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beta-RbSb crystallizes with the LiAs structure type. As in the alpha phase (NaP type), Sb(-) forms approximate 4(1) helical chains (2(1) crystallographic symmetry), with Sb-Sb distances of 2.838 (1) and 2.862 (1) A. In contrast to the alpha phase, the helices have different chirality.
The bis(trifluoromethanesulfonyl)imidate anion crystallizes with Rb as the title dioxane 1:2 solvate, Rb(+).CF(3)SO(2)NSO(2)CF(3)(-).2C(4)H(8)O(2), with the anion in a transoid conformation, as opposed to the cisoid form typically seen when there are significant cation-anion interactions. The Rb(I) cation is eight-coordinate, interacting with one anion in a chelating fashion and with two other anions through the remaining sulfonyl O atoms. The latter interactions link ion pairs through the formation of Rb(2)O(2) dimers about inversion centers at (0, 1/2, 0) and (1/2, 1/2, 0), forming extended columns which run parallel to the a axis of the unit cell. Rb-dioxane bridges crosslink these salt columns in the (010), (001) and (011) directions, resulting in a three-dimensional network solid. One dioxane solvent molecule is disordered over two half-occupancy sites.
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Effects of secretagogues and anti-secretagogues of ACTH secretion on K+ permeability in the clonal pituitary cell line AtT-20 were measured by recording 86Rb or 42K efflux. Efflux was accelerated by the secretagogues K+, corticotrophin, forskolin, isoprenaline, and the Ca-ionophore A23187. Efflux was reduced by the inhibitors somatostatin, muscarine, and oxotremorine, or by removing external Ca. Efflux was also reduced by the K+-channel blocking compound d-tubocurarine but not by tetraethylammonium. Muscarine, oxotremorine, somatostatin, and 0 Ca2+ also reduced intracellular Ca2+ measured by quin-2 fluorescence. It is suggested that most of the resting 86Rb or 42K efflux measured under these conditions occurs via tubocurarine-sensitive Ca2+-dependent K+-channels, and that changes in efflux rate produced by secretagogues or anti-secretagogues are secondary to changes in intracellular Ca2+.
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An investigation is reported of coherent resonance in the degenerate two-level system of the (Fg = 2 --> Fe = 1) transition of the 87Rb D1 line by means of a Hanle effect configuration. In a coherent population trapping experiment, a very narrow (approximately 1-kHz) resonance superimposed upon a broader resonance (approximately 100 kHz) was observed. The dependence of the width and the amplitude of the coherent resonance on the laser power density, on additional constant magnetic fields, on the laser frequency position along the fluorescence profile, and on Rb cells with different dimensions was investigated.
We report the generation of a continuous-wave squeezed vacuum resonant on the Rb D1 line (795 nm) using periodically poled KTiOPO4 (PPKTP) crystals. With a frequency doubler and an optical parametric oscillator based on PPKTP crystals, we observed a squeezing level of -2.75+/-0.14 dB and an antisqueezing level of +7.00+/-0.13 dB. This system could be utilized for demonstrating storage and retrieval of the squeezed vacuum, which is important for the ultraprecise measurement of atomic spins as well as quantum information processing.
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We have used 87Rb nuclear magnetic resonance spectroscopy (NMR) to study in vivo rubidium kinetics in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls, using rubidium as a marker for potassium. We gave 15 male, 13-week-old SHR, mean +/- s.d. blood pressure 180 +/- 10 mmHg, and 15 age-matched normotensive controls, mean blood pressure 120 +/- 9 mmHg, a daily dose of RbCl (2 mmol/kg intraperitoneally). We made repeated NMR measurements of skeletal muscle rubidium concentrations until steady state was reached. We then withdrew rubidium and made further measurements of rubidium concentrations, at intervals, for up to 1 week after the last injection. We also measured plasma and erythrocyte rubidium concentrations by flame atomic absorption spectroscopy at similar intervals after the withdrawal of rubidium. Rubidium concentrations rose at a faster rate in SHR skeletal muscle, but the steady-state muscle rubidium concentration was the same (45 mmol/l) in both SHR and WKY rats. There was also a threefold increase in the rate of rubidium efflux from both muscle and erythrocytes in SHR. These results are consistent with a marked increase in Na+,K(+)-ATPase activity and an increase in the rate of rubidium efflux in vivo in SHR. The increased rate of rubidium efflux in SHR could represent increased K+ efflux via calcium-activated K+ channels and/or result as part of cell volume regulation secondary to increased Na(+)-H+ antiporter activity.
Digestion of renal Na/K-ATPase with trypsin, in the presence of rubidium and absence of calcium ions, produces so-called "19-kDa membranes," containing a C-terminal 19-kDa and smaller fragments (8-12 kDa) of the alpha chain, and a beta chain either intact or split into two fragments (Karlish, S. J. D., Goldshleger, R., and Stein, W.D. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 4566-4570). Cation occlusion is intact. The cation sites are thought to be located within trans-membrane segments, but the identity and number of segments involved is unknown. Analysis of Ca(2+)-induced sensitization of 19-kDa membranes to proteolysis, and characterization of the limit membrane-embedded fragments, has provided some insight into this question. Calcium ions have been shown to compete with two rubidium ions for occlusion sites on 19-kDa membranes, with a high affinity (KD approximately 2.8 microM, pH 7.5, 20 degrees C). The kinetics of displacement of rubidium by calcium ions indicate that competition is direct and is not an allosteric antagonism. At 37 degrees C, reversible displacement of rubidium ions by calcium ions is followed by an irreversible thermal inactivation of rubidium occlusion. Calcium ions partially protect rubidium occlusion sites against modification by the carboxyl reagent, N,N'-dicyclohexylcarbodiimide. We propose that calcium ions, like rubidium ions, recognize carboxyl groups at the entrance to the cation sites, but the calcium ions do not become occluded and thus fail to protect 19-kDa membranes against further proteolysis or thermal inactivation. Upon displacement of occluded rubidium, trypsin digests the Ca(2+)-bound and thermally inactivated 19-kDa membranes, and all of the membrane-embedded fragments are truncated or are split in these conditions. A related finding is that the C-terminal sequence of the 19-kDa fragment (and alpha chain), E-T-Y-Y, is digested by carboxypeptidase Y only when the rubidium occlusion is inactivated. Identification of the limit tryptic fragments indicates that polypeptide loops and the C-terminal tail of the 19-kDa fragment, N and C termini of the smaller fragments of the alpha chain, and both N and C termini of a 16-kDa fragment of the beta chain are split by proteolytic enzymes upon displacement of occluded rubidium.4+ We conclude that all fragments of 19-kDa membranes form a complex, which is stabilized and protected against proteolytic enzymes upon occlusion of rubidium ions, and which relaxes upon displacement of occluded rubidium. The cation occlusion "cage" presumably consists of litigating groups from several trans-membrane segments.(ABSTRACT TRUNCATED AT 400 WORDS)
1. We have measured the effect of oral salbutamol on cation transport in vivo by studying the disposition of an oral load of rubidium chloride in healthy treated volunteers and in untreated matched controls. 2. During the administration of salbutamol there was a significantly lower plasma rubidium concentration 5 h after the administration of the oral load of rubidium chloride, reflecting an increase in the net clearance of rubidium from the plasma into at least some tissues in vivo. 3. There was no difference in either intraerythrocytic rubidium concentrations or the pseudo-rate constant for erythrocyte rubidium uptake in vivo after salbutamol. 4. Ex vivo incubation of whole blood preloaded in vivo with rubidium showed that the clearance of rubidium from the plasma was inhibited by 95% in the presence of the Na+,K(+)-ATPase inhibitor digoxin. 5. These data suggest that salbutamol stimulates cation transport via Na+,K(+)-ATPase in vivo into some tissues but not into the erythrocyte. 6. This pattern of change in rubidium disposition after salbutamol is completely different from the patterns of change we have seen in patients with essential hypertension or acute manic illness. We therefore suggest that the changes in erythrocyte rubidium uptake which we have previously described in vivo in patients with essential hypertension or acute manic illness do not result from beta 2-adrenoceptor-mediated catecholamine stimulation of Na+,K(+)-ATPase.
The effects of 0.3-10 nM extracellular protons (pH 9.5-8.0) on ouabain-sensitive rubidium influx were determined in 4,4'-diisocyanostilbene-2, 2'-disulfonate (DIDS)-treated human and rat erythrocytes. This treatment clamps the intracellular H. We found that rubidium binds much better to the protonated pump than the unprotonated pump; 13-fold better in rat and 34-fold better in human erythrocytes. This clearly shows that protons are not competing with rubidium in this proton concentration range. Bretylium and tetrapropylammonium also bind much better to the protonated pump than the unprotonated pump in human erythrocytes and in this sense they are potassium-like ions. In contrast, guanidinium and sodium bind about equally well to protonated and unprotonated pump in human red cells. In rat red cells, protons actually make sodium bind less well (about sevenfold). Thus, protons have substantially different effects on the binding of rubidium and sodium. The effect of protons on ouabain binding in rat red cells was intermediate between the effects of protons on rubidium binding and on sodium binding. Remarkably, all four cationic inhibitors (bretylium, guanidinium, sodium, and tetrapropylammonium) had similar apparent inhibitory constants for the unprotonated pump ( approximately 5-10 mM). The K(d) for proton binding to the human pump, with the empty transport site facing extracellularly is 13 nM, whereas the extracellular transport site loaded with sodium is 9.5 nM, and with rubidium is 0.38 nM. In rat red cells there is also a substantial difference in the K(d) for proton binding to the sodium-loaded pump (14.5 nM) and the rubidium-loaded pump (0.158 nM). These data suggest that important rearrangements occur at the extracellular pump surface as the pump moves between conformations in which the outward facing transport site has sodium bound, is empty, or has rubidium bound and that guanidinium is sodium-like and bretylium and tetrapropylammonium are rubidium-like.
Leucite (KAlSi2O6) is used as a reinforcing agent in some porcelains for all-ceramic restorations; however, it increases their coefficients of thermal expansion, imposing constraints on the processing of the material. The potassium ions in leucite are exchangeable for rubidium or cesium ions, leading to rubidium leucite or cesium leucite (pollucite). Both rubidium leucite and pollucite exhibit a lower coefficient of thermal expansion and inversion temperature than leucite. The purpose of this study was to evaluate the effects of rubidium and cesium leucites on thermal expansion, microstructure, crack deflection patterns, and flexural strength of a leucite-reinforced porcelain. A dental porcelain powder was mixed with rubidium or cesium nitrate and heat-treated. Porcelain bars (n = 3) and discs (n = 15) were made with the exchanged powders. X-ray diffraction analyses were performed before and after bars were fired. Controls were made of untreated Optec HSP porcelain powder, formed into bars and disks, and baked following manufacturer's recommendations. The density of all specimens was determined by Archimedes' method. The thermal expansion behavior of the materials was measured by dilatometry. The microstructure and Vickers indentation crack patterns were investigated by scanning electron microscopy. X-ray diffraction showed that after ion-exchange and firing, leucite transformed into either tetragonal rubidium leucite or cubic cesium leucite. The mean coefficient of thermal contraction (550 to 50 degrees C) was significantly (p < 0.003) greater for the control material, followed by the rubidium-exchanged material, and lowest for the cesium-exchanged material. Crack pattern analyses revealed that the cesium-exchanged material exhibited a significantly lower number of crack deflections compared with those in the two other materials (p < 0.001). The microstructure of the two exchanged porcelain materials was dense, with well-dispersed small crystals as well as larger rubidium or cesium leucite crystals. The mean flexural strength of the rubidium-exchanged material was significantly higher than those of the other materials, which were not significantly different. It was concluded that the thermal expansion of leucite-reinforced porcelain can be lowered by ion-exchange, which also modifies the microstructure, crack deflection patterns, and flexural strength of the material.
To study the short-term uptake of potassium across the basolateral membrane into individual tubule cells, rubidium was used and measured by electron microprobe analysis. Changes of rubidium uptake were interpreted to reflect altered sodium entry and basolateral Na-K-ATPase activity. The effects of hydrochlorothiazide, amiloride and furosemide were determined in saline-loaded animals. Hydrochlorothiazide inhibited rubidium uptake in proximal convoluted and distal convoluted tubule cells. The effect was largest in distal convoluted tubule cells. Amiloride reduced rubidium uptake in principal cells as well as in proximal convoluted, distal convoluted and connecting tubule cells. Furosemide depressed rubidium uptake in distal convoluted tubule cells, but increased uptake in principal cells. Rubidium uptake into intercalated cells was not affected by any of the diuretics used. Hydrochlorothiazide and amiloride altered rubidium uptake also in cells not associated with the main diuretic action. These effects of hydrochlorothiazide and amiloride may be due to interference with cell transport mechanisms of Na-H and anion exchange.