Role Of Sodium Ions Research Articles

The role of sodium in mediating adrenocorticotropin secretion by perifused rat anterior pituitary cells.

We studied the role of sodium ions in mediating basal and stimulated ACTH release from perifused rat anterior pituitary cells by exposing the cells to the sodium channel opener veratridine or the Na+/K(+)-adenosine triphosphatase inhibitor ouabain to increase the intracellular Na+ concentration or, conversely, by omitting Na+ from the perifusion medium or blocking Na+ entry into the cell with tetrodotoxin, a voltage-dependent sodium channel blocker, to decrease the intracellular Na+ concentration. Neither tetrodotoxin nor Na(+)-free medium had a significant effect on 100 nM arginine vasopressin (AVP) or 10 nM ovine corticotropin-releasing hormone (CRH)-induced ACTH secretion. Veratridine increased basal ACTH secretion by 122% (41.3 +/- 2.9 vs. 18.6 +/- 0.4 pg/min; P < 0.001), the initial spike phase of the response to AVP by 65% (0.28 +/- 0.01 vs. 0.17 +/- 0.03 ng/3 min; P < 0.005), the subsequent sustained phase to AVP by 129% (0.16 +/- 0.01 vs. 0.07 +/- 0.01 ng/7 min; P < 0.005), and the total response to CRH by 70% (0.39 +/- 0.01 vs. 0.23 +/- 0.04 ng/10 min; P < 0.05). Ouabain increased basal ACTH secretion by 39% (45.7 +/- 2.8 vs. 32.9 +/- 2.1 pg/min; P < 0.05), the initial spike phase of the response to AVP by 88% (0.32 +/- 0.02 vs. 0.17 +/- 0.01 ng/3 min; P < 0.005), the sustained phase response to AVP by 67% (0.10 +/- 0.01 vs. 0.06 +/- 0.01 ng/7 min; P < 0.05), and the total integrated response to CRH by 49% (0.88 +/- 0.09 vs. 0.59 +/- 0.03 ng/10 min; P < 0.05). However, the effects of both veratridine and ouabain on basal ACTH secretion were significantly attenuated in Ca(2+)-free EGTA-containing medium, suggesting that this effect was indirect, due to membrane depolarization and consequent influx of extracellular Ca2+. Dexamethasone (100 nM) had no effect on the ACTH response to either veratridine or ouabain. We conclude that changes in the intracellular Na+ concentration and sodium channel activity are not directly involved in AVP- or CRH-induced ACTH secretion.

Role of sodium ions for sulfate transport and energy metabolism in Desulfovibrio salexigens

Role of sodium ions for sulfate transport and energy metabolism in Desulfovibrio salexigens

Properties of microfiltration membranes: Adsorption of bovine serum albumin at polyvinylidene fluoride membranes

The adsorption of bovine serum albumin at polyvinylidene fluoride microfiltration membranes has been studied as a function of protein concentration, pH, electrolyte type, and flow rate through the membrane. Adsorption is initially rapid. Equilibrium is achieved after a period of 30 min to 3 h. Adsorption isotherms indicate two different adsorption sites, one of high affinity and the other of lower affinity for the protein. The numbers of such sites and the appropriate binding constants have been determined. The saturation coverage of the membranes by the protein occurs at substantially less than a monolayer. The variation of the amount of protein adsorbed with pH and electrolyte strength indicates that both electrostatic and short range forces need to be considered. The data show that the role of calcium ions is different from the role of sodium ions, possibly due to calcium bridging between carboxyl groups of the protein and the membrane surface.

A Method To Disperse Aggregates of a Flocculent Yeast for Photometric Analysis

AbstractStrategies to disperse aggregates so the cells remain in suspension long enough to take stable absorbance readings are studied. The optical density of highly flocculating yeasts, such as Saccharomyces cerevisiae ATCC 26603, drops because of cells settling to the bottom in less than 1 min. It presents a problem in using turbidimetric measurement for cell density estimate. Dilution of the yeast samples with sodium salts in a wide range of concentrations (10 mM to 1 M) disperses the aggregates, whereas dilution with calcium salts does not. ζ‐Potential measurements indicate that sodium disperses the yeast flocs by reversal of the charges on the cell surfaces. An attempt is also made to resolve the controversy about the role of sodium ions in flocculation.

The role of sodium ions in methanogenesis

Cell suspensions of Methanosarcina barkeri were found to oxidize formaldehyde to CO2 and 2H2 (delta G0' = -27 kJ/mol CO2), when methanogenesis was inhibited by 2-bromoethanesulfonate. We report here that this reaction is coupled with (a) primary electrogenic Na+ translocation at a stoichiometry of 2-3 Na+/CO2, (b) with secondary H+ translocation via a Na+/H+ antiporter and (c) with ATP synthesis driven by an electrochemical proton potential. This is concluded from the following findings. Formaldehyde oxidation to CO2 and 2H2 was dependent on Na+ ions, 2-3 mol Na+/mol formaldehyde oxidized were extruded. Na+ translocation was inhibited by Na+ ionophores, but not affected by protonophores of Na+/H+ antiport inhibitors. Formaldehyde oxidation was associated with the build up of a membrane potential in the order of 100 mV (inside negative), which could be dissipated by sodium ionophores rather than by protonophores. Formaldehyde oxidation was coupled with ATP synthesis, which could be inhibited by Na+ ionophores, Na+/H+ antiport inhibitors, by protonophores and by the H+-translocating-ATP-synthase inhibitor, dicyclohexylcarbodiimide. With cell suspensions of Methanobacterium thermoautotrophicum similar results were obtained.

On the role of sodium ions in the regulation of the inward-rectifying potassium conductance in cat ventricular myocytes.

The conductance of the inward-rectifying K+ current (IK1) in isolated cat ventricular myocytes is decreased by reducing the extracellular Na+ concentration. Using a whole-cell patch-clamp technique, possible mechanisms underlying this Na+ dependence were investigated. These included (a) block of inward K+ current by the Na+ substitute, (b) changes in membrane surface charge associated with removal of extracellular Na+, (c) increases of intracellular Ca2+ due to suppression of Na-Ca exchange, (d) reduction of a Na+-dependent K+ conductance due to a subsequent decrease of intracellular Na+, (e) reduction of IK1 conductance (gK1) associated with reduction of intracellular pH due to suppression of Na-proton exchange. The findings support the hypothesis that the effect of removing Na+ is mediated through a decrease in intracellular pH. These include observations that: (a) reducing internal pH by reducing external pH caused a decrease in gK1, and the conductance changes caused by reducing extracellular pH and removing extracellular Na+ were not additive: (b) the effect of reducing pHo was attenuated by dialyzing with a low pH internal solution; (c) gK1 was reduced by exposure to the Na-proton exchange inhibitor dimethylamiloride, and this effect was absent in the absence of Na+. These findings imply that physiological or pathological processes such as ischemia and metabolic or respiratory acidosis which can produce intracellular acidosis should be expected to affect K+ permeation through the IK1 channel.

Examination of the relationship between the uptake site for 5-hydroxytryptamine and the high affinity binding site for [ 3H]imipramine II : The role of sodium ions

Exogenous sodium ions stimulated both the high affinity binding of [ 3H]5-imipramine to membranes from the cortex of the rat and the high affinity accumulation of [ 3H]5-hydroxytryptamine (5-HT) into synaptosomes from the cortex of the rat with similar potencies. Imipramine and zimelidine inhibited synaptosomal uptake of [ 3H]5-HT potently in standard Tris-Krebs medium, but in a low-sodium medium their inhibitory potencies were significantly attenuated. The inhibitory potencies of panuramine and exogenous 5-HT on the uptake of [ 3H]5-HT were not significantly affected whether the uptake was measured in a normal or low-sodium Tris-Krebs. Imipramine and zimelidine were potent blockers of high affinity binding of [ 3H]imipramine whereas panuramine and 5-HT only inhibited the binding of [ 3H]imipramine at concentrations in excess of those required to inhibit the uptake of [ 3H]5-HT. It is suggested that imipramine inhibits the uptake of 5-HT by a sodium-dependent action probably at the high affinity binding site for [ 3H]imipramine, whereas panuramine and 5-HT inhibit the uptake of 5-HT by a sodium-independent mechanism at a site other than the binding site for [ 3H]imipramine.

Effects of sodium ions and monensin on amylase secretion from rat parotid cells

The role of sodium ions in amylase secretion from rat parotid cells was studied using various Na +-free media and monensin. In a sucrose medium, amylase secretion was not stimulated by isoproterenol but was significantly stimulated by dibutyryl cAMP. In choline chloride and LiCl media, both isoproterenol and dibutyryl cAMP clearly evoked amylase release. Monensin itself elicited amylase secretion slightly, but significantly inhibited the secretion stimulated by isoproterenol or dibutyryl cAMP. The inhibitory effect of monensin was detectable even in choline chloride, LiCl and KCl media. These results indicate that sodium ions are not essential for amylase secretion from rat parotid cells and that the inhibitory effect of monensin is independent of influx of sodium ions or efflux of potassium ions.

Effects of sulpiride and apomorphine on prolactin release in adrenalectomized animals. Role of sodium ions

The present experiments were performed to demonstrate in vivo the existence of a modulatory role of Na + in the inhibitory control of prolactin (PRL) secretion. Groups of adult male rats were either adrenalectomized (adrenex) or sham-operated (normals) and implanted in the right atrium with a chronic cannula for the infusion of solutions or the sequential withdrawal of blood samples. Four days later, adrenex rats were infused for 1 h with either saline 0.9% or dextrose 5.6% (310 mOsm/kg H 2O) at the rate of 10 ml/kg/h from Time −60 min until Time 0 min. All animals were injected at Time −45 min with sulpiride 0.05 mg/kg. At Time 0 min, some animals received apomorphine 5 mg/kg while others received a 0.05 mg/kg dose of the drug. Blood samples were obtained at −45, −30, −15, 0, 5, 10, 20 and 30 min for PRL assay. Plasma Na + concentration was measured at −45, 0 and 30 min and plasma osmolarity at 0 min in adrenex rats. In normal controls plasma Na + values were measured at the end of the experiment. Binding values ( K D and B max) of pituitary D 2-receptors were measured in adrenex and sham-operated rats using [ 3H]spiroperidol as ligand and d-butaclamol to define non-specific binding. Plasma Na + values remained constant in saline-infused adrenex rats and similar to those of normal controls, while in dextrose-infused adrenex rats they fell progressively during the experimental period and were always lower than in the two other groups. Plasma osmolarity was similar in the two adrenex groups. Sulpiride induced a much greater rise of plasma PRL values in iso-than in hyponatremic adrenex or normal animals. Apomorphine 5 mg/kg exerted a biphasic action on PRL release in adrenex rats, stimulatory first and then inhibitory, but only an inhibitory effect in normal animals. While the inhibitory action of this dose of the drug was similar in all animals, the stimulatory effect was greater in iso- than in hyponatremic adrenex rats. A 0.05 mg/kg dose of apomorphine had only a stimulatory effect in adrenex rats, which was greater in the isonatremic group, but was completely ineffective in normal rats. Binding studies showed the presence of D 2-receptors with a greater binding affinity in the anterior pituitaries of adrenex than in those of normal rats. These results indicate that adrenalectomy enhances the PRL-releasing effect of sulpiride, a dopamine antagonist, probably by sensitizing the postsynaptic D 2 receptor and that hyponatremia may antagonize such an enhancing effect. In conclusion, both the adrenal gland and Na + may intervene in the modulation of the inhibitory control pituitary PRL release.

Role of sodium ion in transport of folic acid in the small intestine

The effect of sodium on folate transport across the intestinal luminal membrane was analyzed using two techniques: the "influx" chamber and isolated brush-border membrane vesicles. Preincubation of tissue in Na+-free medium did not have a consistent effect on folic acid influx provided that Na+ was present in the test solution. Replacement of Na+ in the test solution by choline+ resulted in a significant reduction of folic acid influx. However, when intestinal sheets that had been equilibrated in Na+-free solution were exposed to test solution containing either Na+, Li+, K+, Rb+, Cs+, Tris+, or guanidinium+ as main cations, folic acid influx was not significantly decreased. Concentration-dependence studies showed that replacement of Na+ by Rb+ did not affect the saturable mechanism of folate transport. Rather, a decrease in nonsaturable folic acid uptake accounted for the slightly reduced influx observed in the presence of Rb+. Experiments with brush-border membrane vesicles revealed that methotrexate uptake was significantly higher in the presence of external Na+ than in the presence of K+, but was not different from uptake in the presence of K+ plus valinomycin. These data suggest that the saturable component of folate transport is not Na+ dependent, and nonsaturable transport of folic acid across the luminal membrane occurs in part through a conductive pathway that involves a negatively charged species of folate and a cation whose membrane permeability affects the rate of folate transport. The importance of Na+ in this process in vivo derives from the fact that Na+ is the most permeant cation available at the absorptive site in the small intestine.

Mechanism of ATP sythesis and role of sodium ions in Methanosarcina barkeri growing on methanol

Summary Methanogensis by Methanosarcina barkeri according to the equation CH 3 OH + H 2 → CH 4 + H 2 O was associated with the generation of a membrane potential (ΔΨ) across the cytoplasmic membrane and with ATP synthesis. ΔΨ and the formation of ATP were abolished by the uncoupler tetrachlorosalicylanilide, but methanogenesis was not affected. N,N′-dicyclohexylcarbodiimide, an inhibitor of the protontranslocating ATPase, caused rapid exhaustion of the ATP pool and discontinuation of methanogenesis, whereas ΔΨ remained unaffected under these conditions. Methanogenesis from CH 3 OH + H 2 as well as ATP synthesis proceeded in the absence of Na + . It is concluded from these results that ATP is synthesized during methanogenesis by a chemiosmotic mechanism coupled to the methylcoenzyme M methylreductase and that Na + is not involved in this process. In contrast, methanogenesis according to the equation 4 CH 3 OH → 3 CH 4 + CO 2 + 2 H 2 O was completely inhibited by the uncoupler tetrachlorosalicylanilide and exhibited a requirement for Na + . The Na + requirement and the uncoupler sensitivity could be relieved by the addition of formaldehyde. It is concluded from these results that the oxidation of methanol to the level of formaldehyde proceeds only at an energized membrane and that Na + is required for this reaction.

L-tyrosine and L-tryptophan transport in red blood cells in normal subjects. Effects of other amino acids, temperature and medium of incubation.

Blood cells may be used as a model in the central transport mechanisms of amino acids, precursors of amines, implicated in some hypotheses of psychiatric diseases. In a previous paper, we showed a deficit of tyrosine transport by red cells incubated in the plasma of depressed patients. In the present study, we have investigated the interaction of these peripheral transport mechanisms for tyrosine and tryptophan with other amino acid transports, such as the L and ASC systems, and the role of sodium ions in the extracellular medium. We also describe the inhibition induced by incubation at a low temperature, and a probable role of the membrane viscosity. The interest of incubating the cells in their own plasma, in order to have physiological conditions, is also discussed.

Cation exchange--a common mechanism in the storage and release of biogenic amines stored in granules (vesicles)? III. A possible role of sodium ions in non-exocytotic fractional release of neurotransmitters.

The matrices of the amine storing granules in mast cells, chromaffin cells and noradrenergic nerves show properties reminiscent of cation exchanger materials. In vitro, the amines are released from their granule storage sites on exposure of the granules to cations, e.g. sodium ions. The proposal is made that also in vivo the release of transmitter amines is the result of cation exchange Amine+ in equilibrium Na+ ions and that the release of transmitter amines occurs as a nonexocytotic fractional release engaging multiple granules instead of exocytotic emptying of a few. Some physiological and pharmacological implications of a fractional transmitter release are discussed.

SODIUM REQUIREMENTS IN HARDENING OF THE FERTILIZATION ENVELOPE AND EMBRYONIC DEVELOPMENT IN SEA URCHINS

The role of sodium ions in fertilization and development of sea urchin (Arbacia punctulata and Strongylocentrotus purpuratus) eggs was studied by culturing eggs and embryos in low sodium (choline-substituted) sea water. Hardening of the fertilization envelope was impaired in 19 mM Na+ as indicated by the collapse of this investment 30-60 min after insemination. Cross-linking of the fertilization envelope, assayed in terms of the onset of resistance to dispersal by isotonic urea, was not affected by low sodium. However, impregnation of the fertilization envelope by structural proteins derived from the egg's cortical granules did not take place in low sodium. The "I-T" transition in the configuration of the fertilization envelope in Strongylocentrotus from "igloo" shaped casts of microvilli that were at the surface of the unfertilized egg to sharp "tent" shaped spikes also was prevented in low sodium. Potassium and lithium effectively substituted for sodium in promoting the normal structuralization of the fertilization envelope, while choline and Tris did not. Fertilized eggs divided more slowly in low sodium than in normal (419-425 mM Na+) sea water. Arbacia embryos fertilized and cultured in low sodium sea water showed a reversible developmental arrest at the swimming blastula stage. This finding suggests that a sodium activated switch initiates gastrulation (differentiation) in sea urchins. Taken together, these results show that sodium is essential for several physiologic processes related to fertilization and developmental in sea urchins, in addition to the previously described rapid-electrical block to polyspermy and the coupling of early and late events in egg activation.

The role of sodium ions in pancreatic fluid secretion in the rabbit.

1. NaCl in the bathing medium of the isolated rabbit pancreas has been gradually replaced by isotonic amounts of either sucrose, choline chloride or KCl. 2. The replacement of NaCl always leads to a reduction in pancreatic flow. This reduction is largest with sucrose as replacing agent and smallest with KCl. 3. The Na+ concentration in the secreted fluid decreases only slightly when NaCl is replaced by sucrose. In the experiments with choline chloride, the Na+ concentration in the secreted fluid decreases slightly when less than 60 mM-NaCl has been replaced, but decreases markedly after more extensive NaCl replacement. Upon replacement of NaCl by KCl, the Na+ concentration in the secreted fluid is always equal to that in the bathing medium. 4. The K+ concentration in the secreted fluid increases by 8 mM upon replacing NaCl by either sucrose or choline chloride. Upon replacement by KCl the K+ concentration in the secreted fluid is always approximately equal to that in the bathing medium. 5. There is a linear relationship between the ratio of the K+ concentrations in the secreted fluid and the bathing medium and the ratio of the Na+ concentrations in these fluids. 6. Replacement of NaCl in the bathing medium does not lead to a change in the transepithelial potential. 7. The secreted fluid is always isotonic with that of the bathing medium; in the case of an extensive replacement of NaCl by either sucrose or choline chloride isotonicity is maintained by a higher cation concentration and an increased appearance of the replacing agents in the secreted fluid. 8. These studies confirm previous findings that extracellular Na+ is essential for pancreatic fluid secretion. 9. They also indicate that the monovalent cations reach the secreted fluid through a paracellular pathway. 10. These findings are incorporated in a model for the electrolyte movements involved in the pancreatic fluid secretion by ductular as well as by acinar cells.

Role of sodium ion in renal transport of p-aminohippurate in vitro.

Role of sodium ion in renal transport of p-aminohippurate in vitro.

Role of sodium ions in [formula omitted] transport by newt kidney

1. 1. The effect of external Na + concentration on p- amonohippurate uptake by isolated kidneys of newt ( Triturus pyrrhogaster) was studied kinetically and electrophysiologically. 2. 2. p- Aminohippurate uptake conformed to Michaelis-Menten type kinetics in regard to both p- aminohippurate and Na + concentration in the incubation medium. Kinetic studies revealed that reduction of Na + concentrations increased the values of K t without altering the maximal rate ( V) of p- aminohippurate uptake. The values of K t were a linear function of the reciprocal of Na + concentration. These results suggest the presence of interaction between p- aminohippurate and Na + at the carrier level, i.e. Na +-coupled cotransport. 3. 3. p- Aminohippurate had no effect on the electrical potential difference across the peritubular membrane in both 10 and 100 mM Na + solutions, suggesting that p- aminohippurate is transported across the peritubular membrane in a form of electrically neutral carrier complex. This is consistent with the results of the kinetic studies. 4. 4. p- Aminohippurate uptake was proportional to the electrochemical potential gradient of Na + ( Δ μ Na ) across the peritubular membrane. This result indicates that the maintenance of sufficient Δ μ Na appears to be necessary for the accumulation of p- aminihippurate against its electrochemical potential gradient, supporting Na + gradient hypothesis.

The role of sodium ions in ATP formation by the sodium pump

A study has been made to characterize ATP synthesis from ADP and P 1 by the sodium pump with membranes isolated from rabbit kidney. Incorporation of 32 P 1 into ATP was measured. ATP was not formed in a one-step reaction. Synthesis was dependent upon two separate incuba­tions in which incorporation of P 1 into phosphoprotein was followed by transfer of phosphate to ADP. The experimental conditions for the first reaction were different from those for the second (phosphate transfer) reaction. The latter took place only when a high Na concentration (at least 0.5 M) was added. ATP formation was prevented by both K and ouabain. The sequence of reactions could be repeated after washing to remove Na ions, indicating that the driving force for the reactions could be regenerated. The dissipation of ionic gradients was not involved because the Lubrol-solubilized pump was also able to synthesize ATP. It was concluded that the energy for ATP synthesis was derived from specific and reversible interactions of Na ions with the pump. The reactions for ATP synthesis by the sodium pump have been summarized in the form of a cycle.

61) - Role of sodium ion in secretion of catecholamine from perfused bovine adrenals

61) - Role of sodium ion in secretion of catecholamine from perfused bovine adrenals

Studies on the Action of Na on Insulin Release I: Role of Sodium Ion in the Mechanism of Insulin Release in View of Suppressive Effect of Diphenylhydantoin

Studies on the Action of Na on Insulin Release I: Role of Sodium Ion in the Mechanism of Insulin Release in View of Suppressive Effect of Diphenylhydantoin