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PubMed1990

Thallium and rubidium permeability of human and rat erythrocyte membrane.

Transport of Tl+ and Rb+ in human and rat erythrocytes was investigated in the presence of ouabain. The chloride-dependent cotransport of Tl+, Rb+ and Na+ was precluded by replacement of Cl- by NO3-. The inward and outward rate constants for the residual fluxes of the cations were determined by measuring the transport of 204Tl and 86Rb in double label experiments. The rate of passive transport of Tl+ exceeded that of Rb+ by one-two orders of magnitude in human as well as rat erythrocytes. The membrane barrier which contributes to the maintenance of ion gradients was shown not to be a barrier for Tl+ which easily penetrates the membrane by an unknown mechanism. In rat erythrocytes the barrier for Rb+ was 10-15 times weaker than that in human red blood cells, while the corresponding ratio of rat/human Tl+ permeabilities was about 1.8-2.0. It follows that Tl+ permeability is only slightly affected by factors modifying the permeability to alkali cations. The increase of temperature from 20 degrees to 37 degrees C resulted in a three-fourfold stimulation of the passive transport of Tl+ both in human and rat erythrocytes. The movement of Tl+ and Rb+ through the erythrocyte membrane differed substantially from their diffusion along the excitable membrane channels characterized both by poor Tl+/K+ selectivity and weak temperature dependence.

Animals↗
PubMed1993

Rubidium occlusion within tryptic peptides of the H,K-ATPase.

86Rb+ binding to the H,K-ATPase was measured in the Mg(2+)-vanadate-inhibited enzyme at 4 degrees C. The concentration dependence of 86Rb+ binding in detergent-free preparations exhibited two components, one saturable with a K0.5 (Rb+) of 0.76 +/- 0.3 mM and a binding capacity of 2626 +/- 690 pmol of Rb+/mg of protein and the second nonsaturable, but linearly dependent, upon the 86Rb+ concentration. The concentration dependence of 86Rb+ binding was unaffected by digitonin treatment with a K0.5 (Rb+) of 0.63 +/- 0.09 mM and a binding capacity of 2824 +/- 152 pmol of Rb+/mg of protein, but the amplitude of the nonsaturable component was eliminated. The level of 86Rb+ binding was optimized by vanadate and decreased by ADP and ATP, suggesting that cation binding is stabilized in the E2-like conformation and antagonized in the E1 conformation. The Rb(+)-dependent stabilization of the E2 enzyme conformation was confirmed from the fluorescent quench response of the fluorescein isothiocyanate (FITC)-labeled enzyme, where 86Rb+ bound to the FITC-labeled enzyme with a K0.5 = 0.85 +/- 0.3 mM and a saturable binding capacity of 2121 pmol of 86Rb+/mg of protein and quenched the FITC fluorescence with a K0.5(Rb+) of 3.6 +/- 0.3 mM. The K(+)-competitive inhibitor, 1-(2-methylphenyl)-4-methylamino-6-methyl-2,3-dihydropyrrolo[3,2-c ]quinoline (MDPQ), also quenched FITC fluorescence with a K0.5(MDPQ) of 24.5 +/- 0.6 microM and competitively inhibited 86Rb+ binding with a K*0.5 = 35.8 microM (MDPQ). The MDPQ-induced quench of FITC fluorescence at Lys517 within the cytoplasmic M4/M5 nucleotide domain and displacement of 86Rb+ from a functionally defined extracytoplasmic binding domain indicate that structural determinants of the E2 conformational state exist within both cytoplasmic and extracytoplasmic domains of the H,K-ATPase and thus provide evidence of concerted conformational changes between the nucleotide and cation binding domains within the FITC-labeled H,K-ATPase. Membrane-bound fragments of the H,K-ATPase were prepared by tryptic hydrolysis in KCl medium. Tryptic digestion rapidly inactivated the phosphoenzyme site with a time course where k = 0.25 +/- 0.04 min-1 but both 86Rb+ binding and MDPQ fluorescence responses were retained. The concentration dependence of 86Rb+ binding and Rb(+)-dependent MDPQ fluorescence responses in the trypsin-digested membranes were described by a single class of binding sites where K0.5 = 1.2 +/- 0.3 and 0.73 +/- 0.09 mM, respectively. The stability of the Rb+ and MDPQ sites suggest their locations are near or within the membrane and are inaccessible to trypsin attack.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed2000

Effects of ischemia on intracellular rubidium in pig and rat hearts: (87)Rb NMR imaging and spectroscopic study.

87Rb MR imaging and spectroscopy were used to study the effects of ischemia on the properties of K(+) in cardiac tissue. Isolated pig and rat hearts perfused by the Langendorff method with Krebs-Henseleit buffer were preloaded with Rb(+). Ischemia (Isc) was induced by 120-min occlusion of the left anterior descending artery in the pig hearts or by stopping perfusion for 33 min in the rat hearts. Serial (87)Rb MR images or spectra from the anterior (An) LV wall of pig hearts were acquired continuously. The intensities of the Rb images of the An and posterior (Pos) walls were similar and stable during the first 45 min of ischemia. The intensity of signal from the An wall (Isc) then gradually increased by 60 +/- 8% relative to the preischemic value (vs. 31 +/- 5% increase in Pos wall) and necrosis (19 +/- 5% of the LV wall mass) developed upon reperfusion. The Rb(+) content was lower in the ischemic (An) than in the normal (Pos) area (22.3 +/- 3 vs. 28.4 +/- 1.3 mmol/g wet wt). A similar pattern was observed in the peak heights of (87)Rb spectra from the An wall, which increased by 40 +/- 16% (vs. 21 +/- 11% in control) due to a 12% decrease in the apparent Rb linewidth (LW) and a 24 +/- 14% increase in the peak area. The Rb peak comprised narrow (297 +/- 21 Hz) and broad (1098 +/- 40 Hz, 59 +/- 3% of total area) Lorentzian components. The LW of the broad component decreased by 14%, while the narrow component did not change markedly. In the rat hearts ischemia caused a 33 +/- 4% increase in the (87)Rb peak height as a result of peak narrowing (13 +/- 1%), and an increase in peak area (17 +/- 5%). The decreases in LW and increases in Rb(+) visibility can be explained by an increase in Rb(+) mobility caused by displacement of Rb(+) from anionic binding sites by H(+) (ischemic acidosis) and changes in intracellular compartmentalization of Rb(+). Magn Reson Med 44:193-200, 2000.

Analysis of Variance↗
PubMed1990

Acute myocardial infarction associated with intravenous dipyridamole for rubidium-82 PET imaging.

This report describes the occurrence of chest pain and electrocardiographic features of acute myocardial infarction following intravenous dipyridamole-handgrip stress. Myocardial perfusion imaging (Rb-82 PET) demonstrated a stress-induced perfusion defect. Following failure to respond to medical therapy, urgent cardiac catheterization demonstrated total occlusion of the left anterior descending coronary artery. The vessel was revascularized, with limitation of myocardial damage evidenced by failure to develop anterior Q waves and only modest elevation of cardiac enzyme levels. Complications of intravenous dipyridamole stress are rare, this case constituting the first major problem in over 500 such procedures at this institution. However, this experience demonstrates the importance of vigilant observation during the performance of this technique.

Dipyridamole↗
PubMed1981

Sodium and rubidium uptake in cells transformed by Rous sarcoma virus.

Rates of uptake and intracellular concentrations of monovalent cations were measured in virus-transformed and nontransformed chick embryo (CE) cells. Uptake of 22Na+ into cells transformed by the BH strain of Rous sarcoma virus (RSV-BH) (CE-BH) was about double the rate of uptake into CE cells, or cells transformed by the Schmidt-Ruppin strain (RSV-SR): CE-SR. Likewise, the rate of efflux of 22Na+ was greater in CE-BH cells than in CE or CE-SR cells. The greater permeability of CE-BH cells to Na+ was apparent in higher intracellular Na+ concentrations. Experiments with cells exhibiting temperature-dependent transformation showed that new RNA and protein synthesis was a requirement for the acquisition of increased Na+ permeability, suggesting that the change is an indirect effect of the virus-coded transformation-inducing protein. Rates of 86Rb+ uptake, used as a measure of K+ influx, were indistinguishable in CE, CE-BH, and CE-SR cells. Also, equilibrium intracellular levels of 86Rb+ were similar in transformed and nontransformed cells, as were observed concentrations of K+. Also, no differences in ATPase activity, as indicated by ouabain binding or temperature sensitivity, were observed. We conclude that monovalent cations play no direct role in RSV-induced transformation, although the higher levels of Na+ in CE-BH cells may be responsible for other distinguishing biochemical features of these cells.

Animals↗
PubMed2005

Rubidium-87 magnetic resonance spectroscopy and imaging for analysis of mammalian K+ transport.

This review summarizes results 87Rb MRS/I studies of K+ transport in mammalian cells, organs and in vivo. It provides a brief description of K+ transport systems, their interactions with Rb+ and evidence that Rb+ is a best K+ congener. 87Rb MR studies have focused mostly on isolated perfused rat and pig hearts and to a lesser extent on kidney, skeletal muscle, salivary gland and red blood cells. The method has been used for three purposes: measurements of kinetics of unidirectional Rb+ uptake and efflux and steady-state Rb+ levels. In cardiovascular studies Rb+ has been used in the absence of shift reagent taking advantage of the predominantly intracellular Rb+/K+ distribution (approximately 20:1). Pharmacological analysis of Rb+ uptake and efflux allowed assessment of the contributions of various transporters to the total Rb+ fluxes in rat hearts. It was confirmed that Na+/K+ ATPase is responsible for the majority of K+ influx since Rb+ uptake is 80% ouabain-sensitive and dependent on the intracellular [Na+]. Energy deprivation caused by low-flow ischemia or metabolic inhibition reduced Rb+ uptake rate. Under normal conditions, Rb+ efflux is mediated mainly by voltage-gated K+ channels with a small contribution from the K+/Na+/2Cl- cotransporter. Intracellular alkalosis and osmotic swelling stimulated Rb+ efflux by activation of the putative K+/H+ antiporter. Activity of ATP-sensitive K+ (K(ATP)) channels was revealed by metabolic (2,4-dinitrophenol, ischemia) or pharmacological (K(ATP) opener, P-1075) stimulation of Rb+ efflux, which was reversed by the K(ATP) blocker, glibenclamide. Mitochondrial K+ transport was evaluated in hearts with saponin-permeabilized myocytes and under hypothermic conditions.Three-dimensional (3-D) spectroscopic MRI of isolated beating pig hearts has been used to obtain time series of Rb+ maps of normal and ischemic/infarcted hearts, which showed lower image intensity in the damaged area. Kinetics of Rb+ uptake in the ischemic areas depended on both regional flow and metabolism. The adrenergic agonist dobutamine stimulated Rb+ uptake in normal areas and did not affect uptake in ischemic areas. Drugs that may affect passive Rb+ transport (bumetanide, pinacidil, glibenclamide) did not change Rb+ uptake either in the normal or ischemic zones. 87Rb-MRI was also able to localize ischemia and infarction in blood-perfused hearts. 87Rb MRS/I is an excellent non-invasive research tool for studies of K+ transport in isolated organs and in vivo.

Animals↗
PubMed1996

Association of rubidium and C-methionine uptake in brain tumors measured by positron emission tomography.

Positron emission tomography (PET) studies have indicated that alteration of active transport contributes to increased net amino acid accumulation into human brain tumors. We compared the uptake of 11C-methionine (MET) and the K+ analog 82Rubidium (RUB) in 30 patients suffering from various brain tumors using PET. MET and RUB accumulated rapidly in tumor tissue and remained on average at a stable level thereafter from which normalized uptake values calculated (tissue radioactivity over injected radioactivity x body weight (NU). K1 (RUB) and K1, k2, k3 (MET) were also estimated using non-linear rate constant fitting in 17/30 patients. NU and K1 values for MET and RUB were higher in meningiomas compared to gliomas and were significantly correlated for the whole spectrum of tumors (p < 0.0001). When meningiomas were excluded, the correlation was maintained. K3 values for MET (metabolic rate) in tumors were in the range of normal brain. No correlation between RUB and MET was found for normal brain. with increasing rub intake the ratio of Nu MET over Nu RUB approached the value of 1.0. These results suggest that apart from active transport, also passive diffusion across the blood-brain barrier (BBB) may account for MET uptake from blood into tumor tissue. This probably limits the use of MET in the differential diagnosis of brain lesions where BBB disruption is present.

Adolescent↗
PubMed1980

Influence of the murine diabetes gene on rubidium ion efflux from perifused islets.

Islets from diabetic C57BL/KsJ db/db mice and normal C57BL/KsJ +/+ mice were loaded with 86Rb+ and micro-perfused with nonradioactive medium for 25 min. The appearance of 86Rb+ in the effluent could be described as the sum of two exponential functions with difference proportionality constants. The rapid efflux component may have represented washout from the extracellular space, and had about the same proportionality constant in normal and diabetic mice. The slow efflux component probably reflected efflux across the islet cell plasma membranes. At 3 mmol/l D-glucose in the medium, the slow efflux was significantly retarded in diabetic as compared with normal mice. In normal mice, but not in diabetics, 20 mmol/l D-glucose inhibited the slow efflux component. It is concluded that the basal K+ permeability is decreased in KsJ db/db mouse islet cells, and that this abnormality may explain their persistant depolarization at low glucose concentrations.

Animals↗
PubMed1983

Isolation and purification of plasmids from Bacteroides fragilis using rubidium trichloroacetate density gradient centrifugation.

A rapid and easy final purification method is described for the isolation of plasmids from B. fragilis. Using RbTCA density gradient centrifugation in an airfuge ultracentrifuge ccc plasmid DNA can be separated from RNA, residual chromosomal DNA, linear and oc plasmid DNA. Pure ccc plasmid DNA is obtained from cultures of between 1 ml and 2 l in less than one day.

Bacteroides fragilis↗
PubMed1990

Effect of amiloride on electrolyte concentrations and rubidium uptake in principal and mitochondria-rich cells of frog skin.

The role of mitochondria-rich cells (MR cells) in transepithelial Na transport was investigated by determining electrolyte concentrations and Rb uptake in individual cells of frog skin epithelium using electron microprobe analysis. Measurements were performed under control conditions and after blocking the transepithelial Na transport with amiloride. Under control conditions, Na and Cl concentrations of MR cells scattered much more than those of principal cells and ranged from a few up to more than 30 mmol/kg wet weight. Rb uptake from the basal side into individual MR cells also showed a large variation and was, on the average, much less pronounced than into the principal cells. In principal cells, amiloride reduced the Na concentration and Rb accumulation. In contrast, no effect was observed upon electrolyte concentration and Rb uptake of MR cells. Rb uptake was correlated to the Na concentration of MR cells both under control conditions and after amiloride. It is concluded that, in contrast to the principal cells, MR cells are not involved in amiloride-sensitive transepithelial Na transport and that their Na/K-pump activity is very low.

Amiloride↗