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[Studies on changes in trace elements of the brain related to aging].

This study was performed to determine whether trace elements in the brain are linked to its aging, using the senescence-accelerated mouse prone10 (SAMP10) established as a murine model of aging with brain atrophy and defect in learning and memory. First, concentrations of trace elements (zinc, copper, manganese, molybdenum, and rubidium) were determined by ICP-MS in 8 regions of the brain in male SAMP10 and in SAMR1 (control) which undergo ordinary aging, at 3, 6, 9 and 12 months of age. Second, the release of glutamic acid and other amino acids related to neurotransmission was determined by microdialysis and HPLC-ECD in the hippocampus of SAM aged 5 and 12 months. Decreases in zinc, manganese and rubidium concentrations and an increase in the copper concentration with aging were observed in the brains of control mice. These results were similar to previous reports of the brain in human and rat, and indicated that these trace elements may be closely related to the aging process in the brain. SAMP10 had low levels of zinc and manganese in most brain regions in old age, and a high level of molybdenum in the brain with increasing age as compared to the control. A low level of copper was observed in the cerebral cortex of the brain in SAMP10 from young age. The release of glutamic acid and glycine from the hippocampus of SAMP10 significantly increased as compared to that of control mice at the age of 12 months. These results showed that abnormal metabolisms of the trace elements and neurotransmitter are in the brain of SAMP10, and indicated that these changes may cause the senescence acceleration of SAMP10.

Aging↗

Evidence of a phase transition of RbHCO3 from high-resolution solid-state 13C and 87Rb NMR by comparison with KHCO3.

A variable-temperature high-resolution 13C and 87Rb solid-state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low-temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non-ferroic, non-ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double-well potential in the low-temperature phase, and the double-well potential becomes symmetric in the high-temperature phase. By comparison with recent solid-state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc approximately 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar.

Algorithms↗

Rb+ occlusion in renal (Na+ + K+)-ATPase characterized with a simple manual assay.

This paper describes properties of a simple manual assay for Rb+ occlusion on renal (Na+ + K+)-ATPase. Rb+ occlusion is measured by applying the enzyme plus Rb+ (86Rb) mixture to a Dowex-50 cation exchange column at 0 degree C, and eluting the enzyme with occluded Rb+ using an ice-cold sucrose solution. The enzyme-Rb+ complex is quite stable at 0 degree C. This method is useful for measuring Rb+ occlusion under equilibrium binding conditions and slow rates of dissociation of the enzyme-Rb+ complex. The stoichiometry of Rb+ occluded per phosphorylation site is 2. Rb+ saturation curves are strictly hyperbolic, suggesting that the two Rb+ sites have very different affinities, one in the micromolar range and one in the tens of millimolar range. ATP shifts the Rb+ saturation curves to the right (control K0.5 100-200 microM; plus ATP, K0.5 0.8-1.4 mM, in a 100 mM Tris-HCl medium, pH 7.0) and reduces the maximal level occluded (control approx. 4 nmol/mg; plus ATP approx. 3 nmol/mg protein). Thus, as expected, ATP shifts the E(1)2Rb+-E2(2Rb+)occ equilibrium towards E1. Sodium ions at concentrations of up to 30 mM compete with the rubidium ions, KNa = 1.86 mM in the Tris-HCl medium. Na+ at higher concentrations (30-100 mM) has an added non-competitive antagonistic effect. At room temperature, Rb+ dissociates slowly from the enzyme, kobs = 0.08 s-1, in the presence of either Rb+ (20 mM) or Na, (100 mM). As expected, dissociation is greatly accelerated by ATP, the rate being to fast to be measured by this technique. (Na+ + K+)-ATPase proteolyzed selectively by chymotrypsin in a Na+ medium, occludes Rb+. For control and proteolyzed (Na+ + K+)-ATPase the Rb+ saturation curves are similar and the rates of dissociation of the enzyme-Rb+ complex are identical. The chymotryptic split appears to disrupt antagonistic interactions between cation and ATP binding domains, while the E1-E2 conformational transition of the unphosphorylated protein probably remains.

Adenosine Triphosphate↗

Effect of Rb+ on cromakalim-induced relaxation and ion fluxes in guinea pig trachea.

The effects of cromakalim, verapamil and salbutamol have been examined in guinea pig trachealis smooth muscle in both Krebs physiological salt solution and Krebs solution where K+ has been replaced by Rb+. Cromakalim-induced relaxation in the presence of Rb+ was reduced in extent and became transient, whilst the relaxation response to verapamil was enhanced and that to salbutamol unaffected. The transient relaxation occurring in Rb+ was blocked by quinidine and glibenclamide. The presence of extracellular Rb+ also prevented cromakalim-stimulated efflux of both 86Rb+ and 42/43K+. There was, however, no effect on cromakalim-stimulated 86Rb+ uptake. It is proposed that cromakalim is opening two populations of potassium channel in guinea pig tracheal smooth muscle, one of which is susceptible to blockade by Rb+ and one of which is not. The latter channel appears to play the dominant role in cromakalim-stimulated uptake, and is responsible for the transient relaxation response in the presence of rubidium, whilst the former is responsible for the maintained relaxation.

Albuterol↗

Cognitive impairment in spontaneously hypertensive rats: role of central nicotinic receptors. Part II.

The adult spontaneously hypertensive rat (SHR) has been shown to exhibit a decrease in the expression and nicotine-stimulated function of brain nicotinic acetylcholine receptors, factors that could play a role in the impaired ability of this strain in the performance of learning and memory-related tasks. The purpose of this study was to determine whether either or both the impaired task performance and the loss of nicotinic receptors is directly related to the presence of the hypertensive state. To address this issue, two experimental approaches were taken. In the first series, 4-week-old pre-hypertensive SHR were tested in two phases of a water maze (spatial memory) task, and their performance was compared with that of two age-matched normotensive strains, Wistar Kyoto (WKY) and Wistar rats. During phase 1, SHR and WKY rats were not different in their ability to learn the task. In contrast, during phase 2 (subsequent series of trials after a 4 day inter-phase period), where rats were required to find a new platform location, SHR exhibited significantly impaired performance compared to both WKY and Wistar normotensive controls. In a single trial passive avoidance paradigm, SHR again displayed significantly reduced avoidance behavior as compared with both WKY and Wistar rats. In consecutive coronal sections the density of [3H]cytisine binding sites was decreased in pre-hypertensive SHR by up to 18% in about 40% of the brain regions examined, with the deficits particularly apparent in frontal cortex (layers 4-6), posterior subiculum, several thalamic regions, and the interpeduncular nucleus. In the second series, age-matched SHR and WKY were treated with the antihypertensive agent hydralazine administered in the drinking water beginning at 4 weeks of age. Hydralazine prevented the development of hypertension in adult SHR, but did not forestall the reduced expression of brain nicotinic receptors, nor the impairment in learning- and memory-related tasks normally observed in untreated adults with established hypertension. Moreover, the magnitude of nicotine-stimulated rubidium efflux from cortical and striatal synaptosomes in vitro was significantly reduced in samples derived from hydralazine-treated SHR as compared with those from hydralazine-treated, or untreated WKY. These results support the contention that the hypertensive state does not directly contribute to the reduced expression of nicotinic receptors in SHR. Therefore, the SHR may provide an important genetic model for the study of the role of central nicotinic receptors in cognitive and learning abnormalities.

Aging↗

Alteration of alpha 1 Na+,K(+)-ATPase 86Rb+ influx by a single amino acid substitution.

The sodium- and potassium-dependent adenosine triphosphatase (Na+,K(+)-ATPase) maintains the transmembrane Na+ gradient to which is coupled all active cellular transport systems. The R and S alleles of the gene encoding the Na+,K(+)-ATPase alpha 1 subunit isoform were identified in Dahl salt-resistant (DR) and Dahl salt-sensitive (DS) rats, respectively. Characterization of the S allele-specific Na+,K(+)-ATPase alpha 1 complementary DNA identified a leucine substitution of glutamine at position 276. This mutation alters the hydropathy profile of a region in proximity to T3(Na), the trypsin-sensitive site that is only detected in the presence of Na+. This mutation causes a decrease in the rubidium-86 influx of S allele-specific sodium pumps, thus marking a domain in the Na+,K(+)-ATPase alpha subunit important for K+ transport, and supporting the hypothesis of a putative role of these pumps in hypertension.

Amino Acid Sequence↗

Measurements of mitochondrial K+ fluxes in whole rat hearts using 87Rb-NMR.

The rubidium efflux from hypothermic rat hearts perfused by the Langendorff method at 20 degreesC was studied. At this temperature 87Rb-NMR efflux experiments showed the existence of two 87Rb pools: cytoplasmic and mitochondrial. Rat heart mitochondria showed a very slow exchange of mitochondrial Rb+ for cytoplasmic K+. After washout of cytosolic Rb+, mitochondria kept a stable Rb+ level for >30 min. Rb+ efflux from mitochondria was stimulated with 0.1 mM 2, 4-dinitrophenol (DNP), by sarcolemmal permeabilization and concomitant cellular energy depletion by saponin (0.01 mg/ml for 4 min) in the presence of a perfusate mimicking intracellular conditions, or by ATP-sensitive K (KATP) channel openers. DNP, a mitochondrial uncoupler, caused the onset of mitochondrial Rb+ exchange; however, the washout was not complete (80 vs. 56% in control). Energy deprivation by saponin, which permeabilizes the sarcolemma, resulted in a rapid and complete Rb+ efflux. The mitochondrial Rb+ efflux rate constant (k) decreased in the presence of glibenclamide, a KATP channel inhibitor (5 microM; k = 0.204 +/- 0.065 min-1; n = 8), or in the presence of ATP plus phosphocreatine (1.0 and 5.0 mM, respectively; k = 0.134 +/- 0.021 min-1; n = 4) in the saponin experiments (saponin only; k = 0.321 +/- 0.079 min-1; n = 3), indicating the inhibition of mitochondrial KATP channels. Thus hypothermia in combination with 87Rb-NMR allowed the probing of the mitochondrial K+ pool in whole hearts without mitochondrial isolation.

2,4-Dinitrophenol↗

Dextran's effects on stressed lenses: water, electrolyte, and radioisotope studies.

To evaluate the beneficial effects of dextran 40 as an additive to infusion solutions, we studied an experimental model of lens stress with use of buffered, low calcium (Ca++)-containing solutions. Incubation in low Ca++ solutions (pCa = 10.7) for ten hours (stress period) resulted in lens swelling and electrolyte imbalances that were irreversible even with reincubation in physiologic, normal Ca++-containing media (pCa = 2.7) (recovery period). The addition of 6% or more of dextran to the media inhibited lens water gain during the stress period. It also rendered the resultant electrolyte imbalances reversible during the recovery period, thus exerting a protective effect. Radioisotope-tracer studies showed that dextran improved the ability of the lens to accumulate rubidium chloride Rb 86 and reduced its efflux during both the stress and recovery periods. Although dextran did not markedly decrease sodium chloride Na 22 uptake by lenses under stress, it did allow the lens to remove the 22Na during the recovery period.

Animals↗

Positron emission tomographic measurement of blood-to-brain and blood-to-tumor transport of 82Rb: the effect of dexamethasone and whole-brain radiation therapy.

Unidirectional blood-to-brain and blood-to-tumor transport rate constants for rubidium 82 were determined using dynamic positron emission tomography in patients with primary or metastatic brain tumors. Regional influx rate constants (K1) and plasma water volume (Vp) were estimated from the time course of blood and brain radioactivity following a bolus injection of tracer. Eight patients were studied before and 24 to 72 hours after treatment using pharmacological doses of dexamethasone, and 6 additional patients with metastatic brain tumors were studied before and within 60 to 90 minutes after 200- to 600-rad whole-brain radiation therapy. Steroid treatment was associated with a 9 to 48% decrease in tumor K1 and a 21% mean decrease in tumor Vp. No consistent changes in K1 or Vp were observed in control brain regions. Tumor K1 and Vp did not increase in patients undergoing whole-brain radiation therapy, all of whom were taking dexamethasone at the time of study. These data suggest that corticosteroids decrease the permeability of tumor capillaries to small hydrophilic molecules (including those of some chemotherapeutic agents) and that steroid pretreatment prevents acute, and potentially dangerous, increases in tumor capillary permeability following cranial irradiation.

Adult↗

Reduced cerebral glucose metabolism and increased brain capillary permeability following high-dose methotrexate chemotherapy: a positron emission tomographic study.

Regional glucose metabolic rate constants and blood-to-brain transport of rubidium were estimated using positron emission tomography in an adolescent patient with a brain tumor, before and after chemotherapy with intravenous high-dose methotrexate. Widespread depression of cerebral glucose metabolism was apparent 24 hours after drug administration, which may reflect reduced glucose phosphorylation, and the influx rate constant for 82Rb was increased, indicating a drug-induced alteration in blood-brain barrier function. Associated changes in neuropsychological performance, electroencephalogram, and plasma amino acid concentration were identified in the absence of evidence of systemic methotrexate toxicity, suggesting primary methotrexate neurotoxicity.

Acute Disease↗

Identification of ischemic and hibernating myocardium: feasibility of post-exercise F-18 deoxyglucose positron emission tomography.

The identification of ischemic and hibernating myocardium facilitates the selection of patients most likely to benefit from revascularization. This study examined the feasibility of metabolic imaging, using post-exercise F-18 deoxyglucose positron emission tomography (FDG-PET) for the diagnosis of both ischemia and hibernation in 27 patients with known coronary anatomy. Normal post-exercise FDG uptake was defined in each patient by reference to normal resting perfusion and normal coronary supply. Abnormal elevation of FDG (ischemia or hibernation) was compared in 13 myocardial segments in each patient, with the results of dipyridamole stress perfusion imaging performed by rubidium-82 positron emission tomography (Rb-PET). Myocardial ischemia was diagnosed by either FDG-PET or Rb-PET in 34 segments subtended by significant local coronary stenoses. Increased FDG uptake was present in 32/34 (94%) and a reversible perfusion defect was identified by Rb-PET in 22/34 (65%, p less than .01). In 3 patients, ischemia was identified by metabolic imaging alone. In 16 patients with previous myocardial infarction, perfusion defects were present at rest in 89 regions, 30 of which (34%) demonstrated increased FDG uptake, consistent with the presence of hibernation. Increased post-exercise FDG uptake appears to be a sensitive indicator of ischemia and myocardial hibernation. This test may be useful in selecting post-infarction patients for revascularization.

Coronary Disease↗

Structural phase transitions in heavy alkali metals under pressure.

We performed a theoretical study of the crystal structures of cesium and rubidium under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs III and Rb III phases. The calculated transition pressures agree extremely well with the measured data. Thus, it is now certain that the famous isostructural phase transition in cesium is actually a new crystallographic phase transition. A d-orbital occupation number of about 0.52 is crucial for the occurrence of these complex structures.

Cesium↗

Effects of ouabain and ortho vanadate on transport-related properties of the LLC-PK1 renal epithelial cell line.

Uptake of alpha-methyl-D-glucoside (AMG) by LLC-PK1 cells is inhibited by the uncoupler p-trifluoro-methoxyphenyl-hydrazone (FCCP) and by the absence of extracellular Na+, indicating that the transport system is energy- and Na+-dependent. We have previously demonstrated that transport of AMG by LLC-PK1 cells proceeds against a concentration gradient and is phlorizin-sensitive (Mullin et al., '80). Uptake of AMG was also inhibited by ouabain (OUA) but not by ortho-vanadate (VAN). Rubidium uptake also was affected by OUA but not by VAN. VAN, however, caused collapse of the three-dimensional domes of confluent LLC-PK1 monolayers much more rapidly and thoroughly than OUA. Since domes are presumably dependent upon the Na+ pump, yet VAN is not acting on transport-related functions of the OUA-sensitive (Na+ + K+)-ATPase, we hypothesize a direct effect of VAN on the water permeability of these cells. We also suggest that OUA does not act on these cells until domes collapse in normal course, and access of the OUA to the extracellular surface of antiluminal membranes is then achieved.

Animals↗

Stretch-induced growth of skeletal myotubes correlates with activation of the sodium pump.

Skeletal myotubes responded to passive stretch by increased amino acid uptake (as measured with [3H]alpha-aminoisobutyric acid), increased incorporation of amino acids into total cellular protein and myosin heavy chains, and increased accumulation of total cellular protein and myosin heavy chains. These alterations were preceded by an increase in the uptake of ouabain-sensitive rubidium-86 (86Rb+), a potassium tracer used to measure membrane sodium pump activity (Na+K+ATPase). This stretch-induced stimulation of 86Rb+ uptake resulted from a 60-70% increase in the Vmax of the Na pump with little change in the Km. [3H] ouabain binding studies showed no stretch-induced change in the number of membrane Na pumps, indicating that stretch activates the Na pumps that are already present on the cell surface. Since the stretch-induced increases in amino acid transport and amino acid incorporation into proteins were inhibited by ouabain, Na pump activation may be involved in stretch-induced cell growth of skeletal muscle cells by hypertrophy.

Aminoisobutyric Acids↗

Enzymatic modification of the surface carbohydrates of Friend erythroleukemic cells.

Surface carbohydrates of Friend erythroleukemic-cells were modified by treatment with the exoglycosidases, alpha-galactosidase, beta-galactosidase, and neuraminidase without affecting cell growth and viability either in the presence of absence of 1.8% DMSO as inducer. When cells were incubated with a combination of alpha-galactosidase and neuraminidase and then induced, they showed an increased rate of differentiation as measured by the formation of benzidine-positive cells. These enzymes used singly, or beta-galactosidase treatment alone, or in combination with neuraminidase, did not change the rate of differentiation. Cell-surface labeling and electrophoretic separation of the glycoconjugates revealed that two regions of approximate molecular weights of 195,000 and 185,000 were neuraminidase-sensitive and one other of molecular weight of about 75,000 was sensitive to alpha-galactosidase. Both untreated and the combined alpha-galactosidase, neuraminidase-modified cells exhibited the same rate of uptake of carbon-14 DMSO, ruling out the possibility that the observed increased rate of differentiation was due to faster penetration of DMSO into enzyme-treated cells. On the other hand, the decrease in the rate of uptake of rubidium-86, an analogue of K+, by treated-induced cells was significantly enhanced over that observed with untreated-induced cells, suggesting that alpha-galactosidase plus neuraminidase modification of the cell surface was affecting at least one of the early events occurring in the Friend erythroleukemic cell differentiation program.

Animals↗

Regulatory volume decrease in alveolar macrophages: cation loss is not correlated with changes in membrane recycling.

Alveolar macrophages regain their normal volume after swelling in hypo-osmotic solutions. This process, termed regulatory volume decrease (RVD), is initiated 3-5 minutes after exposure of cells to hypo-osmotic solutions, and by 30 min, near-normal volumes are attained. Volume decrease does not occur at 0 degrees C or in solutions in which Na+ has been replaced by K+, or Cl- by the impermeant anion gluconate. These results, as well as direct measurement of intracellular cations, indicate that decreases in cell volume result primarily from the loss of K+ and Cl- and are similar to RVD in lymphocytes. Kinetic analysis of cation loss, both by directly measuring changes in intracellular cation content and by assaying rubidium efflux, showed that cation loss occurred immediately upon media dilution. The rate of cation loss fit first-order kinetics and preceded both the initiation of volume decrease and the maximum increase in surface receptor number. These results suggest that the cation transporters responsible for RVD are located at the cell surface and that regulation of activity is not dependent on alterations in membrane movement.

Animals↗

K+ fluxes mediated by Na(+)-K(+)-Cl- cotransport and Na(+)-K(+)-ATPase pumps in renal tubule cell lines transformed by wild-type and temperature-sensitive strains of Simian virus 40.

The relative contributions of Na(+)-K(+)-ATPase pumps and Na(+)-K(+)-Cl- cotransport to total rubidium (Rb+) influx into primary cultures of renal tubule cells (PC.RC) and cells transformed either with the wild-type or a temperature-sensitive mutant of the simian virus 40 (SV40), were measured under various growth conditions. The Na(+)-K(+)-ATPase-mediated component represented 74% and 44-48% of total Rb+ influx into PC.RC and SV40-transformed cells, respectively. Proliferating transformed cells showed substantial ouabain-resistant bumetanide-sensitive (Or-Bs) Rb+ influx (41-45% of total) which indicated the presence of a Na(+)-K(+)-Cl- cotransport. The Or-Bs component of Rb+ influx was greatly reduced when temperature-sensitive transformed renal cells (RC.SVtsA58) grown in Petri dishes or on permeable filters were shifted from the permissive (33 degrees C) to the restrictive temperature (39.5 degrees C) to arrest cell growth. The ouabain-sensitive Rb+ influx mediated by the Na(+)-K(+)-ATPase, the total and amiloride-sensitive Na+ uptakes were not modified following inhibition of cell proliferation. A similar fall in the Or-Bs influx was obtained when renal tubule cells transformed by the wild-type SV40 (RC.SV) were incubated with the K+ channel blocker, tetraethylammonium (TEA) ion, which we had previously shown to arrest cell growth without affecting cell viability (Teulon et al.: J. Cell. Physiol., 151:113-125, 1992). Reinitiation of cell growth by removal of TEA or return to 33 degrees C of the temperature-sensitive cells restored the Or-Bs component of Rb influx. Taken together, these results indicate that the Na(+)-K(+)-Cl- cotransport activity is critically dependent on cell growth conditions.

Animals↗

The effects of drugs modulating K(+) transport on Rb(+) uptake and distribution in pig hearts following regional ischemia: (87)Rb MRI study.

The effects of drugs that can modulate passive permeability of K(+) into cardiomyocytes in normal and reperfusion-damaged cardiac muscle were assessed. Rubidium ion (Rb(+)) was used as a K(+) tracer and (87)Rb-MRI as a detection method. The left anterior descending artery (LAD) of isolated pig hearts perfused with Krebs-Henseleit buffer (KHB) was occluded for 2 h and subsequently reperfused for 2 h with KHB containing 4.7 mM RbCl instead of KCl. The buffer contained either a blocker of ATP-sensitive K(+) channels (K(ATP)), glibenclamide (Glib, 3 micro M), a K(ATP) opener, pinacidil (Pin, 10 micro M), a K(+)/Na(+)/2Cl(-) co-transporter inhibitor, bumetanide (Bum, 10 micro M) or no drug (control). Upon reperfusion three-dimensional (87)Rb MR images were acquired to obtain kinetics of Rb(+) uptake and its distribution. Areas at risk (AAR) and areas of necrosis were determined by Evans Blue and triphenyl tetrazolium chloride staining, respectively. Rb(+) uptake kinetics in the remote posterior (Pos) wall were similar in all groups. The kinetics remained monoexponential in the affected anterior (Ant) wall and the uptake rates were 32, 36, 37 and 21% of that in the Pos wall in the control, Glib, Pin and Bum groups, respectively. Infarct sizes determined histologically as a percentage of total ventricular (left + right) mass (14-22%) corresponded to sizes of areas with 20-40% of maximal Rb image intensity [I(Rb)(max), 15-22%], except for the Pin group (12.5 vs 21%). The sizes of areas with 20-50% of I(Rb)(max) (30-36%) closely correlated with those of AAR determined histologically (31-33%). Lactate dehydrogenase release did not differ in all groups. We conclude that: (1) reperfusion damage quickly inhibits Rb(+) uptake; (2) Rb(+) uptake in normal and reperfused tissue does not significantly depend on K(ATP) or the K(+)/Na(+)/2Cl(-) cotransporter; (3) areas with 20-40% of maximal image intensity correspond to infarct areas.

Animals↗