Selenium prevents mercuric chloride induced acute osmoregulatory failure without glutathione peroxidase involvement in the black bullhead (Ictalurus melas)

The relationship between coelomic injections of mercuric chloride doses and osmoregulatory responses was measured. Response parameters were weight increases and blood osmolarity decreases 72 hr after dose administration. Massive edema and large decreases in blood osmolarity could be completely prevented by subcutaneous injections of equimolar sodium selenite. Mercury induced damage did not involve alterations of either selenium-dependent or non-selenium-dependent glutathione peroxidase activities.     

Effect of osmolarity on potassium transport in isolated cerebral microvessels

Potassium transport in microvessels isolated from rat brain by a technique involving density gradient centrifugation was studied in HEPES buffer solutions of varying osmolarity from 200 to 420 mosmols, containing different concentration of sodium chloride, choline chloride, or sodium nitrate. The flux of 86Rb (as a tracer for K) into and out of the endothelial cells was estimated. Potassium influx was very sensitive to the osmolarity of the medium. Ouabain-insensitive K-component was reduced in hypotonic medium and was increased in medium made hypertonic with sodium chloride or mannitol. Choline chloride replacement caused a large reduction in K influx. Potassium influx was significant decrease when nitrate is substituted for chloride ion in isotonic and hypertonic media, whereas a slight decrease was found in hypotonic medium. The decrease of K influx in the ion-replacement medium is due to a decrement of the ouabain-insensitive component. Potassium efflux was unchanged in hypotonic medium but was somewhat reduced in hypertonic medium. The marked effect of medium osmolarity on K fluxes suggests that these fluxes may be responsible for the volume regulatory K movements. The possible mechanism of changes of K flux under anisotonic media is also discussed.     

Osmoregulation in Rhizobium meliloti: inhibition of growth by salts

A defined medium of low osmolarity was developed permitting growth of Rhizobium meliloti with generation times of approximately 2.8 h doubling^-1. The effects of sodium, potassium, magnesium, ammonium, chloride, sulfate, phosphate, bicarbonate and acetate ions on the growth rate of R. meliloti were determined. Sodium, potassium and ammonium ions had little effect on growth at concentrations of 100 mEq or less; magnesium ion inhibited growth severely at concentrations of 50 mEq (25 mM). Of the anions, chloride and sulfate appeared to have little effect while phosphate, bicarbonate, and acetate inhibited growth at concentrations of as little as 25 mEq. The addition of proline, glutamate, or betaine to cells growing in inhibitory concentrations of NaCl did not relieve the inhibition. When grown in the presence of inhibitory levels of NaCl, the intracellular concentration of glutamate but not of proline or gamma amino butyric acid increased 5-fold.     

Changes in blood osmolarity,electrolytes, and metabolites among adult rats treated with a neurotoxic dose of MSG1

Adult rats were given large doses of MSG (4 g/kg) or isosmolar amounts of sodium chloride or L-alanine intraperitoneally or by forced intubation. Blood or plasma samples from these rats where assayed for osmolarity, hematocrit, pH, and concentrations of protein, sodium, potassium, chloride, calcium, magnesium, and urea nitrogen. Intraperitoneal MSG produced characteristic hypothalamic lesions; MSG by gavage failed to do so. Intraperitoneal MSG also caused major increases in plasma osmolarity, hemoconcentration, hypovolemia, alkalosis, hypernatremia, and uremia; plasma levels of chloride and potassium fell significantly. Administration of MSG by gavage caused much smaller changes in plasma osmolarity and sodium, and no significant changes in hematocrit, plasma protein or plasma urea nitrogen. Administration of sodium chloride or L-alanine (agents not known to produce the characteristics MSG brain lesions) caused some, but not all, of the metabolic changes seen after MSG. These observations suppot the hypothesis that the ability of large, concentrated doses of MSG to produce brain lesions in susceptible species involves a two-step process, i.e., initial damage to the blood-brain barrier for glutamate, followed by entry of the circulating amino acid into the extracellular space of the brain.     

Replacement of potassium chloride by potassium glutamate dramatically enhances protein-DNA interactions in vitro

Although protein-nucleic acid interactions exhibit dramatic dependences on both ion concentration and type in vitro, large variations in intracellular ion concentrations can occur in Escherichia coli and other organisms without apparent effects on gene expression in vivo. E. coli accumulates K+ and glutamate as cytoplasmic osmolytes. The cytoplasmic K+ concentration in E. coli varies from less than 0.2 to greater than 0.9 m as a function of external osmolarity; corresponding cytoplasmic glutamate concentrations range from less than 0.03 to greater than 0.25 m. Only low levels of chloride occur in the cytoplasm of E. coli at all osmotic conditions. Since most in vitro studies have been performed in chloride salts, whereas glutamate is the more relevant physiological anion, we have measured the effects of the substitution of potassium glutamate (KGlu) for KCl on the kinetics and equilibria of a variety of site-specific protein-DNA interactions in vitro. Both the interaction of E. coli RNA polymerase with two phage lambda promoters and the interactions of various restriction enzymes with their DNA cleavage sites are enhanced by this substitution. Using the abortive initiation assay, we find a greater than 30-fold increase in the second-order rate constant for open complex formation at the lambda PR promoter and a 10-fold increase at the lambda PR' promoter, when KGlu is substituted for KCl. Replacement of KCl by KGlu does not affect the strong salt dependences of these interactions; increasing either KCl or KGlu concentrations decreases both reaction rates and extents. Substitution of glutamate for chloride does, however, shift the range of salt concentrations over which these interactions are observable to higher K+ concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of lithium on biliary electrolyte and bile acid excretion in young and adult rats

The influence of a three-day lithium treatment on the biliary electrolyte and bile acid output was determined in 20- and 105-day-old rats. The osmolarity of bile and the biliary concentrations of cations (Na+, K+, Ca++, H+) and chloride were higher in untreated young rats than in adults, although bile flow and bile acid excretion rates of the young and adult animals were comparable. Lithium increased the biliary excretion of sodium, potassium and calcium and decreased the excretion of chloride and bicarbonate ions in both age groups. In contrast, lithium treatment reduced bile acid excretion only in adult rats. The lithium-induced alterations in biliary ion elimination may be caused by an intracellular replacement of sodium and/or potassium. These results indicate that after lithium treatment cation loss occurs in the young as well as in the adult organism not only via urine and faeces but also via bile.     

THE CHLORIDE CONTENT, ANION DEFICIT AND VOLUME OF SYNAPTOSOMES

—The uptake of ³⁶Cl⁻ into incubated synaptosomes was found to reach a steady state within 30 min enabling estimates of the amount of intra-synaptosomal chloride to be made. There was an excess in the total charge of sodium and potassium over that of chloride within the synaptosomes. This deficit of permeant anions is balanced within the synaptosome by negatively charged protein and other anions such as aspartate and phosphate. Their combined amount could be estimated from the magnitude of the anion deficit. The net valency of the substances causing the anion deficit was determined by relating the ion content to the intra-synaptosomal volume when metabolic activity was blocked. It was found to be similar to that of cerebral cortex tissue in vivo. The intra-synaptosomal volume was found to change so that the osmolarity of the synaptosomal contents equalled the osmolarity of the incubation medium. A method of determining the intra-synaptosomal volume by measuring the ion content is described. The results from this method are compared with those obtained using conventional space markers.     

Influence of Hypotonic Shock on Glutamate and GABA Uptake in Rat Brain Synaptosomes

Hyponatremia leads to hyperexcitability of neurons, seizures, and coma. It is well established that uptake of neurotransmitters is a sodium-dependent process. Therefore, we suggest that inhibition of neurotransmitter uptake can lead to the clinical manifestations of hyponatremia. Decreasing of sodium concentration down to 92 mM in incubation medium, which corresponds to lowering the osmolarity down to 230 mOsm/l, leads to a 45% decrease in glutamate uptake and a 46% decrease in gamma-aminobutyric acid (GABA) uptake. However, this effect was mediated by the nonspecific lowering of osmolarity rather than by decreasing sodium concentration. Hypotonic shock was able to reduce glutamate uptake in the presence of protein kinase inhibitors staurosporine and genistein, the phosphatase inhibitor okadaic acid, the phosphatidylinositol 3-kinase inhibitor wortmannin, and cytoskeleton modulators colchicine and cytochalasin B. Therefore, we suggest that intracellular signaling is not mediating the effect of osmolarity reduction on neurotransmitter uptake.     

The effects of desiccation and rehydration on the lone star tick

This study describes the effects of desiccation and rehydration on the water content, haemolymph volume (per cent), osmolarity, and concentrations of Na, K, Mg, and Ca in the haemolymph of the lone star tick, Amblyomma americanum.The water content percentages of ‘severely desiccated’, ‘moderately’ and ‘fully hydrated’ ticks were 46·0, 52·8, and 60·3 per cent respectively. The lowest and highest of these were near the minimum and maximum possible.The haemolymph volume (per cent) of ‘severely desiccated’ ticks was regulated near the level of ‘moderately hydrated’ ticks despite significant decreases in total body water content and increases in osmolarity and concentration of sodium. Conversely, the change from ‘severely desiccated’ to ‘moderately hydrated’ ticks can be viewed as causing an increase in total body water, decrease in blood osmolarity and sodium, but little change in haemolymph volume (per cent).Most of the water taken up by ‘moderately hydrated’ ticks (while becoming ‘fully hydrated’) was added to the haemolymph. At the same time, there was little change in the blood osmolarity or haemolymph concentration of sodium. Conversely, the change of ‘fully’ to ‘moderately hydrated’ ticks was marked by a substantial loss of haemolymph volume (per cent) but little change in osmolarity and concentration of sodium.The concentration of potassium was regulated over the full range of desiccating and hydrating conditions. The lone star tick appeared less able to regulate its haemolymph concentrations of Ca and Mg; both fluctuated at the same rate, but inversely as the haemolymph volume (per cent).It appears that a carefully controlled movement of solutes (Na the predominant cation) between haemolymph and non-haemolymph tissue is intimately linked with haemolymph volume regulation and movement of water into the haemolymph during hydration.     

Effect of sodium and osmolarity on renin secretion.

The effect of changes in sodium and osmolarity on renin secretion has been studied in the isolated perfused rat kidney. Perfusion with low sodium buffer (110 mM/l) produced a significant increase in renin secretion compared with control experiments (Na+:135 mM/l). Since the presence of tubules seems necessary for such an effect to take place, it suggests that the high renin secretion stimulated by a low sodium buffer centers in the Macula densa. Perfusion with high sodium buffer (170 mM/l; osmolarity 350 mOs/l) induces a stimulation on renin release. However, a greater rise in renin is achieved in control experiments if choline chloride increases the osmolarity from 300 to 350 mOs/l. All this suggests that high sodium buffer, independently of its osmotic effect, has an inhibitory role on renin release.     

Effect of salt composition of the medium and ethanol on cholinesterase hydrolysis of various substrates

Sodium chloride, phosphate buffer and ethanol were studied for their effect on butyryl cholinesterase hydrolysis rate of acetylcholine, acetylthiocholine, butyrylthiocholine and nonion substrate of indophenylacetate. The concentrations of 1.10(-2) = 1.10(-1) M of sodium chloride activated enzymatic hydrolysis of ion substrates at the concentrations lower than 1.10(-4) M but sodium chloride is a competitive inhibitor at higher concentrations. Phosphate buffer also activates substrates enzyme hydrolysis at the concentrations of 2.10(-4) M and lower, but it inhibits incompetitively the nonion substrate indophenylacetate hydrolysis. Ethanol activates butyrylthiocholine hydrolysis and is a competitive inhibitor in acetylthiocholine and indophenylacetate hydrolysis. The observed effects are discussed on the assumption of two forms of butyrylcholinesterase E' and E" existence. These two forms are determined by different kinetic parameters and are in equilibrium.     

GAT1 (GABA:Na+:Cl-) cotransport function. Database reconstruction with an alternating access model.

We have developed an alternating access transport model that accounts well for GAT1 (GABA:Na+:Cl-) cotransport function in Xenopus oocyte membranes. To do so, many alternative models were fitted to a database on GAT1 function, and discrepancies were analyzed. The model assumes that GAT1 exists predominantly in two states, Ein and E(out). In the Ein state, one chloride and two sodium ions can bind sequentially from the cytoplasmic side. In the Eout state, one sodium ion is occluded within the transporter, and one chloride, one sodium, and one gamma-aminobutyric acid (GABA) molecule can bind from the extracellular side. When Ein sites are empty, a transition to the Eout state opens binding sites to the outside and occludes one extracellular sodium ion. This conformational change is the major electrogenic GAT1 reaction, and it rate-limits forward transport (i.e., GABA uptake) at 0 mV. From the Eout state, one GABA can be translocated with one sodium ion to the cytoplasmic side, thereby forming the *Ein state. Thereafter, an extracellular chloride ion can be translocated and the occluded sodium ion released to the cytoplasm, which returns the transporter to the Ein state. GABA-GABA exchange can occur in the absence of extracellular chloride, but a chloride ion must be transported to complete a forward transport cycle. In the reverse transport cycle, one cytoplasmic chloride ion binds first to the Ein state, followed by two sodium ions. One chloride ion and one sodium ion are occluded together, and thereafter the second sodium ion and GABA are occluded and translocated. The weak voltage dependence of these reactions determines the slopes of outward current-voltage relations. Experimental results that are simulated accurately include (a) all current-voltage relations, (b) all substrate dependencies described to date, (c) cis-cis and cis-trans substrate interactions, (d) charge movements in the absence of transport current, (e) dependencies of charge movement kinetics on substrate concentrations, (f) pre-steady state current transients in the presence of substrates, (g) substrate-induced capacitance changes, (h) GABA-GABA exchange, and (i) the existence of inward transport current and GABA-GABA exchange in the nominal absence of extracellular chloride.     

Study of erythrocyte dehydration using spin labels

Possibility of studying erythrocyte dehydration by ESR-spin probe is substantiated. Dehydration of erythrocytes in relation to osmolarity of sodium chloride solutions is investigated. The results are shown to agree with the data obtained by radioisotope method.     

A study of passive potassium efflux from human red blood cells using ion-specific electrodes

Summary Using ion-specific electrodes, the potassium leakage induced by ouabain in human erythrocytes can be measured continuously and precisely near physiological conditions. Upon small additions of isotonic sucrose solution to a suspension of red cells in physiological saline the passive potassium efflux increases proportionally to the chloride ratio. The same result is obtained upon addition of hypertonic sucrose solution, suggesting that neither osmolarity nor intracellular concentrations have any influence on the passive potassium efflux. The independence of the potassium efflux and osmolarity can be verified by addition of a penetrating substance like glucose to the cell suspension. Adding water or hypertonic sodium chloride solution shows that the potassium efflux increases slightly in more concentrated salt solutions. Inasmuch as it can be interpreted as a pure ionic strength effect, this result supports the hypothesis of independence of potassium efflux and intracellular concentrations. The results of this investigation together with other studies show that the passive permeability of the human red blood cell to potassium depends uniquely on the membrane potential near physiological conditions, while it depends on parameters such as pH or concentrations for large membrane potentials. This suggests that two different mechanisms of transport might be involved: one would control the permeability under normal conditions; the other would represent a leak through the route normally used by anions and become important only under extreme conditions.     

Rectale Chloridepithelien und osmoregulatorische Salzaufnahme durch den Enddarm von Zygopteren und Anisopteren Libellenlarven

The larvae of Coenagrion puella possess 3, and the larvae of Aeshna cyanea up to 486 rectal chloride epithelia which in both species are organized as transporting epithelia. Combined applications of the histochemical chloride precipitation technique, energy-dispersive micro-analysis of X-rays, autoradiography, and scintillation counting on A. cyanea revealed that the chloride epithelia adsorb chloride from the external solution. By use of radioactive sodium and chloride in hypotonic concentrations applied on normal and anus-sealed larvae it was demonstrated that the rectum of both species is the main pathway for salt uptake into the haemolymph. The stepwise increase in external osmolarity by the addition of mannitol results in a concomitant reduction of chloride uptake into the haemolymph. These results suggest that the rectal chloride epithelia are involved in hyperosmotic regulation by the absorption of salt from the external medium.     

STUDIES ON THE REGULATION OF OSMOTIC PRESSURE : I. THE EFFECT OF INCREASING CONCENTRATIONS OF GELATIN ON THE CONDUCTIVITY OF A SODIUM CHLORIDE SOLUTION.

1. In pure gelatin solutions the conductivity of the solution increases with increasing concentrations, regardless of the hydrogen ion concentration. The actual value of the specific conductivity is greater at that reaction where the degree of ionization is greater. 2. The addition of gelatin in increasing concentrations to a 0.6 per cent sodium chloride solution affects the conductivity of that solution in two ways: (a) At pH 3.3, (where gelatin is highly ionized) the conductivity increases with each added increment of gelatin. (b) At pH 5.1 and 7.4 (where gelatin is less highly ionized) the conductivity decreases with each added increment of gelatin. A similar study is being made of crystalline egg albumin.     

IONS AND THE TRANSPORT OF GAMMA-AMINOBUTYRIC ACID BY SYNAPTOSOMES

Abstract— The initial rate of uptake of [2,3-³H]gamma-aminobutyric acid by rat brain synaptosomes was studied under incubation conditions in which GABA metabolism was minimal. The presence of both sodium and potassium in the incubation medium was essential for sustained uptake. Uptake proceeded for a short period of time in the absence of potassium and then ceased. No uptake was observed when sodium chloride was completely replaced with sucrose or choline chloride. The sodium-dependence curve for GABA uptake was markedly sigmoid. The sigmoid character of the curve was not attributable to a lag phase in uptake at low sodium concentrations. Calcium strongly stimulated the initial rate of uptake at low sodium concentrations but had little effect at sodium concentrations above 100 m m and was not able to support uptake in the absence of sodium. The sigmoid character of thesodium-dependence curve was completely eliminated by 20 m m calcium ion. Magnesium and phosphate had little effect on the initial rate of GABA uptake.     

Dependence of myocardial damage on the anion composition and osmotic pressure in the extracellular fluid during "calcium paradox" in rats]

The data obtained reveal that elevation of extracellular osmolarity with sucrose during reintroduction of Ca-containing medium after 10 minutes of Ca2+ removal prevents loss of haemoglobin in a concentration-dependent mode. Reducing the extracellular osmolarity of the reperfusion medium by means of decreasing the concentration of sodium chloride and calcium chloride exacerbates the loss of haemoglobin from the cardiomyocytes. There is a close correlation between the water contents in tissues and the loss of haemoglobin during the "calcium paradox". The findings suggest dependence of the heart damage during the "calcium paradox" on anionic composition of extracellular space and activity of anionic transporters.     

Ion concentrations in oviduct and uterine fluid and blood serum during the estrous cycle in the bovine

In the bovine up to 40% of embryos die before implantation but despite the importance of ions in oviduct and uterine fluid formation and in gamete, zygote and early embryo development there is very little published information on the ion concentrations of oviduct or uterine fluid. The free anions chloride, phosphate and sulphate and the free cations sodium, calcium, magnesium and potassium were measured in oviduct fluid on days 0, 2, 4 and 6 and in uterine fluid on days 6, 8 and 14 and in corresponding blood samples. Oviduct and uterine fluids were collected in situ. Sodium was 25-fold higher than potassium and 80-fold higher than the other ions and chloride was 10-fold higher than potassium and 40-fold higher than the other ions in oviduct and uterine fluid. Phosphate, sulphate, magnesium, potassium and calcium were at lower concentrations in all fluids. Oviduct calcium and sodium were higher on day 0 than other days. The most striking uterine differences were the higher potassium and lower chloride, sodium and magnesium on day 14 than other days. There were significant positive associations between oviduct and blood chloride, sulphate, magnesium and calcium while only uterine sulphate was positively related to its blood concentration. There was no relationship between fluid secretion rate and no association between the concentrations of systemic progesterone or oestradiol and any ion in oviduct or uterine fluid. The different concentrations and associations between ions in the oviduct, uterus and blood suggest a differential regulation of ion secretion by the oviduct and uterine epithelia.