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PubMed1982

Potassium transport across the frog retinal pigment epithelium.

Previous experiments indicate that the apical membrane of the frog retinal pigment epithelium contains electrogenic Na:K pumps. In the present experiments net potassium and rubidium transport across the epithelium was measured as a function of extracellular potassium (rubidium) concentration, [K]0 ( [Rb]0). The net rate of retina-to-choroid 42K(86Rb) transport increased monotonically as [K]0 ( [Rb]0) increased from approximately 0.2 to 5 mM on both sides of the tissue or on the apical (neural retinal) side of the tissue. No further increase was observed when [K]0 ( [Rb]0) was elevated to 10 mM. Net sodium transport was also stimulated by elevating [K]0. The net K transport was completely inhibited by 10-4 M ouabain in the solution bathing the apical membrane. Ouabain inhibited the unidirectional K flux in the direction of net flux but had no effect on the back-flux in the choroid-to-retina direction. The magnitude of the ouabain-inhibitable 42K(86Rb) flux increased with [K]0 ( [Rb]0). These results show that the apical membrane Na:K pumps play an important role in the net active transport of potassium (rubidium) across the epithelium. The [K]0 changes that modulate potassium transport coincide with the light-induced [K]0 changes that occur in the extracellular space separating the photoreceptors and the apical membrane of the pigment epithelium.

Animals↗

PubMed1986

The effect of cholesterol on glycerophosphono- and glycerophosphinocholines. Permeability measurements in lipid vesicles.

The kinetics of spontaneous chloride ion efflux and valinomycin-mediated rubidium-86 efflux from vesicles prepared from synthetic phospholipids with carbon-phosphorus linkages were investigated at temperatures above the gel-to-liquid-crystalline phase transition. The rate constants for the movement of chloride and rubidium ions were reduced by incorporation of cholesterol into bilayers of phosphono- and phosphinocholines. Nonisosteric phosphonolipids in which the oxygen was removed from the glycerol side of phosphorus without substitution by a methylene group interacted less with cholesterol than the analogous isosteric derivatives, as judged from the magnitude of the decrease in the rate constants for chloride and rubidium ion efflux. The experiments reported in this study suggest that steric factors in the glycerol side of the phosphorus function are important in phosphatidylcholine-cholesterol interaction. However, the oxygen atom on the choline side of the phosphorus in the phosphatidylcholine molecule is not required for strong phosphatidylcholine-cholesterol interaction, since isosteric glycerophosphinocholines interacted as well as the corresponding isosteric glycerophosphonocholines. Furthermore, steric requirements on the choline side of phosphorus are not important in this interaction since phosphinates whose head-group structures are -P(O-)CH2CH2N+(CH3)3 and -P(O-)CH2CH2CH2N+(CH3)3 interacted equally well with cholesterol, as estimated by these permeability studies.

Chlorides↗

PubMed1987

Specificity of action of the novel antihypertensive agent, BRL 34915, as a potassium channel activator. Comparison with nicorandil.

Experiments have been performed to investigate the specificity of the mechanism of action of the novel antihypertensive agent, BRL 34915. BRL 34915 (0.5-100 microM) and nicorandil (10-500 microM) stimulated the efflux of rubidium from preloaded rabbit isolated mesenteric arteries. BRL 34915 also caused an increase in the rubidium efflux rate constant in other vascular smooth muscles. Tetraethylammonium (0.1-30 mM) inhibited BRL 34915 (10 microM), nicorandil (100 microM) and potassium (30 mM) induced stimulations of rubidium efflux, but had no effect on noradrenaline (30 microM) induced efflux. Only noradrenaline induced efflux was inhibited by apamin (3-100 nM). Examination of other second messenger systems demonstrated that BRL 34915 (at concentrations up to 100 microM) did not have any appreciable effect on cGMP accumulation in rabbit mesenteric artery, cAMP or cGMP phosphodiesterase in rat heart, or cAMP and inositol phosphate accumulation in rat brain slices. Nicorandil (100 microM) caused a small increase in cGMP accumulation in rabbit mesenteric artery. Radioligand binding studies showed that BRL 34915 did not interact with dihydropyridine, 5-hydroxytryptamine, dopamine, alpha 1, alpha 2 or beta adrenoceptor binding sites. [3H]-BRL 34915 did not bind specifically to any site in any tissue studied, either in vitro or ex vivo. Thus we have been unable to demonstrate an effect of BRL 34915 other than of increasing potassium efflux in rabbit vascular smooth muscle. This lends support to other evidence suggesting that BRL 34915 relaxes vascular smooth muscle (and hence lowers blood pressure) by a novel, and specific, mechanism involving hyperpolarisation of the smooth muscle cell membrane.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1988

Alteration of multiple cell membrane functions in L-6 myoblasts by T-2 toxin: an important mechanism of action.

Recent studies suggest that T-2 toxin interacts with cell membranes and alters membrane function. This study was done to assess the effect of T-2 toxin on a broad range of cell membrane functions in L-6 myoblasts. The following parameters were assessed after exposure to T-2 toxin for 10 min: (1) the uptake of calcium, rubidium, and glucose; (2) the uptake of leucine and tyrosine and incorporation into protein; (3) the uptake of thymidine and incorporation into DNA; and (4) residual cellular lactate dehydrogenase (LDH) as a measure of cell membrane integrity. The effects of T-2 toxin on these parameters were: (1) The minimal effective concentration (MEC) of T-2 toxin that caused a reduction in the uptake of calcium and glucose was 4 pg/ml. The uptake of rubidium was increased at 0.4 pg/ml and then reduced at 4 pg/ml and higher concentrations. (2) The MEC for reduction of the uptake of leucine and tyrosine and their incorporation into protein was 4 pg/ml. (3) Thymidine uptake and incorporation into DNA showed a biphasic response with an increase at 0.4 pg/ml and a reduction at 4 pg for uptake and 40 pg/ml for incorporation. (4) Intracellular LDH was reduced at 4 ng/ml. (5) Calcium efflux was reduced after 1-, 5-, and 15-min exposures to T-2 toxin in a concentration of 40 ng/ml. All of the changes noted, including protein synthesis inhibition, were present to a significant degree within 10 min of exposure to T-2 toxin. This time interval is too short to attribute all of these effects directly to protein synthesis inhibition since most short-lived proteins have half-lives measured in hours. In conclusion, T-2 toxin appears to have multiple effects on cell membrane function at very low concentrations (0.4 pg/ml to 4 ng/ml), which are independent of protein synthesis inhibition. These likely include effects either direct or indirect on amino acid, nucleotide, and glucose transporters, as well as calcium and potassium (rubidium) channel activities.

Calcium↗

PubMed1984

Chronotropic effect of alkali metals on spontaneously beating right atria.

The alkali metal ions lithium, potassium, rubidium and cesium depress the rate of spontaneous beating of isolated rabbit right atria. At low concentrations (2 to 4 mM) the negative chronotropic effect was in the order: Cs greater than Rb greater than K or Li; at a higher concentration (12 mM) it was Rb or K greater than Cs or Li. Force of contraction was also depressed by potassium and cesium at all levels, but was stimulated by lithium and by low levels of rubidium (2 mM). Lithium had little chronotropic effect up to relatively high concentrations, decreasing spontaneous beating rate to 80% of control at 100 mM LiCl. The significant positive inotropic effect at 2 mM LiCl (to 120% of control) increased (to 180% of control) at 40 mM LiCl. Rate of beating was significantly depressed by 0.2 mM CsCl. The chronotropic effect of cesium was biphasic; the decrease in SBR at 2 and 4 mM cesium was greater than the negative chronotropic effect at 10 mM CsCl. The effect of rubidium (above 4 mM) closely resembled that of increased potassium in decreasing spontaneous beating rate and contractile force.

Animals↗

PubMed2006

Activation of the Escherichia coli cell division protein FtsZ by a low-affinity interaction with monovalent cations.

We have investigated the activation of FtsZ by monovalent cations. FtsZ polymerization was dependent on the concentrations of protein and monovalent salts, and was accompanied by the uptake of a single ion per monomer added. The affinity and the specificity for the cation were low. Potassium, ammonium, rubidium or sodium activated FtsZ to different extents. Electron microscopy showed that polymers formed with either rubidium, or potassium, were very similar, as were their nucleotide turnover rates. The GTPase activity was lower with rubidium than with potassium, indicating that nucleotide exchange is independent of nucleotide hydrolysis. Control of polymerization by binding of a low affinity cation might govern the dynamic behavior of the FtsZ polymers.

Cations, Monovalent↗

PubMed1977

The effect of ouabain on nutritional circulation and regional myocardial blood flow.

The effect of ouabain on myocardial nutritional circulation (rubidium-86 extraction) and regional myocardial blood flow (radioactive microspheres) was studied in the isolated supported canine heart preparation perfused at a constant coronary blood flow. Ouanbain (25 mug per kilogram, intravenously) produced a significant increase in mycocardial contractile force, peak left ventricular systolic pressure, and myocardial oxygen consumption. Ouabain also decreased rubidium-86 extraction (E86RB), rubidium-86 clearance (C86Rb), and the capillary transport coefficient (PS). Intracoronary infusion of ouabain (10 mug per minute) produced significant increases in contractile force (25,50, and 100 per cent above control), left ventricular systolic pressure, myocardial oxgen consumption, and the epicardial-endocardial blood flow ratio (epi/endo) of the left ventricle. When left ventricular systolic pressure was held constant (100 mm. Hg), ouabain infusion (10 mug per minute, intracoronary) increased myocardial contractile force (25,50, and 100 per cent above control) and myocardial oxygen consumption but did not change the epi/endo of the left ventricle. These results suggest that ouabain reduces E86Rb, C86Rb, and PS by producing a shunting of blood flow from endocardium to epicardium in the left ventricle. The increase in left ventricular systolic pressure appears to be responsible for these changes.

Angina Pectoris↗

PubMed1958

Potassium-dependent sodium extrusion by cells of Porphyra perforata, a red marine alga.

Potassium-free artificial sea water causes a loss of cell potassium and a gain of cell sodium in Porphyra perforata, which is not attributable to an inhibition of respiration. On adding KCl or RbCl to such low potassium, high sodium tissues, net accumulation of potassium or rubidium takes place, accompanied by net extrusion of sodium. Rates of potassium or rubidium accumulation and sodium extrusion are proportional to the amount of KCl or RbCl added only at low concentrations. Saturation of rates is evident at KCl or RbCl concentrations above 20-30 mM, suggesting the role of an ion carrier mechanism of transport. Evidence for and against mutually dependent sodium extrusion and potassium or rubidium accumulation is discussed.

Eukaryota↗

PubMed1976

Composition of bladder stones in Rwanda.

A small area of endemic bladder stone formation occurs in Rwanda, Central Africa. The X-ray diffraction of 13 of these stones revealed that they were mainly composed of calcium oxalate monohydrate. By X-ray fluorescence the presence of considerable amounts of rubidium was demonstrated which was measured by atomic absorption spectrometry. The concentration of rubidium was about 2-5 times greater than that of zinc. Thy hypothesis that rubidium is an important lithogenic element is formulated. It might explain this endemic bladder stone formation which is exceptional for Central Africa.

Adolescent↗

PubMed1976

Further evidence that prostaglandins inhibit the release of noradrenaline from adrenergic nerve terminals by restriction of availability of calcium.

1 Guinea-pig vasa deferentia were continuously superfused after labelling the transmitter stores with [3H](-)-noradrenaline. Release of [3H]-(-)-noradrenaline was induced by transmural nerve stimulation. 2 Prostglandin E2 (14 nM) drastically reduced the release of [3H]-(-)-noradrenaline, while tetraethylammonium (2 mM), rubidium (6 mM), phenoxybenzamine (3 muM) each in the presence or absence of Uptake 1 or 2 blockade, and prolonged pulse duration (from 0.5 to 2.0 ms) all significantly increased the release of [3H]-(-)-noradrenaline per nerve impulse. 3 The inhibitory effect of prostaglandin E2 on evoked release of [3H]-(-)-noradrenaline was significantly reduced by tetraethylammonium, rubidium and prolonged pulse duration, whilst it was actually enhanced by phenoxybenzamine. This indicates that increased release of noradrenaline per nerve impulse does not per se counteract the inhibitory effect of prostaglandin E2. 4 It is concluded that tetraethylammonium, rubidium and prolonged pulse duration counteracted the inhibitory effect of prostaglandin E2 on T3H]-(-)-noradrenaline release by promoting calcium influx during the nerve action potential. The results are consistent with, and add more weight to the view that prostaglandins inhibit the release of noradrenaline by restriction of calcium availability.

Action Potentials↗

PubMed1987

Membrane conductance and potassium permeability of the rat lens.

The membrane potential, electrical impedance and 86Rb+ efflux rate constants were measured in the rat lens perifused at 35 degrees C. The membrane conductance was obtained from the difference between the magnitude of the impedance at low (less than 0.1 Hz) and high (greater than 100 Hz) frequencies. Values of the rubidium permeability coefficients (PRb) were obtained from the rate constant and potential data. The values for the membrane potential and conductance in control solution (5 mM potassium) were -69.6 mV and 5.5 X 10(-4) S respectively, while the computed permeability was 2.9 X 10(-8) m.s-1. On perifusing with 35 mM potassium, the membrane depolarized by 25 mV and the conductance and rubidium permeability increased considerably. These increases could be blocked by quinine (0.3 mM), tetraethylammonium (30 mM) and 4-aminopyridine (10 mM). The latter agent was more effective at alkaline pH (8.3). It is suggested that there are voltage-gated potassium channels that are inhibited by these three agents. After the initial depolarization in high potassium, there was little further change in membrane potential with any of the inhibitors. All three agents, however, produced a marked depolarization when applied in control solution. This was accompanied by a decrease in conductance and rubidium permeability, suggesting that, in the rat lens, some voltage-gated potassium channels are activated at the resting potential.

4-Aminopyridine↗

PubMed1972

Efflux of potassium from the isolated frog retina: a study of the photic effect.

1. Illumination of the isolated frog retina reduces the efflux of (42)K (and (86)Rb).2. Perfusion with a solution containing glutamate ions does not abolish the effect, although the electroretinogram is modified and the b-wave absent in this condition.3. Perfusion with a solution with only 2.36 mM sodium abolishes the effect of light on the efflux of potassium (and rubidium).4. The amplitude of the photic effect, measured in the first 2 min of illumination, is in linear proportion with the logarithm of the concentration of extracellular sodium ions.5. A steady rate of absorption of a few quanta per rod and per second yields a just detectable effect on the efflux of potassium (and rubidium).6. Strong illuminations followed by darkness reduce the efflux of rubidium for a period of time roughly comparable to the time of dark adaptation.7. The interpretation is proposed that the photoreceptor cells (and possibly other retinal cells too) cause the effect, and that the retention of potassium induced by light is secondary to the hyperpolarization of their membrane.

Animals↗

PubMed1974

Characteristics of streptolysin O hemolysis: kinetics of hemoglobin and 86rubidium release.

The characteristics of hemolysis produced by streptolysin O (SLO) were investigated in rabbit, human, and rat erythrocytes. Kinetic studies of hemoglobin (Hb) release showed that rabbit and human erythrocytes exhibited typical "multi-hit" survival curves. Extrapolation of these curves to the ordinate indicated that approximately two molecules of SLO may be sufficient to produce lysis of a single cell. In contrast, exponential ("single-hit") survival curves were observed when rat erythrocytes were treated with SLO. At 0 C, high concentrations of SLO rapidly lysed rabbit erythrocytes; low concentrations had no effect on the cells at this temperature. The release of intracellular (86)rubidium ((86)Rb(+)) and Hb in rabbit erythrocytes exposed to SLO was investigated. In the presence of phosphate-buffered saline, rubidium and Hb were lost at the same rate from toxin-treated cells. The addition of bovine serum albumin to the suspending medium did not retard the escape of Hb, and the efflux of (86)Rb(+) only slightly preceded Hb loss. Addition of sucrose to the cells delayed both Hb and rubidium release. These results are interpreted as indicating that the "colloid-osmotic" lytic process is not involved in the hemolysis of erythrocytes by streptolysin O.

Animals↗

PubMed1993

Enhanced chemical strengthening of feldspathic dental porcelain.

Previous studies on ion exchange of dental ceramics have shown that the biaxial flexural strength can be improved by exchanging potassium for sodium ions at temperatures below the strain point. The rubidium ion is bigger than the potassium ion and can also be considered as a candidate for replacing smaller ions, i.e., sodium or potassium, although it has not been used for dental ceramics. The double-step method uses the exchange of a small ion for a large ion (Li for Na) above the strain point, and the further exchange of a large ion for a small ion (K for Li) below the strain point. The purpose of this study was to compare the effect of rubidium-for-potassium ion exchange with that of potassium-for-sodium exchange (Tuf-Coat, G-C International Corp., Japan) on the flexural strength of a feldspathic dental porcelain and to test the hypothesis that a double-step ion exchange can lead to greater strengthening than potassium ion exchange alone. Weight measurements were performed before and after treatment. Qualitative chemical analyses allowed the rubidium, potassium, and sodium concentration profiles to be determined along cross-sections of the specimens. The maximum biaxial stresses were calculated after specimens were fractured in water on a ball-on-ring fixture at 0.5 mm/min. Relative to the untreated control group, the flexural strength of the potassium-exchanged groups was significantly increased, except for those treated at 400 or 500 degrees C. All the groups treated with RbNO3 exhibited a significant increase in flexural strength, with a maximum for the group treated at 450 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Silicates↗

PubMed1989

The effect of lithium on cation transport measured in vivo in patients suffering from bipolar affective illness.

We have investigated cation transport in vivo in patients being treated with lithium for bipolar affective illness by studying the disposition of rubidium after an oral load of rubidium chloride. The rate of erythrocyte cation transport was increased in the patients when compared with matched healthy volunteers. However, the rate of in-vivo erythrocyte rubidium accumulation in the euthymic treated patients was significantly lower than in a matched group of unmedicated manic patients. The regulation of specific pathways for cation transport may be altered in individuals predisposed to affective illness.

Adult↗

PubMed1976

Subcellular localization of diffusible ions in the yeast Saccharomyces cerevisiae: quantitative microprobe analysis of thin freeze-dried sections.

In yeast cells, of which the intracellular potassium had been partly replaced by rubidium or caesium, the intracellular ion distribution was studied by means of energy-dispersive X-ray microanalysis. The cells were rapidly frozen and thin sections were cut at low temperature on a cryo-ultramicrotome without the use of a trough liquid. By this dry cryosectioning procedure, complete retention of the diffusbile ions in the cells was obtained. Unless the sections had been exposed to moisture, no signs of redistribution were apparent. For quantitative determinations a gelatin standard, containing known amounts of the elements of interest, was prepared in the same way as the cells. The concentrations of potassium, rubidium, caesium and chloride in the nucleus, the cytoplasm and the vacuole could be measured. The intracellular distributions of potassium, rubidium and caesium were very similar. The concentrations of these ions in the cytoplasm were about equal to those in the nucleus and twice those in the vacuole. The total concentration in the cytoplasm was 180-190 mmol/kg fresh weight, in the nucleus 190-200 mmol/kg fresh weight and in the vacuole 75-90 mmol/kg fresh weight. The permeability of the yeast cell for chloride is markedly lower than for the cations.

Cell Nucleus↗

PubMedDate not supplied

[Properties of artificial vesicles from biological membranes].

Ultrasonic treatment of microsome fraction or the preparation of partially purified Na+, K+-ATPase from cattle brain resulted in the formation of closed structures which immobilized rubidium and sodium ions and were easily discovered in electron microscope. Gradual release of bound rubidium ions was observed under the incubation of ultrasonic-treated membrane preparation in salt solutions. This process was activated by ATP. ATP-activated release of rubidium was observed only in the presence of sodium and was inhibited by ouabain. A hypothesis on the participation of sodium pump in the ion transport through membranes of artificial vesicles is discussed.

Adenosine Triphosphatases↗

PubMed1985

[Dependence of ion transport across the plasma membrane on cell culture density. II. Active and passive cation transport during the growth of L cell cultures].

Rubidium and lithium influxes as well as intracellular potassium and sodium contents were investigated in L cells during the culture growth. In sparse culture over the cell densities 0.5-3 X 10(4) cells/cm2 ouabain-sensitive rubidium influx is small and ouabain-resistant lithium influx in high. With the increase in culture density up to 4-5 X 10(4) cells/cm2 the active rubidium influx, mediated by ouabain-sensitive component, is enhanced, and ion "leakage" tested by lithium influx is diminished. Simultaneously with the exponential growth of culture the intracellular potassium content is increased and the intracellular sodium content is decreased resulting in the higher K/Na ratio in cell. During the further transition to dense culture and in stationary state (10-17 X 10(4) cells/cm2) the sodium content and lithium influx do not change significantly, but the potassium content is decreased. The decrease in intracellular potassium is correlated with that in the portion of cells in S-phase from 27-30 to 12%. Thus, in transformed cells the density-dependent alterations in membrane cation transport are observed.

Animals↗