accumulates the greatest quantities of sodium; but Na+ translocation remains proportional to the quantity absorbed in the three plants. At high salt concentrations, diffusive phenomena explain similar accumulation in every plant, but red cabbage quickly localises 50% of Na+ amount in cotyledons, while this element stays stored in tomato roots. The consequence of these three nutrition phases was discussed in relation to the behaviour observed at the germination time of these same plants.

Calcium transport by a β-diketone in model membranes

The β-diketone 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione (FOD) translocates calcium from an aqueous medium into an organic phase. FOD is less efficient than but acts synergistically with A23187 in causing calcium translocation. The FOD-mediated process of calcium translocation is inhibited by NaCl, although the translocation of sodium by FOD is two to three orders of magnitude lower than that of calcium, when expressed relative to the concentration of these cations in the aqueous medium. At pH 7.4, FOD mediates calcium exchange-diffusion in fluid liposomes as efficiently as A23187. The extent of exchange-diffusion depends on the rigidity and cholesterol content of the liposomes. Conformational analysis of the complex formed by two molecules of FOD and one calcium atom at a simulated membrane interface reveals the existence of several interconvertible, asymmetrical and more-or-less planar configurations. The efficiency of FOD-mediated calcium ionophoresis thus appears to be regulated in a multifactorial manner by such factors as the concentration of calcium and monovalent cations, chemical composition and fluidity of the membrane, availability of other ionophoretic molecules and spatial configuration of the calcium complex.

Binding order of substrates to the sodium and potassium ion coupled L-glutamic acid transporter from rat brain.

Efflux of L-glutamic acid from synaptic plasma membrane vesicles requires external potassium. This requirement is saturated by concentrations of about 15 mequiv/L potassium. In the absence of potassium, L-glutamic acid can be released from the vesicles in the presence of external L-glutamic acid. This stimulation does not require external sodium but is dependent on the external concentration of L-glutamic acid. Half-maximal effects are obtained by concentrations of about 1 microM which are very similar to the apparent Km for L-glutamic acid influx. Efflux of labeled glutamate driven by external sodium plus glutamate requires internal sodium. These findings suggest that the transporter displays an asymmetric behavior toward sodium. This ion dissociates much more slowly than L-glutamic acid on the external surface of the membrane but not on the internal surface. Furthermore, it appears that the transporter translocates potassium in a step distinct from the L-glutamic acid translocation step. The simplest explanation is that upon translocation of sodium and L-glutamic acid and their release to the inside, potassium binds to the transporter, enabling it to return to the outside to allow initiation of a new transport cycle.

Inhibition by sodium of A23187-mediated calcium translocation

Sodium inhibits in a dose-related fashion the translocation of calcium from an aqueous milieu into an organic phase containing the divalent-cation ionophore A23187. This inhibitory effect is reproduced by other monovalent cations, modulated by the nature of the anion in the sodium halide, and inversely related to the absolute amount of calcium translocated. The inhibitory effect cannot be attributed to a change in osmolarity or ionic strength, to sequestration of the ionophoretic molecule at the interface between the aqueous and organic phases, or to translocation of sodium or chloride. These findings indicate that sodium may directly affect the handling of calcium by ionophoretic systems specifically mediating the transport of divalent cations.

SODIUM NUTRITION OF PASTURE PLANTS I. TRANSLOCATIGN OF SODIUM AND POTASSIUM IN RELATION TO TRANSPIRATION RATES

ABSTRACTA study of transpiration rates, and of uptake and translocation of sodium and potassium, has supported a previous classification made for certain pasture and fodder species. The plants termed natrophiles were found to have relatively high transpiration rates and to translocate relatively large amounts of absorbed sodium from root systems into leaves. Plants termed natrophobes had lower transpiration rates and translocated less sodium from roots to leaves. In contrast, potassium was readily translocated by both natrophiles and natrophobes; consequently, compared with natrophobes, natrophiles had low K/Na ratios in their leaves. In general, transpiration rate was less associated with absorption of sodium by roots than with translocation of sodium from roots to aerial parts. The practical and ecological implications of these results are discussed.

SODIUM NUTRITION OF PASTURE PLANTS II. EFFECT OF SODIUM CHLORIDE ON GROWTH, CHEMICAL COMPOSITION AND THE REDUCTION OF NITRATE NITROGEN

ABSTRACTThe effect of increasing concentrations of sodium chloride in the root zone on growth, chemical composition and nitrate reductase activity of perennial ryegrass and timothy was investigated in a glasshouse pot experiment. For ryegrass, a natrophile, sodium chloride had little effect on growth, whereas for timothy, a natrophobe, growth was severely depressed by comparatively low concentrations of salt. The result also indicate that translocation of sodium into the leaves of timothy took place readily only after the accumulation sites in the roots and lower stems had been saturated with this element. This means that relatively large quantities of sodium chloride were needed to produce concentrations of sodium in the leaves of timothy as high as those normally found in the leaves of ryegrass. Sodium chloride increased the uptake of total and nitrate‐nitrogen but, in contrast, depressed the uptake of potassium by ryegrass and timothy It was therefore concluded that the marked stimulation by sodium chloride of nitrate reductase activity in both species was more the result of the increased uptake of nitrates than a specific effect of this salt on the enzyme. The practical implications of these results are discussed.

Ionophore-mediated cation translocation in artificial systems: II. — X537A-mediated calcium and sodium translocation

The ionophore X537A translocates both calcium and sodium from an aqueous into an organic solution. At non saturating cationic concentrations, each atom of calcium seems to react with two molecules of ionophore, whereas each atom of sodium apparently reacts with only one molecule of X537A. The phenomena of sodium and calcium translocation, respectively, are competitive and are both inhibited when the pH of the aqueous phase is decreased.

Spectrophotometric identification of the pigment associated with light-driven primary sodium translocation in Halobacterium halobium.

Spectrophotometric identification of the pigment associated with light-driven primary sodium translocation in Halobacterium halobium.

Light-driven primary sodium ion transport in Halobacterium halobium membranes.

Light-induced sodium extrusion from H halobium cell envelope vesicles proceeds largely through an uncoupler-sensitive pathway involving bacteriorhodopsin and a proton/sodium antiporter. Vesicles from bacteriorhodopsin-negative strains also extrude sodium ions during illumination, but this transport is not sensitive to uncouplers and has been proposed to involve a light-energized primary sodium pump. Proton uptake in such vesicles is passive, and under steady-state illumination the large electrical potential (negative inside) is just balanced by a pH difference (acid inside), so that the proton-motive force is near zero. Action spectra indicated that this effect of illumination is attributable to a pigment absorbing near 585 nm (cf 568 for bacteriorhodopsin). Bleaching of the vesicles by prolonged illumination with hydroxylamine results in inactivation of the transport; retinal addition causes partial return of the activity. Retinal addition also causes the appearance of an absorption peak at 588 nm, while the absorption of free retinal decreases. The 588 nm pigment is present in very small quantities (0.13 nmole/mg protein), and behaves differently from bacteriorhodopsin in a number of respects. Vesicles can be prepared from bacteriorhodopsin-containing H halobium strains in which primary transport for both protons and sodium can be observed. Both pumps appear to cause the outward transport of the cations. The observations indicated the existence of a second retinal protein, addition to bacteriorhodopsin, in H halobium, which is associated with primary sodium translocation. The initial proton uptake normally observed during illumination of whole H halobium cells may therefore be a passive flux in response to the primary sodium extrusion.

Synergistic effects of hypoglycaemic sulphonylureas and antibiotic ionophores upon calcium translocation.

1 Hypoglycaemic sulphonylureas, such as tolbutamide and gliclazide, provoke the translocation of calcium from an aqueous medium into or across a hydrophobic region. The combined effect of sulphonylureas and antibiotic ionophores upon such a process was investigated. 2 The magnitude of the sulphonylurea-induced translocation of calcium was more marked in the presence than in the absence of A23187. Gliclazide and tolbutamide also enhanced, although less markedly, X537A-mediated calcium translocation. The effect of the sulphonylureas was even less marked in the presence of both ionophores, which acted synergistically in causing calcium translocation. 3 A non-hypoglycaemic sulphonylurea and diazoxide failed to affect ionophore-mediated calcium translocation. Gliclazide failed to enhance X537A-mediated sodium translocation. 4 It is proposed that the primary site of action of hypoglycaemic sulphonylureas upon calcium-dependent physiological processes may correspond to a drug-induced facilitation of calcium transport across the plasma membrane, as mediated by native ionophores.

Salinity Damage to Norfolk Island Pines Caused by Surfactants. I. The Nature of the Problem and Effect of Potassium, Sodium and Chloride Concentration on Uptake by Roots

As part of an investigation into the deterioration of Norfolk Island pine, Araucaria heterophylla (Salisb.) Franco, on the coast of eastern Australia, seedlings were grown in nutrient solutions in which sodium was substituted for potassium over the range 0.1 - 2.1 mM to give six treatments, each with four ratios of sulfate to chloride. Potassium was freely taken up and translocated to the shoots, the levels in the shoots being higher than those in the roots. However, the levels of potassium in both shoots and roots were significantly reduced in solutions in which sulfate predominated over chloride. Uptake and translocation of sodium was restricted, the ratio of sodium (shoots) to sodium (roots) being less than unity. The concentration of chloride in the shoots and roots generally increased with increasing solution chloride concentration but was significantly reduced at the lowest potassium-to-sodium ratio. In a second experiment the ratio of sodium to potassium was kept at 50:1, sodium and chloride in the solutions increasing from 2.5 to 460 mM and potassium from 0.05 to 9.2 mM. At the lower concentrations, uptake and translocation followed similar patterns to those found in the first experiment. However at solution concentrations of 20 mM sodium and above, levels of sodium in the shoots exceeded those of potassium and chloride. At sodium chloride concentrations of 260mM - 460mM, plants showed toxic symptoms with salt encrustations appearing on the stems. Analysis of the saturation extracts of soils taken from beneath affected seaside trees showed that the concentrations of sodium and chloride were not sufficiently high to account for the high levels of these elements found in the shoots of affected trees.

Sodium and chloride fluxes in synaptosomes in vitro.

Abstract—Synaptosomes incubated in a physiological saline extrude sodium and take up potassium. As would be expected this process is completely blocked by metabolic inhibitors such as cyanide and iodoacetate. However, when metabolic inhibitors are replaced by ouabain (100 μM) there is an increase in the steady state intrasynaptosomal sodium and chloride content even though there is no change in the potassium content. The increases are prevented when synaptosomes are incubated with metabolic inhibitors in addition to ouabain. There is therefore a ouabain‐insensitive process that transports sodium, chloride and concomitantly water into synaptosomes. It appears not to function when the supply of metabolic energy is inhibited. The diuretic furosemide (1 mM) in the presence of ouabain inhibits the entry of sodium and chloride without affecting the intrasynaptosomal potassium concentration. Ethacrynic acid (1 mM) has a somewhat similar effect but in addition appears to damage the synaptosome membrane.Kinetic measurements were made of the uptake of sodium, potassium and chloride under conditions of metabolic inhibition and the permeability constants of the membrane determined. Values of 0.068, 0.117 and 0.032 × 10‐6 (cm s‐1) were found for the permeability constants of the membrane to (respectively) sodium, potassium and chloride. Measurements of the rate of uptake in the presence of ouabain revealed an inwardly directed sodium and chloride flux of 5‐20 pmol cm‐2 s‐1. Calculation of the fluxes from the steady state ion concentrations also reveals an inwardly directed sodium and chloride flux, though of lesser magnitude. The influx of water is less than would be expected to preserve osmotic equality suggesting that the translocation of sodium and chloride is the primary event. Although its function remains uncertain the flux has a considerable effect on the ion content of synaptosomes.

Effect of some soil amendments on sodium uptake and translocation in dry beans (P. vulgaris L.) in relation to sodium toxicity

SUMMARYBean plants (Phaseolus vulgaris L.) were grown in field plots with the objective of comparing the effect of some soil amendments on sodium uptake and translocation at three levels of salinity in the soil.Gypsum and wheat straw mulch treatments reduced the translocation of sodium from the roots to the stems and leaves at the higher external sodium level. Incorporation of animal manure with the soil had little effect on translocation at the higher level but may have promoted sodium translocation to the stems at the lower level.Plant growth and survival were negatively correlated with the sodium content in the plant, particularly with that of the stems.

Diphenylhydantoin and potassium transport in isolated nerve terminals.

THE ANTIEPILEPTIC ACTION OF DIPHENYLHYDANTOIN (DPH) HAS BEEN EXPLAINED BY TWO DIFFERENT THEORIES: (a) that DPH stimulates the Na-K pump; (b) that DPH specifically blocks the passive translocation of sodium. Since electrophysiological experiments have recently suggested abnormal synaptic mechanisms as the basis for epileptogenic discharges, the action of DPH on K transport within synaptic terminals isolated from "normal" rat brain cortex was examined directly. A rapid filtration technique was used to assess in vitro potassium transport within synaptosomes. In vivo DPH did not significantly change endogenous K content within synaptosomes. With sodium (50 mM) and potassium (10 mM) concentrations optimal for Na-K pump activity, in vivo and in vitro DPH (10(-4) M) had minimal or no effects on total K uptake. DPH stimulated potassium uptake within synaptosomes under two situations: (a) at high sodium (50-100 mM) and low potassium (less than 2 mM) concentrations; (b) when synaptosomes were incubated with ouabain (10(-4) M) 50 mM Na and 10 mM K. In both situations, K was leaking out of synaptic terminals and the enhancement in net K uptake roughly corresponded to the ouabain inhibitable segment. In the absence of ouabain, the stimulatory effects of DPH were not observed when K was 2 mM or higher and when Na was 10 mM or lower. The stimulatory effects of in vitro DPH appeared over a range of concentrations from 10(-4) to 10(-10) M while single intraperitoneal injections of DPH had to be administered for 2 days before its effects were observed on synaptosomal K transport. The present data provided direct evidence for DPH stimulation of active potassium transport within synaptosomes under ionic conditions simulating the depolarized state. At other ionic conditions, DPH had inhibitory or no effects on K uptake. Although the results do not specify whether the effects of DPH on the Na-K pump are direct or indirect, they suggest that the action of DPH depends upon the state of the membrane and the specific ionic environment.

The Mechanism of Action of Digitalis

The ability of digitalis to potentiate cardiac contraction is intimately related to its interference with the active transport mechanism involved in the translocation of sodium and potassium across the cell membrane. This is also the mechanism that explains the toxicity problems so often encountered with use of the cardiac glycosides—myocardial irritability and heart block.

The absorption and translocation of sodium by maize seedlings

The absorption and subsequent distribution of sodium and potassium has been examined in maize seedlings in short-term experiments using sodium-22 and potassium-42. The absorption and translocation of sodium by different segments of intact seedlings was also investigated. Although absorption of potassium exceeded that of sodium by a factor of about 50, there was no evidence that the entry of sodium was confined to a small region of the root. Determinations of the relative quantities of sodium and potassium in the xylem exudate of detached roots showed that the ratio of sodium to potassium decreased with increasing length of the root. These results suggested that upward movement of sodium in the xylem vessels was progressively reduced towards the basal part of the root. This conclusion was supported by microautoradiographs, which showed that although the concentration of sodium within the endodermis was greater than that in the cortex, there was an apparent decrease in the sodium content of the major xylem vessels at the basal end of the root.