Replacement Of Sodium Ions Research Articles

Uptake of sulfobromophthalein-glutathione conjugate by isolated hepatocytes.

Uptake of sulfobromophthalein-glutathione conjugate (BSP-GS) was studied using isolated hepatocytes and was compared with previous results with the parent BSP (Schwenk et al., Eur. J. Biochem. 64: 189-197, 1976). Adsorption of BSP-GS to the liver cell membrane has two sites with different affinities and binding capacities. Uptake of the conjugate is decreased by two metabolic inhibitors and appears to be saturable up to 12.5 microM with an apparent Km of 4 microM (7 for BSP) and a Vmax of 0.16 nmol x mg protein-1 x min-1 (2.6 for BSP). Similar to the parent BSP at higher concentrations a second mechanism of uptake is observed indicated by the nonlinear Hanes plot. SP-GS transport is competitively inhibited by BSP with a Ki of about 1 microM, and, similar to BSP, replacement of sodium ions in the medium had little effect on the rates of uptake. These results suggest a common transport mechanism for BSP and its glutathione conjugate. Furthermore, the effect of organic anions, bases, and steroids on uptake of BSP-GS has been tested.

Uptake of unconjugated bilirubin by isolated rat hepatocytes

The mechanism responsible for the hepatic uptake of unconjugated bilirubin was examined in isolated rat hepatocytes from control and phenobartital-pretreated rats. The uptake was extremely rapid and the equilibrium between cell and medium was attained within 60 s with a 100-fold higher concentration in the cell than the medium. The initial velocity of uptake (Vo) exhibited a linear relationship to the bilirubin concentration in the medium. Pretreatment of cells with various metabolic inhibitors had no effect on the uptake of unconjugated bilirubin. Ouabain did significantly decrease Vo, but replacement of sodium ion with choline or lithium had no effect on bilirubin uptake. The organic acids sulfobromophthalein (112 muM) and taurocholic acid (50 (muM) and two steroidal compounds, diethylstilbestrol (50 muM) and spironolactone (50 muM), had no effect on the uptake of bilirubin. It is suggested that bilirubin gains access to the hepatocyte interior by passive diffusion into and through the lipid membrane and that intracellular binding may explain the high degree of bilirubin accumulation associated with the isolated hepatocytes.

Investigations of the ionic mechanisms of bursting activity in Helix pomatia neurons

Steady-state current-voltage characteristics of the membrane and ionic currents arising during changes in membrane potential in bursting neurons ofHelix pomatia were studied by the voltage clamp method. The steady-state current-voltage characteristics of the membrane were shown to have a nonlinear region. Replacement of sodium ions by Tris-HC1 ions in the external solution completely abolishes this nonlinearity. Hyperpolarization of the membrane under voltage clamp conditions leads to the development of an outward current which reaches a maximum and then is inactivated. This current has a reversal potential in the region of the potassium equilibrium potential. Depolarization of the membrane to the threshold value for excitation of uncontrollable regions of the axon hillock causes the appearance of a slow inward current. After reaching a maximum, the inward current falls to zero. A model of generation of waves in a bursting neuron is suggested.

Role of active ion transport in reception of the generator potential of the isolated frog muscle spindle

The effect of complete replacement of sodium ions by lithium ions in Ringer's solution and of 10−4 M ouabain on the receptor potential of the isolated frog muscle spindle was investigated. Initially, under the influence of lithium ions and ouabain, the hyperpolarization phase of this potential diminished and disappeared, and later the same fate befell the static and dynamic part of its depolarization phase. The rise time of the receptor potential was increased in a solution containing lithium ions but in the solution with ouabain it remained the same as initially. No appreciable changes were found in the rate of fall of the dynamic part of the depolarization phase. On rinsing the muscle spindle in normal Ringer's solution in the experiment with lithium ions recovery was incomplete, and in the experiments with ouabain the receptor responses were not restored.

The effect of lithium chloride on morphine- and pyrogen-induced hyperthermia in rats.

In rats, doses of morphine between 2.5 and 20 mg/kg produced hyperthermia, 50-400 mg/kg lithium chloride induced dose-dependent hypothermia. These doses of lithium chloride inhibited morphine- and pyrogen-induced hyperthermia. The hypothermic effect of lithium may be due to the replacement of sodium ions by lithium ions in the hypothalamus. The antagonism between morphine and lithium is nonspecific.

Potassium-induced motion increase in a central nervous ganglion.

1. By means of light-beating spectroscopy, a four-fold increase in the modulation of laser light scattered at right angles by a locust (Schistocerca gregaria, Forskål) ganglion is detected when potassium ions replace sodium ions in the Ringer solution. 2. This is interpreted as an increased level of motion of the scattering particles (size 0.3-3.0 mum, if viscosity is taken to be 0.01 poises). 3. The amplitude of the potassium-response is similar at all frequencies in the range 6.3-150 Hz and is reversible on return to normal (Na+) Ringer. 4. Desheathing the ganglion reduces the half-time of the potassium-response by 3-4 times. 5. By means of photon-correlation spectroscopy it was estimated that less than 10% of the tissue contributes to the motion detected. 6. Cyanide (1-2 mM) typically enhances the potassium-response and renders it irreversible, suggesting that the response is thermally rather than metabolically-driven. In addition, the dependence of both the correlation function and the power spectrum on the scattering angle is in the direction predicted for a diffusive process. 7. Cobaltous ions (2-10 mM), which block calcium entry into nerve cells, depress the potassium-response. 8. It is proposed that potassium-depolarization and the resultant calcium entry into the cells causes a partial liquefaction of the cytoplasms which is detected as an increase in the level of Brownian motion. This mechanism could be used in vesicular release or in growth.

FACTORS INFLUENCING THE EFFLUX OF [3H]GAMMAAMINOBUTYRIC ACID FROM SATELLITE GLIAL CELLS IN RAT SENSORY GANGLIA

Abstract—The spontaneous efflux of [3H]GABA from the satellite glial cells of rat dorsal root ganglia and the efflux evoked by 64 mM‐K+ were studied in the presence of 10‐5M‐amino‐oxyacetic acid and found not to be affected by 10‐4M‐D 600 or by elevated (9.6mM) Ca2+ in the absence of Mg2+. [3H]GABA efflux was increased by replacing sodium ions in the washing medium by choline ions and 64 mM‐K+ failed to increase the efflux further. The drugs veratridine (10‐6 and 10‐4M) and batrachotoxin (10‐8 and 10‐6 M) failed to alter the spontaneous efflux of [3H]GABA from the glial cells.A variety of compounds, including amino acids, a GABA analogue and a GABA antagonist were tested for their ability to affect [3H]GABA efflux. The results indicated that compounds which inhibit GABA uptake into glial cells were also able to stimulate [3H]GABA efflux from these cells.The results are discussed with reference to possible mechanisms involved in the release of GABA from glial cells.

Sodium and lithium movements and axonal function in cockroach nerve cords

Exposure to sodium-deficient (tris) saline caused an appreciable decline in the sodium content of intact connectives in the absence of equivalent reduction in the amplitude of the recorded action potentials. Return of sodium-depleted connectives to normal saline resulted in a rapid recovery of axonal function despite only a partial (less than 70%) recovery in sodium content. Replacement of sodium ions by those of lithium in the bathing medium resulted in a substantial accumulation of this cation. Lithium movements exhibited a marked asymetry, no significant decline in concentration being observed upon return to normal saline. These results are tentatively interpreted in terms of an exchangeable glial sodium fraction and are discussed in relation to extra-axonal sodium regulation.

Ion exchange of the transition metal ions Mn2+, Co2+, and Ni2+ in synthetic zeolites NaX and NaY

Abstract The exchange of Mn2+, Co2+, and Ni2+ in zeolites X and Y has been studied. At 25 °C, these metal ions cannot replace sodium ions present in the network of smaller cavities of both the zeolites. It is possible to describe the ion exchange data by a mathematical equation. The mathematical model assumes two groups of active sites in the supercages.

Studies on the mechanism of uptake of d-glucose by Tetrahymena pyriformis GL

1. 1. The time course of glucose uptake by undisturbed cultures of Tetrahymena pyriformis showed different patterns according to days after inoculation of cells. 2. 2.The glucose uptake was dependent on sodium concentration in the medium, excepting for the initial stage of the uptake. On replacing sodium ions by lithium ions, the uptake of glucose was greatly inhibited to almost the same level as in the medium of Tris ions. 3. 3.The high Q 10°C, the competitive interaction between glucose and fructose, the competitive effect of phlorizin, the effect of 2,4-dinitrophenol and counter-flow suggest that the glucose uptake of T. pyriformis is conducted by an active carrier-mediated process.

A quantitative study of the ionic basis of extraneuronal potential changes in the central nervous system of the cockroach (Periplaneta americana L.).

ABSTRACT Measurements have been made of the extraneuronal potential changes produced by replacement of sodium ions with other organic and inorganic cations in the solution bathing isolated abdominal connectives. On the basis of the observed extraneuronal potential changes it is possible to arrange monovalent cations in the following sequence of effectiveness: It is concluded that the ionic dependence of the extraneuronal potentials is similar to that of a theoretical model system consisting of a perineurial diffusion barrier in series with a long, narrow channel representing the system of intercellular clefts connecting the inwardly facing surface of the perineurium with the extraaxonal fluid. On the basis of this model the effect of high external concentrations of, for example, potassium ions would be to depolarize the outwardly facing perineurial cell membranes. The considerable departure of the observed potentials from the values predicted by the Nernst equation can be accounted for in terms of the short-circuiting effect, due to the finite ionic permeability of the tight junctions between perineurial cells. Qualitative predictions can also be made concerning the rates of movement of potassium and sodium ions in the extracellular system.

Cation positions in cerium X zeolites

The cation positions and the resulting changes, which were caused by the replacement of sodium ions by cerium ions, in the zeolite framework of cerium exchanged 13X-type molecular sieves, 0.3 Na 2O · 13.0 Ce 2O 3 · 44.0 Al 2O 3 · 104.0 SiO 2 · n H 2O 1, have been determined by structural studies using X-ray powder data. In the exchanged sieve ( a 0 = 25.10 ± 0.02 A ̊ ), in which nearly all of the remaining 2% of sodium oxide has been removed by (NH 4SO 4 exchange, cerium ions were found to partially occupy site S4 in the large cavity and site S2 in the sodalite cage. When this material was calcined at 540 ° C in a nitrogen atmosphere ( a 0 = 24.94 ± 0.02 A ̊ ), the cerium cations were found to migrate to sites S1, S2, and S5 with the majority of the cations being in S2. Site S1 is in the hexagonal prism and is the least accessible site. Upon dehydration of the material at 540 ° C in air ( a 0 = 24.86 ± 0.02 A ̊ ), however, the cations moved to sites S1 and S2 only, with the majority of them being in S2 sites. The three cations (on the average) per sodalite cage which occupied S2 sites displayed a strong repulsion for each other. This repulsion resulted in a significant distortion of the sodalite cage. The greater cationic repulsion observed when calcination was done in air versus a much lesser repulsion when calcination was done in a nitrogen atmosphere is due to the oxidation of at least 50% of the Ce 3+ cations to the 4+ oxidation state. For the hydrated sample the occupancy factor of S4 sites is 0.66. The population parameter of S2 is 0.69 and 0.74 for the nitrogen calcined zeolite and for the air calcined zeolite with the corresponding closest CeO distances for this site being 2.56 and 2.66 Å, respectively.

Ion-exchange equilibria of synthetic 4A zeolite with Ni2+, Co2+, Cd2+and Zn2+ions

Linde 4A zeolite was converted to Ni, Co, Zn and Cd forms by replacing sodium ions with divalent cations. The replacement was from 82%(Ni) up to 100%(Cd). Chemical, T.G.A., D.T.A. and X-ray analysis of the divalent metal zeolites have been made and data on the composition of the unit cells and the thermal stability of the lattices were obtained. Ni-zeolite is unstable, its crystal lattice being completely destroyed above 70°C, whereas Co-, Zn- and Cd-zeolites are stable up to 750–850°C. The adsorption of water on the latter zeolites is reversible. Ion-exchange isotherms for Co2+, Zn2+ and Cd2+ at three temperatures were obtained and the thermodynamic functions, ΔG°, ΔH° and ΔS°, of the ion-exchange equilibria calculated. The thermodynamic data are discussed with respect to hydration and size of the cations. A possible explanation of the instability of Ni-zeolite is suggested.

Reactions of n-butene over a nickel exchanged 13X-type zeolite

The isomerization of n-butenes has been studied in a static system using as catalysts zeolites of the 13X-type with different extents of replacement of sodium ions by nickel ions. The presence of nickel enhances the catalytic activity considerably, comparable reaction rates with the nickel-containing zeolites being observed at temperatures 200 K lower than with the parent Na13X.A striking feature of the but-1-ene reaction was the preferential formation of trans-but-2-ene, which is compatible with a reaction involving radical intermediates. Further evidence in support of a radical, rather than a carbonium ion, mechanism was obtained by observing the isomerization (a), in the presence of deuterium (when an enhancement of rate and extensive exchange were observed) and (b), in the presence of deuterium oxide (when very little exchange occurred and the reaction rate was fractionally reduced).Detailed analysis of the exchange products in the reaction of but-1-ene and deuterium over the NiX catalysts, where butane was a major product, suggested that all three butenes exchange at rates which are comparable to the rates of isomerization, and that the hydrogenation process involves a very substantial redistribution of H and D atoms between the molecules.

Influence of lithium ions on the electrical activity of nerve cells of the leech

The influence of lithium ions on the electrical activity of the nerve cells of the leech,Hirudo medicinalis, was investigated by the method of microelectrode recording. It was discovered that the electrical activity of the giant nerve cells disappears rapidly in a solution with lithium ions. In such a solution, the membrane of these cells is depolarized by 5–7 mV; however, polarization of the cells with direct current does not lead to a restoration of their activity. Possible mechanisms of the inability of lithium ions to replace sodium ions in the generation of the action potentials of leech nerve cells are discussed.

Catalytic exchange of benzene with deuterium and allied reactions on X-type molecular sieves containing nickel ions

The exchange of benzene and deuterium has been studied in a static system using as catalysts molecular sieves of the X type with different extents of replacement of sodium ions by nickel ions. The rate of reaction at 170°C rose by a factor of more than 105 as the nickel content was increased to one ion per 8 cages but remained constant with further ion-exchange. The catalytic activity of sieves, particularly those of low nickel content, outgassed at 420°C was reduced by addition of a small quantity of water (one molecule per three cages) at room temperature. The exchange of the three xylenes and toluene with deuterium was studied on NiX (1), a sieve containing 2.95 nickel ions per cage. In all cases, the side-group hydrogen atoms were replaced more rapidly than the ring atoms but with the xylenes all the ring atoms reacted at similar rates independent of molecule or position and no steric effects were observed. With toluene, three ring atoms reacted more rapidly than those of the xylenes and two more slowly. Hydrogen-deuterium exchange occurred rapidly on NiX (1) at 85°C but the exchange of benzene with sorbed deuterium oxide was slow at 300°C. NiX (1) treated for 30 min at 300°C with hydrogen developed reversible colour changes, an e.s.r. signal and enhanced catalytic activity for the exchange of benzene but reverted to normal behaviour on evacuation for 30 min at 300°C.

The role of cations in conduction in the central nervous system of the herbivorous insect Carausius morosus

1. The role of cations in nervous conduction in the central nervous system of the herbivorous insect Carausius morosus was studied with external electrodes. 2. The size of the compound action potential in axons (totally desheathed connectives) depends on the sodium concentration of the bathing medium (Fig. 2), the relationship roughly approximating that predicted by the Nernst formula (Table 4). 3. Sodium-free bathing medium reversibly blocks conduction in axons (totally desheathed connectives) within 1 min (Fig. 2). 4. At low concentrations in the perfusion solution, both tetrodotoxin and procaine reversibly block conduction in axons within a few minutes. 5. Lithium ions replace sodium ions in the maintenance of action potential size in axons for about 10 min, but then action potentials gradually decline. The action potential size is restored when the nerve cord is perfused once again with a medium containing the initial sodium concentration (Fig. 3). 6. External sodium concentrations either higher than 180 mM or lower than 150 mM significantly decrease the viability of axons (Fig. 4); we concluded that the sodium concentration of the extracellular fluid of the nerve cord is probably between 150 and 180 mM. 7. The order of effectiveness of potassium, rubidium and cesium ions in suppressing compound action potentials in axons is K+= Rb+>Cs+ (Fig. 5). 8. The action potentials in axons perfused with a solution containing 27 mM K+ are reversibly suppressed by approximately 37%; we concluded that the potassium concentration in the extracellular fluid of the ventral nerve cord is less than 27 mM. 9. When the calcium concentration in the external medium is reduced from 7.5 to 1 mM, repetitive firing and progressive conduction blockage are produced after nearly 4 hr in connectives in the absence of a fat-body sheath (Fig. 6). 10. When manganous ions (16 mM) are added to the bathing medium, there is little change in the level of axonal electrical activity (Fig. 7). Since manganous ions have been shown to suppress the increase in membrane conductance to calcium during the so-called calcium spikes of some irritable tissues, we concluded that calcium ions do not contribute significantly to the inward current during the action potential. 11. Axonal viability increases with the external magnesium concentration in the range from 0 to 50 mM Mg++ (Fig. 8). However, the actual magnesium concentration of the extracellular fluid may be between 10 and 25 mM. 12. When axons are perfused with magnesium-free solution, the action potentials are reduced to one-half of their initial size only after 2.36±0.42 hr; we concluded that magnesium ions are not carriers of inward current during action potentials. 13. Comparing our data with published data obtained from other animals, we concluded that nervous conduction in Carausius conforms to the classical membrane theory despite the unusual cationic levels in the hemolymph and that a yet undefined homeostatic mechanism maintains extracellular cationic concentrations at favorable levels in the nerve cord. 14. Viability studies indicate that an active transport mechanism is probably located in the fat-body sheath and that this mechanism probably maintains the extracellular sodium concentration at a high level (Table 2). These studies also indicate that the neural lamella and perineurium form a diffusion barrier which is only slightly permeable to the common cations (Tables 2, 3 and Fig. 6). 15. A model (Fig. 9), explaining the regulation of cationic concentrations in the extracellular fluid of Carausius nerve cord, is proposed from available data.