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At least 973 records · Page 54Linked to original sources
PubMed2004

Ionic permeation free energy in gramicidin: a semimicroscopic perspective.

Ion permeation through the gramicidin channel is studied using a model that circumvents two major difficulties inherent to standard simulational methods. It exploits the timescale separation between electronic and structural contributions to dielectric stabilization, accounting for the influence of electronic polarization by embedding the channel in a dielectric milieu that describes this polarization in a mean sense. The explicit mobile moieties are the ion, multipolar waters, and the carbonyls and amides of the peptide backbone. The model treats the influence of aromatic residues and the membrane dipole potential. A new electrical geometry is introduced that treats long-range electrostatics exactly and avoids problems related to periodic boundary conditions. It permits the translocating ion to make a seamless transition from nearby electrolyte to the channel interior. Other degrees of freedom (more distant bulk electrolyte and nonpolar lipid) are treated as dielectric continua. Reasonable permeation free energy profiles are obtained for potassium, rubidium, and cesium; binding wells are shallow and the central barrier is small. Estimated cationic single-channel conductances are smaller than experiment, but only by factors between 2 (rubidium) and 50 (potassium). When applied to chloride the internal barrier is large, with a corresponding miniscule single-channel conductance. The estimated relative single-channel conductances of gramicidin A, B, and C agree well with experiment.

Cesium↗
PubMed1980

Effects of alkali metal chlorides on activity levels of rats in a passive exploration test.

Rats treated with alkali metal chlorides (2 mmol/kg, injected intraperitoneally) were tested for exploratory behaviour in a situation where exploration was indicated by reduced ambulatory activity. Lithium chloride significantly reduced exploration and increased ambulation as compared to sodium chloride treated control rats. Whilst rubidium chloride had similar effects to those produced by the lithium salt, these failed to reach statistical significance. The findings are discussed in the light of two hypotheses, namely that lithium attenuates the central processing of sensory information, and that rubidium acts as a nonspecific stimulant of activity.

Alkalies↗
PubMed1981

The influence of alkali metal chlorides on environmentally-linked behavioural stereotypies in the rat.

In a series of three experiments using rats, the chlorides of lithium, rubidium and caesium were compared with sodium chloride in respect of their effects on behavioural stereotypy. Two apparatuses were used, a modified hold-board and an open field. Caesium was found to increase the occurrence of environmentally-linked behaviour in both types of apparatus. Lithium had effects in the opposite direction. Rubidium had effects like caesium in the modified hold-board test, but like lithium in the open field. The findings are discussed in terms of possible effects on central information processing mechanisms.

Analysis of Variance↗
PubMed1993

Effect of metabolic inhibitors and anaerobiosis on rat lens.

The effect of the inhibitors of aerobic metabolism on the transport of rubidium and ATP content in rat lens has been studied under organ culture system. The inhibitors used were malonate, monofluoroacetate, cyanide, antimycin A, 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), 2,4-dinitrophenol (DNP) and dicumarol. All these compounds inhibited the transport of rubidium, reflecting a decrease in the ability of the lens to transport potassium. The levels of ATP also decreased. The results were similar to those obtained under anaerobic conditions where the lenses were incubated in a nitrogen atmosphere without the inhibitors. The degree of inhibition observed by the metabolic inhibitors as well as by anaerobiosis indicate that the rat lens depends substantially on aerobic oxidation for its energy needs, unlike bovine and rabbit lenses studied before.

Adenosine Triphosphate↗
PubMed1995

Effect of smoke condensate on the physiological integrity and morphology of organ cultured rat lenses.

Smoke, either from cigarette smoking or from burning of organic fuels, has been proposed to be a major environmental risk factor for a variety of human diseases. Recently, smoke was implicated in cataract, an eye lens opacification which is a major cause of blindness. We have undertaken a study to investigate the effect of wood smoke condensate on the physiological integrity and morphology of organ cultured lenses. Lenses in organ culture are metabolically active and have functional defense systems, thus they provide an appropriate model for studying effects of smoke condensate. Our present study indicates that metabolites of wood smoke condensate accumulate in the lens. The ability of the lenses to accumulate rubidium-86 (mimic of potassium) and choline from the medium is compromised by exposure to smoke condensate. Rubidium efflux studies suggest that the damage is primarily at the uptake level and does not involve an overall increase in membrane permeability. Protein leakage experiments corroborate this suggestion. Histological data show distinct morphological changes such as hyperplasia, hypertrophy and multilayering of epithelial cells.

Animals↗
PubMed1988

Peroxide damage to the eye lens in vitro prevention by pyruvate.

The ability of pyruvate to protect the eye lens against physiological damage by hydrogen peroxide has been studied. The physiological damage was estimated in terms of a decrease in the ability of the lens to transport rubidium against an electrochemical gradient under organ culture conditions. Peroxide was either added directly to the culture medium or generated therein by incorporation of xanthine and xanthine oxidase. In both these cases, addition of pyruvate to the medium led to a greater accumulation of rubidium by the lens. The net accumulation of this cation in the presence of 1 to 5 mM pyruvate from the medium containing peroxide (0.2 to 0.45 mM) was very close to that observed in the absence of peroxide. The protective effect was thus substantial. The mechanism of the pyruvate effect has been discussed, and seems to be related to the scavenging of peroxide by pyruvate.

Animals↗
PubMed1989

Effect of acute and chronic vanadate administration on sugar transport in rat jejunum.

Vanadate is known to have an insulin-like action which stimulates sugar transport in some systems like adipocytes and muscle cells, but in other systems it inhibits sugar transport by decreasing the activity of (Na+ +K+)-ATPase. To evaluate whether these two opposing actions may influence sugar transport across the intestine, we studied the effects of acute and chronic vanadate administration on the uptake of glucose, galactose, and 3-O-methylglucose in isolated rat intestinal cells. The sugar uptake measurements were also coupled by determinations of rubidium-86 uptake as a measure of the activity of the Na-K pump. Both acute and chronic vanadate administration reduced rubidium uptake by the cells but the reduction did not uniformly influence the uptake of the three sugars in question which were stimulated by the acute exposure of the cells to vanadate. Glucose uptake was also stimulated by chronic vanadate administration, but the uptakes of galactose and 3-O-methylglucose were respectively unaffected or inhibited by chronic vanadate. The findings suggest that the effect of vanadate on sugar transport is dependent on the net difference between two actions of vanadate: (i) stimulation of a receptor site (possibly an insulin receptor site) in the intestinal cell membrane and (ii) inhibition of the Na-K pump. During acute vanadate exposure, the stimulation of the receptor site was very likely a dominant feature which overwhelms the inhibition of the pump. Chronic exposure to vanadate led, on the other hand, to only a limited degree of stimulation of the receptor site and the inhibition of the Na-K pump became evident in the uptake measurements of galactose and 3-O-methyl-glucose. Glucose uptake, however, was stimulated by chronic vanadate ingestion due, very likely, to an increase in the metabolism of this sugar which occurred only with prolonged exposure of the rat intestine to vanadate.

3-O-Methylglucose↗
PubMed1981

The half-life of 87Rb.

The half-life of 87Rb was measured by a liquid scintillation method according to the efficiency tracing method. The measuring sample of rubidium chloride was dissolved in a scintillation cocktail of Insta-gel, and the rubidium was determined by gravimetry as tetraphenylborate. The result was (5.56 +/- 0.025) x 10(10) years.

Half-Life↗
PubMed1975

A 82Sr-82Rb isotope generator for use in nuclear medicine.

An improved 82Sr-82Rb generator system, based on the complexing ion-exchange resin Chelex-100, has been developed. Columns of this material can be easily and rapidly milked, and the rubidium-strontium separation factor for a fresh generator under the experimental conditions studied was found to be greater than 10-7. Approximately 80% of the 82Rb present can be delivered in a 15-ml volume of aqueous 0.2 M NH4Cl solution. After more than 6 liters of eluant had passed through the generator, the rubidium-strontium separation factor was still observed to greater than 10-5 and no unusual strontium breakthrough behavior was seen in the system over nearly three 82Sr half-lives.

Ion Exchange Resins↗
PubMed2004

[Correlation of mercury, selenium and other elements in the tissues of fishes from the regions at different mercury exposure level].

The contents of selenium and other elements in fish liver and muscle tissues collected from mercury polluted area of Wanshan, Guizhou province of China and non-known mercury polluted one of Beijing were determined with instrumental neutron activation analysis, and that of mercury was determined with atomic fluorescence spectrometry. The correlation among the determined elements, especially between mercury and selenium, in the fish tissues were studied. For most of the elements significant difference of elemental content was found between tissues of liver and muscle, and mostly the content in liver was higher than that in muscle. It was interesting to note that the average content of mercury in Guizhou fish liver was 25-fold higher than that in Beijing one, and 5-fold higher in Guizhou fish muscle than that in Beijing one. For most of the elements no significant difference on the average content was found between the same tissues of the two areas. The molar ratio of Hg/Se increased with the increasing of Hg content at the low Hg level, but the alteration trend became gently and reached to a higher constant value (about 0.2) at the higher Hg level. Only the element of bromine and rubidium was found to have strong linear correlation between the two different tissues of liver and muscle. Though certain correlation existed among the different elements of fish tissues from the two areas, the most significant and the closest one existed between the mercury and selenium of muscle tissue of Guizhou fishes. A closer correlation was also found between them of liver tissue of Guizhou fishes. As for Beijing fish tissues, the correlation of mercury and selenium only existed in liver but no correlation of them was found in muscle. Our results confirm the fact that a certain interaction exists between mercury and selenium in organisms including fish, and it is more evident as the mercury-exposed level is higher. Some significant correlation was also observed between other elements, such as potassium and sodium, cesium and rubidium, iron and zinc, in fish tissues and it could be well explained by their similar chemical and physical properties or their different biological functions.

Animals↗
PubMed1979

Ion transport in the heart atrial tissue of young and adult guinea-pigs and albino rats.

Rubidium shifts between the extracellular fluid and cells were studied in the isolated atria of guinea-pig and albino rat hearts. In the young of both species, rubidium transport from the incubation medium to the cells was much slower than in preparations from adult animals. That implies that the efficiency of membrane mechanisms for the transport of Na+ and K+ ions in the atrial tissue increases during postnatal life. This conclusion is further confirmed by the finding that the intracellular potassium concentration in the atrial tissue of the young of both species is lower, and the intracellular sodium concentration higher, than in adult animals. Conversely, the serum potassium concentration in the young is higher, and the serum sodium concentration lower, than in adult individuals.

Animals↗
PubMed1991

Influence of family history of cryptogenic hypertension, age, sex and race on lymphocyte sodium/potassium pumps.

To determine the effects of age, sex, race, and family history of hypertension on cellular cation transport, we measured specific tritiated-ouabain binding (sodium/potassium pump number), and sodium/potassium pump-mediated rubidium-86 uptake in blood lymphocytes from 105 healthy normotensive adults, comprising 23 Chinese and 19 Indian subjects who had first-degree relatives with cryptogenic hypertension, and 40 Chinese and 23 Indian matched subjects without such history. Both Chinese and Indian subjects with family history had significantly fewer sodium/potassium pumps than control subjects. Sodium/potassium pump-mediated rubidium-86 uptake was similar in these four subject groups. Seven Indian patients with untreated cryptogenic hypertension had fewer sodium/potassium pumps than normotensive Indians without family history. Age did not affect sodium/potassium pump numbers in cells from normotensive subjects. In normotensive subjects without family history. Chinese women had more sodium/potassium pumps than Chinese men, but Indian subjects did not show this pattern. We conclude that a family history of cryptogenic hypertension is associated with fewer lymphocyte sodium/potassium pumps than normal. The reduction in cellular pump number might be only a marker, or an epiphenomenon. However, the reduction in pump number might contribute to the pathogenesis of cryptogenic hypertension if it produces sodium retention in renal tubular or peripheral vascular cells.

Adult↗
PubMed2005

[Il-2-regulated expression of Na+,K(+)-ATPase in activated human lymphocytes].

Expression of Na+,K(+)-ATPase alfal-subunit and of oubain-sensitive rubidium influxes has been investigated in human peripheral blood lymphocytes. Isolated lymphocytes were stimulated by phytogemagglutinin (PHA) or interleukin-2 (IL-2). It has been shown that during the early stage of the PHA-activation the alfal-subunit abundance in the membrane fractions of the human blood lymphocytes does not change, whereas at the late stages of Go-->G1-->S transition (16-48 h) the alfa1 protein content increases. A translation inhibitor cycloheximide was found to prevent the late increase in alfa1-subunit expression. An immunosuppressant cyclosporin A decreases both IL-2-dependent T-lymphocyte progression and alfa1-subunit abundance by 48 h of PHA-induced lymphocyte activation. In the lymphocytes pretreated by PHA in submitogenic concentration (0.8-1.0 microg/ml) exogenous IL-2 (100 U/ml) induces a proliferative response as well as alfal-protein accumulation. A decrease in alfa1-protein accumulation in the presence of specific inhibitors of separate signal transduction pathways enables us to conclude that protein kinases ERK1/2 (MAPK pathway) and JAK3 (JAK-STAT pathway) mediate the IL-2-dependent regulation of Na+,K(+)-ATPase expression during lymphocyte transition from resting stage to proliferation. A correlation between changes in ouabain-sensitive rubidium influxes and the alfal-subunit amount has been demonstrated. It is concluded that IL-2-dependent-progression of normal human lymphocytes from quiescence to proliferation is accompanied by the increase in Na+,K(+)-ATPase alfa1-subunits expression, and the enhanced transport activity of a sodium pump during the prereplicative stage is provided by the increased number of functional pump units in plasma membrane.

Cell Division↗
PubMed1990

The effect of metals on the activity of L-phenylalanine hydroxylase.

The effects of 12 metals other than iron on the native (iron-containing) L-phenylalanine Hydroxylase from rat liver have been measured. The metals were tested in vivo at 10X and 100X molar excess. The effects generally are moderate deactivation of the enzyme; mercury and copper are particularly deactivating while rubidium is slightly activating. Complete restoration of the activity to the apoenzyme can only be achieved by iron(II). However, partial restoration is achieved by aluminium, thallium and cadmium. While restoration of activity under anaerobic conditions can also be achieved by iron(III), the increase in restoration ability of other transition metals under anaerobic conditions is not great. The restoration ability of rubidium increases, surprisingly, under anaerobic conditions.

Aerobiosis↗
PubMed1990

Characterization of the (Na+ (+) K+)-ATPase from 3T3-F442A fibroblasts and adipocytes. Isozymes and insulin sensitivity.

The (Na+ + K+)-ATPase from 3T3-F442A fibroblasts and adipocytes was characterized by immunoblotting, ouabain-sensitive rubidium uptake, sodium affinity, and Northern analysis. Using an antibody that cross-reacts with all three forms of the catalytic subunit of the enzyme, it was found that only the alpha 1 isozyme was present in both fibroblasts and adipocytes. This result was confirmed using an antibody specific for the alpha 2 isoform. Additionally, the ouabain dependence of Rb+ uptake in both cell types gave KI values of 0.7-1.0 X 10(-4) M, a concentration that is characteristic for the alpha 1 isoform. For both fibroblasts and adipocytes, the dependence of rubidium uptake activity on sodium concentration was characterized by K0.5 values of 9.4 and 6.2 mM, respectively, which is also diagnostic for the alpha 1 subunit in vivo. Although in fibroblasts there was no detectable message for the alpha 2 isozyme, the 3.4-kilobase message for this isozyme was present in adipocytes; this discrepancy is discussed. The (Na+ (+) K+)-ATPase was activated in fibroblasts and adipocytes by insulin at half-maximal concentrations of 11 nM and about 100 pM, respectively. Glucose uptake was also stimulated at similar concentrations of the hormone. In fibroblasts, insulin caused an increase in sodium uptake which was not inhibited by 1 mM amiloride. From these data, the presence of an insulin-sensitive sodium channel is hypothesized.

Adipose Tissue↗
PubMed1988

[Furosemide-sensitive cation transport in frog skeletal muscle fibers].

Furosemide-inhibitable components in unidirectional cation fluxes have been identified in frog skeletal muscle. In sodium loaded muscles, placed in sodium-free rubidium lithium media, furosemide (1 mM) inhibits partially rubidium and lithium influxes as well as potassium and sodium outfluxes. The furosemide-inhibitable components were found to depend on the presence of ouabain. They were greatly diminished in sodium-free magnesium media and were present in chloride-free nitrate containing media. The dependence of furosemide-inhibitable sodium efflux on internal sodium content was also described.

Animals↗
PubMedDate not supplied

Higher plasma Na+,K+-ATPase inhibitory activity in essential hypertensive patients.

The ability of plasma to inhibit 86 rubidium uptake in rat aorta and to displace [3H]-ouabain from hog brain Na+,K+-ATPase was used as a measure of plasma Na+,K+-ATPase inhibitory activity in seven normotensive and eight hypertensive subjects. Rat aortae rings were incubated in oxygenated plasma containing 86 rubidium (2 microCi/mL) for 30 mins at 37 degrees C and uptake measured and expressed as mumol/kg wet weight/min. Plasma was extracted with a mixture of chloroform and methanol (2:1) and the extract separated by silicic acid column followed by thin layer chromatography and fractions assayed for ouabain displacement using digoxin as a standard. Total ouabain displacement was calculated as the sum of all fractions. There was a strong correlation between the two methods for total plasma Na+,K+-ATPase inhibitory activity (r = 0.761, P less than 0.01). There was a significant positive correlation between plasma Na+,K+-ATPase inhibitory activity and blood pressure in all subjects. Na+,K+-ATPase inhibitory activity was significantly higher in plasma of hypertensives by both methods (P less than 0.001). The increased Na+,K+-ATPase inhibitory activity in plasma from hypertensives was due to the nonesterified fatty acid, long chain acylcarnitine and diphosphatidylglycerol fractions.

Adult↗
PubMed1985

Effects of noradrenaline on the sodium pump of guinea pig ventricle.

The effect of noradrenaline on myocardial sodium-pump activity has been studied, using a direct measure of active ion transport via the pump; namely, the ouabain-sensitive uptake of the radioisotope and potassium analogue rubidium-86 into guinea pig ventricular tissue slices. Physiological concentrations of noradrenaline caused a dose-dependent stimulation of rubidium uptake (peak response at 2 X 10(-7) M). With higher concentrations, the uptake fell progressively. At 6 X 10(-5) M, noradrenaline uptake was lower than control. The stimulatory action is not mediated by classic adrenergic mechanisms. It was not blocked by either alpha- or beta-blockade. Indirect actions via changes in membrane permeability to sodium and potassium ions are also considered. The inhibitory effect of high concentrations of noradrenaline, however, was mediated by alpha-receptors. Stimulation of the pump by noradrenaline could stabilize cellular ion concentrations and resting membrane potential. Since the pump is electrogenic, this is one mechanism by which noradrenaline will cause shortening of action potential. This may provide an explanation for the greater Q-T shortening during exercised-induced tachycardia, compared with atrial pacing. At high concentrations, attained locally during maximal sympathetic stimulation, these advantageous effects may be lost.

Animals↗