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PubMed1987

Trace elements during the development of hypertension in the spontaneously hypertensive rat.

Total plasma concentrations of bromine, copper, rubidium, selenium and zinc were measured in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) of 5-20 weeks of age, using an X-ray fluorescence spectrometry technique. Although plasma levels of bromine, rubidium, selenium and zinc varied at different ages when comparing SHR and WKY, their general evolution was similar. Copper levels increased more in SHR than in WKY. These perturbations in trace element levels could perhaps participate in the establishment of hypertension in SHR, but could also be due to genetic differences between the strains, unrelated to the development of hypertension.

Animals↗
PubMed1987

Erythrocyte cation fluxes during the menstrual cycle in normal female subjects.

1. Studies of erythrocyte cation transport mechanisms in vitro were performed on eight normotensive, premenopausal female subjects at the mid-points of the follicular and luteal phases of their menstrual cycles. Concurrent plasma concentrations of 17 beta-oestradiol, progesterone, aldosterone and renin activity were measured. 2. Ouabain-resistant, frusemide-resistant rubidium influx (an index of passive potassium diffusion) was significantly lower in the luteal than the follicular phase. 3. In further studies in four of the eight subjects, the mean rate constant of the rubidium influx measurement was also lower in the luteal than in the follicular phase. 4. There were no changes in Na+-K+ co-transport, sodium pump activity or intracellular cation concentrations throughout the cycle. 5. There was a tenfold fall in the mean plasma 17 beta-oestradiol/progesterone ratio, as well as increases in plasma aldosterone concentration and renin activity between the mid-follicular and mid-luteal phases. 6. We conclude that changes in plasma oestrogen/progesterone ratio during the menstrual cycle may be associated with alterations in passive potassium diffusion.

Adult↗
PubMed1997

A mechanism for regulatory volume decrease in cultured lens epithelial cells.

PURPOSE: To identify mechanisms contributing to regulatory volume decrease in lens epithelial cells. METHODS: Cells of the lens epithelial cell line alpha TN4 were cultured in four-well culture dishes in Dulbecco's Modified Eagle Medium containing 10% fetal bovine serum. After confluence cell water space was determined by measuring the equilibrium distribution of 3-O-methylglucose. Potassium influx and efflux in isotonic and hypotonic solutions were measured using 86rubidium (86Rb) as tracer. Total cell potassium and sodium content were determined with atomic absorption spectroscopy. Protein content per well was assayed with a modified Lowry assay and flux data and ion concentrations were normalized per mg of protein. RESULTS: Lens epithelial cells responded to hypotonic solutions with rapid swelling followed by regulatory volume decrease (RVD). During swelling and subsequent volume decrease the unidirectional Rb efflux was increased proportionaly to the osmotic challenge. Rubidium efflux was highly sensitive to changes in extracellular osmolarity and responded with a measurable activation to changes of 12.5 mOsm. No changes in 86Rb influx were observed with small changes (< 20%) in osmolarity and only relatively small changes occurred with larger changes in osmolarity. The resulting net loss of 86Rb and potassium (K+) was demonstrated by measuring the change of intracellular [K+] in hypotonic solutions using atomic absorption spectroscopy. The K(+)-channel blockers quinine-HCl and BaCl2 and the Cl(-)-channel blockers diphenyl-2-carboxylate (DPC) and 5-nitro-2-(3-phenyl propylamino) benzoic acid (NPPB) did not significantly affect the 86Rb efflux induced by hypotonic solutions. However, [(dihydroindenyl)oxy]alkanoic acid (DIOA), reported to be a specific inhibitor of the K-Cl cotransporter, inhibited the activation of 86Rb efflux. 86Rb efflux could be activated in isosmotic solutions by the addition of 1 mM N-ethylmaleimide (NEM). This activation of Rb efflux could be prevented by the addition of 1 mM dithiothreitol and could be 90% blocked by DIOA. The activation of rubidium efflux by NEM led to a significant decrease of the intracellular water content. The volume regulatory changes in NEM and in hypotonic solutions could be inhibited in DIOA. CONCLUSIONS: The observations are consistent with the presence in lens epithelial cells of a K-Cl cotransporter serving as a mechanism for regulatory volume decrease.

3-O-Methylglucose↗
PubMed2005

Combination of glycemic and oxidative stress in lens: implications in augmentation of cataract formation in diabetes.

It is well known that the incidence of cataract is higher in diabetics as compared to non-diabetics. Its rate of maturation is also faster in the diabetics. The precise mechanism of this acceleration is not clearly understood. It is hypothesized that this could be a result of the combination of the metabolic and oxidative stress induced by glycemia itself with the age-associated increase in ambient generation of oxyradical species. In the current studies, we have investigated this possibility using the galactose cataract model. Galactosemia was induced by feeding rats a 50% galactose diet. The increased susceptibility of the glycemic lenses to physiological damage by reactive oxygen species (ROS) was studied by incubating them in Tyrode in the absence and presence of menadione. The resulting physiological damage to the lens was assessed initially in terms of its ability to maintain Na+-K+ ATPase dependent active transport of potassium ions, as represented by the uptake of rubidium ions. Subsequently, the level of ATP, indexing the general metabolic status, and the level of glutathione (GSH), indexing the status of antioxidant reserve, were also determined. The uptake of rubidium in the normal lenses incubated in the presence of the quinone was depressed to more than 50% of the controls run in the basal medium. A similar depression existed in the galactosemic lenses in comparison to the normal lenses. However, in the presence of menadione, the inhibition of the uptake was accentuated further in the case of galactosemic lenses, the uptake here being only 20% of the normal controls. Similarly, the galactosemic lenses were also more susceptible to menadione dependent decrease in ATP and GSH.

Adenosine Triphosphate↗
PubMed1985

Intestinal circulation during inhalation anesthesia.

This study was designed to evaluate the influence of inhalational agents on the intestinal circulation in an isolated loop preparation. Sixty dogs were studied, using three intestinal segments from each dog. Selected intestinal segments were pumped with aortic blood at a constant pressure of 100 mmHg. A mixture of 86Rb and 9-microns spheres labeled with 141Ce was injected into the arterial cannula supplying the intestinal loop, while mesenteric venous blood was collected for activity counting. A very strong and significant correlation was found between rubidium clearance and microsphere entrapment (r = 0.97, P less than 0.0001), suggesting that the shunting of 9-microns spheres through the intestines reflects the arteriovenous shunting of blood. Nitrous oxide anesthesia was accompanied by a higher vascular resistance (VR), lower flow (F), rubidium clearance (Cl-Rb), and microspheres entrapment (Cl-Sph) than pentobarbital anesthesia, indicating that the vascular bed in the intestinal segment was constricted and flow (total and nutritive) decreased. Halothane, enflurane, and isoflurane anesthesia were accompanied by a much lower arteriovenous oxygen content difference (AVDO2) and oxygen uptake than pentobarbital or nitrous oxide. Compared with pentobarbital, enflurane anesthesia was not accompanied by marked differences in VR, F, Cl-Rb, and Cl-Sph; halothane at 2 MAC decreased VR and increased F and Cl-Rb while isoflurane increased VR and decreased F. alpha-Adrenoceptor blockade with phentolamine (1 mg . kg-1) abolished isoflurane-induced vasoconstriction, suggesting that the increase in VR was mediated via circulating catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMedDate not supplied

Considerations of 201T1 as a myocardial radionuclide imaging agent in man.

Recent reports have suggested the use of intravenous 201T1 (thallium-201) for myocardial imaging with the gamma scintillation camera. In order to better appreciate the possible utility of this agent in humans we examined its distribution and kinetics in 13 patients and in six mongrel dogs, three with experimental coronary artery occlusion. In addition, 201T1 was compared to 86Rb (rubidium-86) in 84 rats. In the rat heart, the concentration of 201T1 was 30% higher than that of 86Rb ten minutes after injection. Moreover, myocardium-to-blood ratios for 201T1 averaged 51:1, but only 32:1 for 86Rb ten minutes after administration. In the dog heart, the distribution of 201T1 paralleled that of radioiodinated (131I) albumin particles injected into the left atrium and, thus, appears to be related to regional blood flow. Its concentration in ischemic regions decreased to 32.3% of the normally perfused myocardium. In the patients with a recent or old myocardial infarction, areas of decreased 201T1 uptake were easily identified and corresponded in location to that by ECG. Repeat scans 24 hours after the initial injection showed a significant retention of 201T1 by the myocardium. 201T1 blood levels in humans 15 minutes after injection were low (averaging 1.06% +/- 0.41% SD of the total dose per liter) and these levels decreased with a biological half-life of 3.1 +/- 0.7 days. Twenty-four hour urinary excretion rates ranged from 0.6 to 6.5% of the total dose and appeared related to urinary flow and the concentation of 201T1 in blood. Because of the higher target to background ratios, 201T1 compares favorably with radioactive rubidium. 201T1 in diagnostic doses remained without detectable adverse effects and appears promising as an agent for visualizing abnormal regional myocardial perfusion in patients with coronary artery disease.

Adult↗
PubMed2002

Renal Na-K-Cl cotransporter NKCC2 in Dahl salt-sensitive rats.

BACKGROUND: Dahl salt-sensitive (DS) rats are characterized by enhanced NaCl reabsorption in the loop of Henle, but the responsible ion transport protein is unknown. OBJECTIVE: To investigate renal Na-K-Cl cotransporter NKCC2 function and expression in DS rats under a low-salt diet. METHODS: NKCC2 functioning was assessed in vitro by measuring bumetanide-sensitive rubidium uptake and cytosolic chloride concentration in isolated medullary thick ascending limb (mTAL) tubules, and in vivo by measuring the salidiuretic action of orally given bumetanide. NKCC2 expression was assessed by Western blot analysis of outer medullary proteins using T4 monoclonal antibody. RESULTS: mTAL tubules from DS rats exhibited significantly higher bumetanide-sensitive rubidium uptake (85.1 +/- 4.8 versus 66.2 +/- 4.4 nmol/min per mg protein in DS and DR, (Dahl salt-resistant) rats, respectively; P = 0.011) and significantly higher cytosolic chloride (32.8 +/- 1.7 versus 25.0 +/- 1.5 mmol/l in DS and DR rats, respectively). Moreover, DS rats showed a significantly higher (P < 0.001) natriuretic response to bumetanide (1.13 +/- 0.05 versus 0.64 +/- 0.09 mmole/3 h in DS and DR rats, respectively). Finally, Western blot analysis revealed less NKCC2 expression in DS rats. CONCLUSIONS: We conclude that DS rats have increased renal NKCC2 activity, thus explaining, at least in part, their genetic renal inability to excrete sodium. Moreover, DS rats have a decreased renal NKCC2 expression, which can be a compensatory phenomenon against NKCC2 hyperactivity.

Animals↗
PubMed2005

Structure of gramicidin D-RbCl complex at atomic resolution from low-temperature synchrotron data: interactions of double-stranded gramicidin channel contents and cations with channel wall.

Gramicidin D (gD) is a naturally occurring ionophoric antibiotic that forms membrane channels specific for monovalent cations. The crystal structure of the RbCl complex of gD has been determined at 1.14 A resolution from low-temperature (100 K) synchrotron-radiation data with a final R of 16%. The structure was refined with anisotropic temperature factors for all non-H atoms and with partial occupancies for many of them. The asymmetric unit in the crystal contains four crystallographically independent molecules that form two right-handed antiparallel double-stranded dimers. There are seven distinct rubidium-binding sites in each dimeric channel. The occupancy factors of Rb cations are between 0.11 and 0.35 and the total ion contents of the two crystallographically independent channels are 1.59 and 1.22 ions, respectively. Although each channel is 'chemically symmetrical', the side-chain conformations, the distributions of rubidium cations and their binding sites in the two independent channels are not. Cations are 'coordinated' by delocalized pi-electrons of three to five carbonyl groups that together with peptide backbone chains form the gramicidin channel walls. The water:cation ratio in the channel interior is four or five:one, and five or six waters separate Rb cations during their passage through the channel.

Binding Sites↗
PubMed1982

Renal medullary blood flow studied with the 86-Rb extraction method. Methodological considerations.

The 86-Rb extraction method was applied for a study of regional renal blood flow. In the cortex, a sampling time of 30 s led to an underestimation by about 15% as compared with the microsphere method. This was due to incomplete cortical cellular extraction of rubidium with subsequent rapid wash-out the tracer. In the renal medulla, a sampling of 30-60 s gave valid data with almost complete extraction. A sampling time of only 10 s, i.e. a time similar to the intravascular transit time, gave rise to a 50% underestimation of the inner medullary blood flow. Errors due to transport of rubidium by the tubular fluid were investigated in detail. A theoretical analysis based on equilibrium data revealed a maximal error of about 5%. Studies with micropuncture of distal tubules and studies of the urinary transport showed no or negligible contamination from tubular urine. Under control antidiuretic conditions the blood flow in the cortex was 5.2 +/- 0.2 ml . min-1 . g-1 (mean +/- SE, n = 16), in the outer stripe of the outer zone 2.2 +/- 0.1, in the inner stripe 1.5 +/- 0.1 and in the inner zone 0.69 +/- 0.06.

Animals↗
PubMed1979

Cyclic GMP and the permeability of the disks of the frog photoreceptors.

1. The diffusion of sodium, potassium and rubidium (not chloride) ions across the disk membrane is increased by cyclic guanosine monophosphate (cyclic GMP). 2. The increase is greater for sodium than for rubidium in the 0.01-0.1 mM concentration range. 3. Cyclic adenosine monophosphate (cyclic AMP) is less efficient than cyclic GMP; GMP and guanosine triphosphate are without effect. 4. The effect is present with either 1.8 mM calcium ions or 4 mM-EGTA in the perfusion fluid. 5. The presence of the cyclic GMP phosphodiesterase on the disk membranes is not needed for this effect. 6. The effect is present in both unbleached and fully bleached membranes.

Animals↗
PubMed1993

A mechanism for ion selectivity in potassium channels: computational studies of cation-pi interactions.

A combination of computational methods has been used to evaluate the interaction between the pi face of a benzene molecule and the monovalent cations of lithium, sodium, potassium, and rubidium. In the gas phase, the ions are strongly bound, and the affinity for benzene follows the expected electrostatic trend (lithium, largest; rubidium, smallest). However, in an aqueous environment, a reordering occurs such that the potassium ion is preferred over all the other ions for 2:1 benzene:ion complexes. The selectivity sequence parallels that seen in voltage-gated potassium channels. Given that several conserved aromatic residues are present in the pore region of such channels, these results suggest that the cation-pi interaction may be responsible for the ion selectivity in potassium channels.

Amino Acid Sequence↗
PubMed1981

Familial abnormality of erythrocyte cation transport in essential hypertension.

Cation transport across the red-cell membrane was studied in subjects with essential hypertension and their relatives using rubidium-86 as an analogue of potassium. The activity of the ouabain-sensitive sodium-potassium pump was significantly greater in patients with untreated essential hypertension than in controls (p less than 0.001). No clear separation was seen between normotensive and hypertensive subjects. Activity of the sodium-potassium pump was also increased in a proportion of normotensive relatives of subjects with essential hypertension. Rubidium uptake was significantly lower in normotensive black subjects than in normotensive whites, the difference being in a ouabain-resistant pathway of cation transport. These results provide further evidence that a defect in membrane cation transport contributes to the pathogenesis of essential hypertension.

Adult↗
PubMed1991

In vivo and in vitro sodium pump activity in subjects with thyrotoxic periodic paralysis.

OBJECTIVE: To examine whether sodium pump activity plays a part in the pathogenesis of thyrotoxic periodic paralysis. DESIGN: Measurement of platelet sodium-potassium ATPase and in vivo sodium pump activities in healthy subjects and thyrotoxic subjects with and without paralysis. SETTING: University hospital in Hong Kong. SUBJECTS: 21 healthy subjects, 23 untreated thyrotoxic subjects, 13 untreated men with periodic paralysis, seven treated thyrotoxic subjects, and six treated men with periodic paralysis. MAIN OUTCOME MEASURES: Platelet Na+, K(+)-ATPase activity and plasma rubidium concentration after oral loading. RESULTS: Median (range) platelet Na+, K(+)-ATPase activity in thyrotoxic subjects was 253 (169-821) mumol inorganic phosphate/h/g protein--significantly higher than that in healthy subjects (134 (81-180) mumol/h/g protein; p less than 0.001). Na+, K(+)-ATPase activity in those with periodic paralysis was 374 (195-1196) mumol/h/g protein, again significantly higher than that in healthy subjects (p less than 0.001) and that in other thyrotoxic subjects (p less than 0.01) despite similar degrees of hyperthyroidism. Activities in treated thyrotoxic subjects with and without periodic paralysis were 148 (110-234) and 131 (86-173) mumol/h/g protein respectively. Mean (95% confidence interval) plasma rubidium concentration five hours after oral administration in thyrotoxic subjects (7.0 (6.6 to 7.5) mumol/l) was significantly lower than in healthy subjects (10.2 (9.5 to 10.9) mumol/l; p less than 0.001) and higher than in those with periodic paralysis (6.0 (5.7 to 6.3) mumol/l; p less than 0.01). CONCLUSIONS: Sodium pump activity in untreated subjects with periodic paralysis is higher than in other thyrotoxic subjects, and this may be responsible for the hypokalaemia.

Adult↗
PubMed1990

The interrelationship of cesium, intracellular sodium activity, and pacemaker potential in cardiac Purkinje fibers.

The actions of cesium (Cs) on intracellular sodium activity (aiNa), membrane potentials, and force were studied in sheep cardiac Purkinje and myocardial fibers superfused in vitro. In Purkinje fibers, Cs (2 mM) decreased diastolic depolarization, aiNa (-6.7%, p less than 0.005), and force (-28.0%, p less than 0.01). The effects of 4 and 8 mM Cs were more pronounced. In quiescent fibers, Cs (2-4 mM) also decreased aiNa (-17.3%, p less than 0.005) and induced an initial hyperpolarization (+5.6 +/- 1.3%, p less than 0.005) followed by a return toward control. Diastolic depolarization was almost abolished by driving the fibers at 180/min (diastole was very short) but still Cs decreased aiNa (-15.4%). Tetrodotoxin decreased aiNa (-16.2%, p less than 0.025) and reduced the Cs-induced fall in aiNa (-2.2%, p less than 0.05). In zero [K]o, Cs decreased aiNa and caused repolarization. In 0.1 mM strophanthidin, Cs did not decrease aiNa any longer and affected the membrane potential little. In quiescent myocardial fibers, Cs (4 mM) decreased aiNa (-12.6%, p less than 0.05) and transiently hyperpolarized (+2.1%). Rubidium (2 mM) decreased aiNa and resting potential in Purkinje fibers and in myocardial fibers and also decreased diastolic depolarization in Purkinje fibers. Thus, cesium and rubidium decrease aiNa and modify the membrane potential but not through a block of the inward pacemaker current If.

Animals↗
PubMed1985

Regulation of jejunal blood flow and oxygenation during glucose and oleic acid absorption.

To differentiate the mechanisms whereby actively absorbed glucose and passively absorbed oleic acid increase blood flow and oxygen uptake during their absorption, the effects of these two nutrients on jejunal blood flow, arteriovenous oxygen difference [(a-v)O2], O2 uptake, absorption, rubidium extraction, and capillary permeability-surface area product (PS) were compared in anesthetized dogs. Oleic acid (37 mM) produced significantly greater hyperemia (+28.2%) than glucose (270 mM) did (+12.5%). As estimated by (a-v)O2, tissue oxygen extraction was decreased by oleic acid (-12%) but increased by glucose (+6.5%); the increases in O2 uptake by these two nutrients did not differ significantly. Glucose absorption was accompanied by an increase in rubidium extraction and capillary PS (+11.3%), whereas oleic acid absorption was not. Unlike glucose, intra-arterial infusion of oleic acid decreased vascular resistance and increased blood flow equally to the mucosa and muscularis layers. A significant relation existed between oleic acid absorption and blood flow but not between glucose absorption and blood flow. The enhancement of glucose-induced hyperemia by bile was not related to glucose absorption. Unmasking of oleic acid-induced hyperemia by bile is unrelated to oleic acid absorption but is related to solubility of oleic acid in aqueous solution. The above findings suggest that glucose absorption affects both resistance and exchange vessels, whereas oleic acid absorption affects primarily resistance vessels.

Animals↗
PubMed1977

Effect of potassium on utilization of (1-14C)palmitic acid in renal cortex of the rat.

The renal cortex has an unusually high rate of palmitic acid utilization. The uptake, oxidation, and distribution of this fatty acid in the cortex, unlike other tissues, responds to variations in medium and tissue potassium content. This potassium dependency is mimicked and amplified by rubidium. These observations indicate that in the renal cortex, both potassium and rubidium promote the accumulation, oxidation, and esterification of palmitic acid.

Animals↗
PubMed1975

Thallium-201 for myocardial imaging. Relation of thallium-201 to regional myocardial perfusion.

Following intravenous administration, the myocardial concentration of tracer thallium-201, potassium-43, and rubidium-81 were determined in mice; thallium was present in the greatest concentration in the myocardium (2.08% compared 1.25% for potassium and 1.15% for rubidium at 10 minutes). The regional myocardial distribution of thallium-201 was determined in dogs under conditions of normal flow, and total occlusion, and compared with potassium-43 (r=0.97). The regional distribution of thallium-201 was compared to microspheres under conditions of partial occlusion and reactive hyperemia (r=0.97). Thallium-201 was evaluated in a series of phantom scans, which demonstrated that the low energy X-ray of thallium was suitable for imaging. These results suggest that thallium-201 can be used for the evaluation of the distribution of regional myocardial perfusion.

Animals↗
PubMed2001

Rapid modulation of Na+/K+-ATPase activity in osmoregulatory tissues of a salmonid fish.

The effects of cyclic AMP on Na+/K+-ATPase activity were studied in the gill and kidney of the euryhaline brown trout Salmo trutta using two different experimental approaches. In the first series of experiments, in situ Na+/K+-ATPase activity was analyzed by measuring the ouabain-sensitive uptake of non-radioactive rubidium (Rb+) into gill cells and blocks of gill and kidney tissue. Rubidium uptake was linear for at least 30 min and was significantly inhibited by 1 mmol x l(-1) ouabain. Several agents presumed to increase the intracellular cyclic AMP concentration inhibited ouabain-sensitive Rb+ uptake in both gill (0.5 and 2 mmol x l(-1) dibutyryl-cyclic AMP, 1 mmol x l(-1) theophylline, 10 micromol x l(-1) forskolin and 10 micromol x l(-1 )isoproterenol) and kidney (10 micromol x l(-1) forskolin) tissue from freshwater-acclimated fish. In a separate series of experiments, ATP hydrolase activity was assayed in a permeabilised gill membrane preparation after incubation of tissue blocks with 10 micromol x l(-1 )forskolin. Forskolin elevated gill cyclic AMP levels 40-fold, inhibited maximal enzymatic Na+/K+-ATPase activity (Vmax) in gill tissue from both freshwater- and seawater-acclimated fish and reduced the apparent K+ affinity in the gills of seawater-acclimated fish, demonstrating that the effects are mediated through modifications of the enzyme itself. The protein phosphatase inhibitors okadaic acid and cyclosporin A did not affect forskolin-induced inhibition of Na+/K+-ATPase activity, indicating that forskolin-mediated modulation was stable for the duration of assay. We suggest that cyclic-AMP-mediated phosphorylation through protein kinases may underlie the rapid modulation of Na+/K+-ATPase activity in the osmoregulatory tissues of euryhaline teleosts.

Animals↗