Coherent charge oscillations in a bilayer graphene double quantum dot

The coherent dynamics of a quantum mechanical two-level system passing through an anti-crossing of two energy levels can give rise to Landau-Zener-Stückelberg-Majorana (LZSM) interference. LZSM interference spectroscopy has proven to be a fruitful tool to investigate charge noise and charge decoherence in semiconductor quantum dots (QDs). Recently, bilayer graphene has developed as a promising platform to host highly tunable QDs potentially useful for hosting spin and valley qubits. So far, in this system no coherent oscillations have been observed and little is known about charge noise in this material. Here, we report coherent charge oscillations and [Formula: see text] charge decoherence times in a bilayer graphene double QD. The charge decoherence times are measured independently using LZSM interference and photon assisted tunneling. Both techniques yield [Formula: see text] average values in the range of 400-500 ps. The observation of charge coherence allows to study the origin and spectral distribution of charge noise in future experiments.

Particle-hole symmetry protects spin-valley blockade in graphene quantum dots

Particle-hole symmetry plays an important role in the characterization of topological phases in solid-state systems¹. It is found, for example, in free-fermion systems at half filling and it is closely related to the notion of antiparticles in relativistic field theories². In the low-energy limit, graphene is a prime example of a gapless particle-hole symmetric system described by an effective Dirac equation^3,4 in which topological phases can be understood by studying ways to open a gap by preserving (or breaking) symmetries^5,6. An important example is the intrinsic Kane-Mele spin-orbit gap of graphene, which leads to a lifting of the spin-valley degeneracy and renders graphene a topological insulator in a quantum spin Hall phase⁷ while preserving particle-hole symmetry. Here we show that bilayer graphene allows the realization of electron-hole double quantum dots that exhibit near-perfect particle-hole symmetry, in which transport occurs via the creation and annihilation of single electron-hole pairs with opposite quantum numbers. Moreover, we show that particle-hole symmetric spin and valley textures lead to a protected single-particle spin-valley blockade. The latter will allow robust spin-to-charge and valley-to-charge conversion, which are essential for the operation of spin and valley qubits.

Probing Two-Electron Multiplets in Bilayer Graphene Quantum Dots

We report on finite bias spectroscopy measurements of the two-electron spectrum in a gate defined bilayer graphene (BLG) quantum dot for varying magnetic fields. The spin and valley degree of freedom in BLG give rise to multiplets of six orbital symmetric and ten orbital antisymmetric states. We find that orbital symmetric states are lower in energy and separated by ≈ 0.4-0.8  meV from orbital antisymmetric states. The symmetric multiplet exhibits an additional energy splitting of its six states of ≈ 0.15-0.5  meV due to lattice scale interactions. The experimental observations are supported by theoretical calculations, which allow to determine that intervalley scattering and "current-current" interaction constants are of the same magnitude in BLG.

Spin-valley coupling in single-electron bilayer graphene quantum dots

Understanding how the electron spin is coupled to orbital degrees of freedom, such as a valley degree of freedom in solid-state systems, is central to applications in spin-based electronics and quantum computation. Recent developments in the preparation of electrostatically-confined quantum dots in gapped bilayer graphene (BLG) enable to study the low-energy single-electron spectra in BLG quantum dots, which is crucial for potential spin and spin-valley qubit operations. Here, we present the observation of the spin-valley coupling in bilayer graphene quantum dots in the single-electron regime. By making use of highly-tunable double quantum dot devices we achieve an energy resolution allowing us to resolve the lifting of the fourfold spin and valley degeneracy by a Kane-Mele type spin-orbit coupling of ≈ 60 μeV. Furthermore, we find an upper limit of a potentially disorder-induced mixing of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K$$\end{document}K and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K^{\prime}$$\end{document}K′ states below 20 μeV.

Understanding the interaction between spin and valley degrees of freedom in graphene-based quantum dots underpins their applications in electronics and quantum information. Here, the authors study the low-energy spectrum and resolve the spin-valley coupling in single-electron quantum dots in bilayer graphene.

Electron-Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots

Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron-hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g-factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B-fields. Our measurements agree well with tight-binding calculations for our device.

Einschränkung der myokardialen Perfusionsreserve bei Mikrovaskular-Angina (Syndrom X): Nachweis durch 99mTc-MIBI-SPECT

Ziel: An 22 Patienten mit typischer Angina pectoris und normalen Koronararterien (Mikrovaskular-Angina, Syndrom X) wurde geprüft, ob mit 99mTc-MIBI-SPECT eine Einschränkung der myokardialen Perfusionsreserve nachweisbar ist. Methode: Die Untersuchung mit 99rnTc-MIBI-SPECT erfolgte in Ruhe und unter Vasodilatation nach einer Infusion mit Dipyridamol im Vergleich zu einer normalen Datenbank. Eine normale myokardiale Perfusionsreserve wurde bei einer differenziellen 99mTc-MIBI-Aufnahme von > 20% angesehen. Ergebnisse: 2/22 (9%) der Patienten wiesen eine Perfusionsreserve <20% mit im Mittel 37% auf, 91 % der Patienten wiesen eine relativ oder absolut verminderte 99mTc-MIBI-Aufnahme unter Vasodilatation auf. Bei 9/22 (41 %) Patienten war die Perfusionsreserve relativ gemindert mit einer Zunahme der 99mTc-MIBI-Aktivität von 6%, bei 11/22 wurde eine Abnahme der 99mTc-MIBI-Aktivität um 13% unter Vasodilatation dokumentiert. Schlußfolgerung: Bei guter Bildqualität ist die 99mTc-MIBI-SPECT zur semiquantitativen Bestimmung der Perfusionsreserve bei Patienten mit Mikrovaskular-Angina geeignet.

The electronic transport of top subband and disordered sea in an InAs nanowire in the presence of a mobile gate

We performed measurements at helium temperatures of the electronic transport in an InAs quantum wire (R(wire) ∼ 30 kΩ) in the presence of a charged tip of an atomic force microscope serving as a mobile gate. The period and the amplitude of the observed quasi-periodic oscillations are investigated in detail as a function of electron concentration in the linear and non-linear regime. We demonstrate the influence of the tip-to-sample distance on the ability to locally affect the top subband electrons as well as the electrons in the disordered sea. Furthermore, we introduce a new method of detection of the subband occupation in an InAs wire, which allows us to evaluate the number of electrons in the conductive band of the wire.

Graphene-based charge sensors

We discuss graphene nanoribbon-based charge sensors and focus on their functionality in the presence of external magnetic fields and high frequency pulses applied to a nearby gate electrode. The charge detectors work well with in-plane magnetic fields of up to 7 T and pulse frequencies of up to 20 MHz. By analyzing the step height in the charge detector's current at individual charging events in a nearby quantum dot, we determine the ideal operation conditions with respect to the applied charge detector bias. Average charge sensitivities of 1.3 × 10(-3)e Hz(-1/2) can be achieved. Additionally, we investigate the back action of the charge detector current on the quantum transport through a nearby quantum dot. By varying the charge detector bias from 0 to 4.5 mV, we can increase the Coulomb peak currents measured at the quantum dot by a factor of around 400. Furthermore, we can completely lift the Coulomb blockade in the quantum dot.

Fabrication of coupled graphene-nanotube quantum devices

We report on the fabrication and characterization of all-carbon hybrid quantum devices based on graphene and single-walled carbon nanotubes. We discuss both carbon nanotube quantum dot devices with graphene charge detectors and nanotube quantum dots with graphene leads. The devices are fabricated by chemical vapor deposition growth of carbon nanotubes and subsequent structuring of mechanically exfoliated graphene. We study the detection of individual charging events in the carbon nanotube quantum dot by a nearby graphene nanoribbon and show that they lead to changes of up to 20% of the conductance maxima in the graphene nanoribbon, acting as a well performing charge detector. Moreover, we discuss an electrically coupled graphene-nanotube junction, which exhibits a tunneling barrier with tunneling rates in the low GHz regime. This allows us to observe Coulomb blockade on a carbon nanotube quantum dot with graphene source and drain leads.

Electronic excited states in bilayer graphene double quantum dots

We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features additional energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points over a large energy range. The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.

[Obstructive pulmonary diseases and pulmonary hypertension]

Pulmonary hypertension is a frequent complication of chronic obstructive pulmonary disease. Especially in patients with concurrent sleep apnoe syndrome (so called "overlap syndrome"), the risk for pulmonary hypertension is high. Pathophysiologically, both toxic effects (cigarette smoke) and alveolar hypoventilation can induce dysfunction of the pulmonary endothelium. Genetic factors and cytokines/growth factors released by inflammatory cells may induce remodeling of the pulmonary vessels. Pulmonary hypertension results, which is initially reversible, but gradually worsens over time. At present, therapeutic options include long term oxygen in addition to the treatment of the underlying disease. A subgroup of patients may profit of a specific therapy with sildenafil and other new substances. However, studies that define these subgroups need to be performed.

Specific immune recognition of pancreatic carcinoma by patient-derived CD4 and CD8 T cells and its improvement by interferon-gamma

Pancreatic carcinoma is a very aggressive disease and little is known about its immunobiology. We here describe the presence in pancreatic cancer patients of spontaneously induced functional CD4 and CD8 memory/effector T cells reactive to autologous tumor cells or to the pancreatic cancer associated antigen, MUC-1. Such specific cells were present in the bone marrow or peripheral blood of most of the 23 tested patients. Low dose stimulation of primary cultures of pancreatic cancer cells with 500 IU/ml IFN-gamma for 72 h enhanced HLA-I expression and induced the de novo expression of HLA-II molecules. This led to a much better immune recognition by autologous HLA-I restricted and purified CD8 T cells and allowed tumor cell recognition by HLA-II restricted purified CD4 T-helper cells. Thus, interferon-gamma appears to be a useful adjuvant cytokine to enhance the immunogenicity of a patients' tumor cells and their recognition by tumor reactive immune cells.

Effect of disinfectants on microbial ecology in model distribution systems

This research was conducted to assess the impact of various disinfectants on bacterial water quality within model distribution systems (i.e. annular reactors). After colonization with non-disinfected water, annular reactors were treated with relatively low doses of chlorine (0.4 mg/l), chlorine dioxide (0.15 mg/l), or chloramines (0.9 mg/l). Under the tested conditions, bacterial inactivation varied as a function of disinfectant type (ranking by efficiency per mg of oxidant: ClO2 > Cl2 > ClNH2) and sample type (bulk water vs. biofilm). Depending on the disinfectant, the log inactivation of suspended and attached bacteria were 0.7-1.2 and 0.5-1.0, respectively. The characterization of microbial communities in drinking water can be performed using biochemical and/or molecular methods. In this study, biochemical tests were used, showing that pseudomonad and pseudomonad-like bacteria, as in other studies, were the most predominant micro-organisms (e.g. Pseudomonas fluorescens, Brevundimonas vescularis). The ratio Gram-positive to Gram-negative organisms was 1 to 3. No drastic differences were observed between the non-treated and disinfected pipes. Based on the bacteriological data presented in these experiments, chlorine dioxide represents an alternative to chlorine for certain distribution systems.

Paramètres prédictifs de l'apparition des coliformes dans les réseaux de distribution d'eau d'alimentation

L'isolement sporadique de coliformes sur certains réseaux de distribution en période chaude et en absnce de tout épisode décelable de contamination (défaut de traitement, post-contamination) laisse supposer que la présence de ces germes dans l'eau pourrait être associée à la présence d'un biofilm important à la surface des canalisations.

Cette hypothèse a pu être vérifiée lors de cette étude, réalisée sur différents réseaux de la banlieue parisienne.

Ce travail a mis en évidence une relation entre la fréquence d'observation des coliformes sur les sites du réseau et le dépassement de seuils critiques pour quatre paramètres:

- le niveau de salissure bactériologique de l'eau évalué par le dénombrement de la flore bactérienne planctonique totale par microscopie en épifluorescence

- la température

- la consommation de matière organique biodégradable (CODB)

- la concentration en chlore libre résiduel.

Le degré d'exposition des sites d'un réseau de distribution a pu être estimé par comptabilisation des dépassements des seuils critiques pour ces quatre paramètres. Trois niveaux de risques croissants (sans risque, faiblement exposé et exposé) ont été établis correspondant à des fréquences de plus en plus importantes d'apparition des coliformes sur les sites du réseau de distribution.

Pour une semaine donnée, le calcul de la moyenne des dépassements simultanés des seuils critiques enregistrés sur l'ensemble des sites a permis de définir quatre niveaux de risques moyens d'apparition des coliformes sur l'ensemble des sites (minimum, non négligeable, critique et maximum) en relation avec des observations de coliformes de plus en plus fréquentes sur le réseau.

Il a aussi été possible de définir un taux de chlore à appliquer sur un site afin de diminuer le niveau de contamination bactérienne de l'eau et par conséquent réduire le risque d'apparition des coliformes sur ce site.

La mesure du CODB : un index du potentiel de reviviscence bactérienne des eaux

La mesure de la matière organique biodégradable dans l'eau est déterminée à partir de tests biologiques qui reposent sur deux concepts.

Le premier est basé sur le suivi de la croissance de souches pures ou d'une population bactérienne mixte dans un échantillon d'eau. Le maximum de croissance obtenu est converti en Carbone Organique facilement Assimilable (COA) et exprimé en µg de C eq. acétate/l en tenant compte du rendement de croissance de ces bactéries dans des solutions d'acétate de sodium.

Le second repose sur le suivi de la décroissance du Carbone Organique Dissous (COD) dans un échantillon d'eau ensemencé par une flore bactérienne indigène des eaux (flore en suspension ou flore fixée sur des particules de sable). La matière organique biadégradée est exprimée sous forme de Carbone Organique Dissous Biodégradable (CODB).

Des essais ont été réalisés sur différents types d'eau (eaux de rivière de la Seine, de l'Oise et de la Marne, eaux en cours de traitement de.potabilisation, eaux distribuées et eaux distillées) afin de mettre en évidence la relation existant entre la mesure du CODB en présence de bactéries fixées sur du sable et le maximum de croissance bactérienne enregistré dans les mêmes échantillons stérilisés puis réensemencés par des souches pures (Pseudomonas fluorescens P17, Pseudomonas fluorescens P17 + Spirillum NOX) ou par un inoculum mixte de bactéries indigènes de l'eau.

Les résultats de cette étude mettent en évidence :

- une relation entre le CODB et le maximum de croissance (Pseudomonas fluorescens P17) médiocre (r = 0,716 ; n = 28) pour des échantillons d'eau ensemencés par Pseudomonas fluorescens P17 seul (dénombrement en gélose);

- une relation entre le CODB et le maximum de croissance (Pseudomonas fluorescens P17) améliorée (r = 0,850, n = 31) pour des échantillons ensemencés simultanément avec un mélange de Pseudomonas fluorescens P17 et Spirillum NOX (dénombrement en gélose);

- une relation entre le CODB et le maximum de croissance (Spirillum NOX) très faible (r = 0,264 n = 31; corrélation non significative) pour des échantillons ensemencés simultanément avec un mélange de P17 + NOX (dénombrement en gélose);- le coefficient de corrélation entre le CODB et le COA (Pseudomonas fluorescens P17 + Spirillum NOX) est de 0.769 (n = 31) avec une équivalence de 140 µg de COA (eq. acétate) par mg de CODE lorsque P17 est utilisé isolément et 90 µg de COA (eq. acétate) par mg de CODB lorsque P17 et NOX sont utilisés simultanément;

- la relation entre le CODB et le maximum de croissance (flore naturelle mixte) est par contre très satisfaisante (r = 0,943; e = 30) lorsque les dénombrements bactériens sont effectués par microscopie en épifluorescence (coloration à l'acridine orange).

Le rendement de croissance est alors de 1,7.109 cellules pour 1 mg de CODB mesuré en présence de sable biologique.

En conclusion, la mesure du CODB au moyen de bactéries fixées, originellement décrite pour évaluer l'efficacité des filières de traitement de potabilisation vis-à-vis de l'élimination de la Matière Organique Biodégradable permet aussi de prédire le potentiel de recroissance bactérienne (bactéries indigènes) de différents types d'eau.

Interaction of cations, anions, and weak base quinine with rat renal cation transporter rOCT2 compared with rOCT1

The rat organic cation transporter (rOCT)-2 was characterized by electrical and tracer flux measurements compared with rOCT1. By applying choline gradients to voltage-clamped Xenopus oocytes expressing rOCT2, potential-dependent currents could be induced in both directions. Tracer flux measurements with seven organic cations revealed similar Michaelis-Menten constant values for both transporters, with the exception of guanidine. In parallel experiments with rOCT2 and rOCT1, inhibition of tetraethylammonium transport by 12 cations, 2 weak bases, corticosterone, and the anions para-amminohippurate, alpha-ketoglutarate, and probenecid was characterized. The IC(50) values of many inhibitors were similar for both transporters, whereas others were significantly different. Mepiperphenidol and O-methylisoprenaline showed an approximately 70-fold lower and corticosterone a 38-fold higher affinity for rOCT2. With the use of these inhibitors together with previous information on cation transporters, experimental protocols are proposed to dissect out the individual contributions of rOCT2 and rOCT1 in intact proximal tubule preparations. Inhibition experiments at different pH levels strongly suggest that the weak base quinine passively permeates the plasma membrane at physiological pH and inhibits rOCT2 from the intracellular side.

Detection of Aeromonas hydrophila in a drinking-water distribution system: a field and pilot study

A 16-month study was conducted on the presence of Aeromonas hydrophila in drinking water in Indiana, U.S.A. Enumeration was conducted in source water, in various sites within a water treatment plant, and in the distribution system in both bulk water and biofilm, as well as in a simulated (annular reactors) drinking-water distribution system. Presumptive Aeromonas spp. counts on source waters regularly approached 10(3)-10(4) CFU/100 mL, during summer months and granular activated carbon - filtered water counts ranged from <1 to 490 CFU/100 mL. In source water, presumptive Aeromonas levels were related to water temperature. Aeromonas hydrophila was never detected in the treatment plant effluent or distributed bulk water, showing disinfectant efficiency on suspended bacteria; however, isolates of A. hydrophila were identified in 7.7% of the biofilm samples, indicating a potential for regrowth and contamination of drinking-water distribution systems.

Localization of organic cation transporters OCT1 and OCT2 in rat kidney

Renal excretion and reabsorption of organic cations are mediated by electrogenic and electroneutral organic cation transporters, which belong to a recently discovered family of polyspecific transporters. These transporters are electrogenic and exhibit differences in substrate specificity. In rat, the renal expression of the polyspecific cation transporters rOCT1 and rOCT2 was investigated. By in situ hybridization, significant amounts of both rOCT1 and rOCT2 mRNA were detected in S1, S2, and S3 segments of proximal tubules. By immunohistochemistry, expression of the rOCT1 protein was mainly observed in S1 and S2 segments of proximal tubules, with lower expression levels in the S3 segments. At variance, rOCT2 protein was mainly expressed in the S2 and S3 segments. Both transporters were localized to the basolateral cell membrane. Neither rOCT1 nor rOCT2 was detected in the vasculature, the glomeruli, and nephron segments other than proximal tubules. The data suggest that rOCT1 and rOCT2 are responsible for basolateral cation uptake in the proximal tubule, which represents the first step in cation secretion.

Selectivity of the polyspecific cation transporter rOCT1 is changed by mutation of aspartate 475 to glutamate

After site-directed mutagenesis, the organic cation transporter rOCT1 was expressed in Xenopus laevis oocytes or human embryonic kidney cells and functionally characterized. rOCT1 belongs to a new family of polyspecific transporters that includes transporters for organic cations and anions and the Na(+)-carnitine cotransporter. When glutamate was substituted for Asp475 (middle of the proposed 11th transmembrane alpha-helix), the V(max) values for choline, tetraethylammonium (TEA), N(1)-methylnicotinamide, and 1-methyl-4-phenylpyridinium were reduced by 89 to 98%. The apparent K(m) values were also decreased (choline by 15-fold, TEA by 8-fold, N(1)-methylnicotinamide by 4-fold) or remained constant (1-methyl-4-phenylpyridinium). After the mutation, the membrane potential dependence of the K(m) value for [(3)H]choline uptake was abolished. The affinity of n-tetraalkyl ammonium compounds to inhibit TEA uptake was increased. This affinity and its increase by the D475E mutation were increased with the length of the n-alkyl chains. After expression in X. laevis oocytes, the IC(50) ratios of wild-type and D475E mutant were 1.7 (tetramethylammonium), 4.3 (TEA), 5.0 (tetrapropylammonium), 5.0 (tetrabutylammonium), and 65 (tetrapentylammonium). Cationic inhibitors with ring structures were differentially affected: the IC(50) value for TEA inhibition by cyanine 863 remained unchanged, whereas it was increased for quinine. The data suggest that rOCT1 contains a large cation-binding pocket with several interaction domains that may be responsible for high-affinity binding of structurally different cations and that Asp475 is located close to one of these interaction domains.

Human neurons express the polyspecific cation transporter hOCT2, which translocates monoamine neurotransmitters, amantadine, and memantine

Recently, we cloned the human cation transporter hOCT2, a member of a new family of polyspecific transporters from kidney, and demonstrated electrogenic uptake of tetraethylammonium, choline, N1-methylnicotinamide, and 1-methyl-4-phenylpyridinium. Using polymerase chain reaction amplification, cDNA sequencing, in situ hybridization, and immunohistochemistry, we now show that hOCT2 message and protein are expressed in neurons of the cerebral cortex and in various subcortical nuclei. In Xenopus laevis oocytes expressing hOCT2, electrogenic transport of norepinephrine, histamine, dopamine, serotonin, and the antiparkinsonian drugs memantine and amantadine was demonstrated by tracer influx, tracer efflux, electrical measurements, or a combination. Apparent Km values of 1.9 +/- 0.6 mM (norepinephrine), 1.3 +/- 0.3 mM (histamine), 0.39 +/- 0.16 mM (dopamine), 80 +/- 20 microM (serotonin), 34 +/- 5 microM (memantine), and 27 +/- 3 microM (amantadine) were estimated. Measurement of trans-effects in depolarized oocytes and human embryonic kidney cells expressing hOCT2 suggests that there were different rates and specificities for cation influx and efflux. The hypothesis is raised that hOCT2 plays a physiological role in the central nervous system by regulating interstitial concentrations of monoamine neurotransmitters that have evaded high affinity uptake mechanisms. We show that amantadine does not interact with the expressed human Na+/Cl- dopamine cotransporter. However, concentrations of amantadine that are effective for the treatment of Parkinson's disease may increase the interstitial concentrations of dopamine and other aminergic neurotransmitters by competitive inhibition of hOCT2.

A proton-translocating H+-ATPase is involved in C6 glial pH regulation

Glial cells extrude acid equivalents to maintain pHi. Although four mechanisms have been described so far, pHi-control under physiological conditions is still not sufficiently explained. We therefore investigated whether a H+-translocating ATPase is involved in glial pHi homeostasis using an established glial cell line (C6 glioma). In the absence of bicarbonate, the inhibition of H+-ATPases by NEM led to a pHi decrease. The application of a more specific inhibitor (NBD-Cl) showed that the H+-ATPase involved is of the vacuolar type. Inhibition went along with delayed cell swelling. Together with the fact that glial acidification was far more pronounced in Na+-free media, this may serve as evidence for a secondary activation of Na+/H+-exchange once an activation setpoint is reached, which in turn causes secondary swelling from Na+-uptake. Stimulation of Na+/H+-exchange by PMA can increase the setpoint. pHi-recovery after an acid load was blocked by the inhibition of v-type H+-ATPase, if pHi did not reach 6.6 during the acid load. The inhibition of Na+/H+-exchange by amiloride inhibited recovery only if acidification was below the threshold. Finally, in bicarbonate-free media a v-type H+-ATPase contributes to pH-regulation in glial cells, especially during pH-homeostasis at physiological conditions, while Na+/H+-exchange gains significance during severe acid loads.

Transport of the new chemotherapeutic agent beta-D-glucosylisophosphoramide mustard (D-19575) into tumor cells is mediated by the Na+-D-glucose cotransporter SAAT1

For beta-D-glucosylisophosphoramide mustard (beta-D-Glc-IPM), a new alkylating drug in which isophosphoramide mustard is stabilized, a higher selectivity and lower myelotoxicity was observed than for the currently used cytostatic ifosfamide. Because beta-D-Glc-IPM is hydrophilic and does not diffuse passively through the lipid bilayer, we investigated whether a transporter may be involved in the cellular uptake. A variety of cloned Na+-sugar cotransporters were expressed in Xenopus oocytes, and uptake measurements were performed. By tracer uptake and electrical measurements it was found that beta-D-Glc-IPM was transported by the low-affinity Na+-D-glucose cotransporter SAAT1, which had been cloned from pig and is also expressed in humans. At membrane potentials between -50 and -150 mV, a 10-fold higher substrate affinity (Km approximately 0.25 mM) and a 10-fold lower Vmax value were estimated for beta-D-Glc-IPM transport than for the transport of D-glucose or methyl-alpha-D-glucopyranoside (AMG). Transport of beta-D-Glc-IPM and glucose by SAAT1 is apparently performed by the same mechanism because similar sodium dependence, dependence on membrane potential, electrogenicity, and phlorizin inhibition were determined for beta-D-Glc-IPM, D-glucose, and AMG. Transcription of human SAAT1 was demonstrated in various human carcinomas and tumor cell lines. In one of these, the human carcinoma cell line T84, phlorizin inhibitable uptake of beta-D-Glc-IPM was demonstrated with substrate saturation and an apparent Km of 0.4 mM. The data suggest that the Na+-D-glucose cotransporter SAAT1 transports beta-D-Glc-IPM into human tumor cells and may accumulate the drug in the cells. They provide an example for drug targeting by employing a plasma membrane transporter.

A reevaluation of substrate specificity of the rat cation transporter rOCT1

The substrate specificity of the previously cloned rat cation transporter rOCT1, which is expressed in kidney, liver, and small intestine, was reevaluated. rOCT1 is the first member of a new protein family comprising electrogenic and polyspecific cation transporters that transport hydrophilic cations like tetraethylammonium, choline, and monoamine neurotransmitters. Previous electrical measurements suggested that cations like quinine, quinidine, and cyanine 863, which have been classified as type 2 cations in the liver, are also transported by rOCT1, since they may induce inward currents in rOCT1 expressing Xenopus oocytes (Busch, A. E., Quester, S., Ulzheimer, J. C., Waldegger, S., Gorboulev, V., Arndt, P., Lang, F., and Koepsell, H. (1996) J. Biol. Chem. 271, 32599-32604). Tracer flux measurements with oocytes and with stably transfected human embryonic kidney cells showed that [3H]quinine and [3H]quinidine are not transported by rOCT1. The voltage dependence observed for the quinine- or quinidine-induced inward currents in rOCT1-expressing oocytes, and tracer efflux measurements indicate that the inward currents by type 2 cations are generated by the inhibition of electrogenic efflux of transported type 1 cations. Therefore, rOCT1 cannot contribute to transport of type 2 cations in the liver and the hepatic transporter for type 2 cations remains to be identified.

Inhibition of lactate export by quercetin acidifies rat glial cells in vitro

The relationship between glial lactate release and glial intracellular pH (pHi) regulation is studied using C6 glioma cells and rat astrocytes in vitro, and the lactate transport inhibitors quercetin and alpha-cyano-4-hydroxycinnamate (CHC). pHi is measured using 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). The results show that lactate release is mediated partly by a specific lactate transport system inhibitable by quercetin (50 microM), but not by CHC (5 mM). Inhibition by quercetin results in a significant 3-4-fold increase of intracellular lactate and a decrease of intracellular pH to 6.9. A participation of quercetin-inhibitable lactate transport in glial pHi-regulation is suggested by the observation that pHi-homeostasis after acidification by diffusion of undissociated lactic acid into the cell is inhibited by quercetin. The existence of a system controlling lactate release in glial cells may also reflect a function of astrocytes to supply neurons with lactate.

[Impairment of myocardial perfusion reserve in microvascular angina (syndrome X): assessment by 99mTc-MIBI-SPECT]

AIM

In 22 patients with typical chest pain and normal coronary arteries (microvascular angina, syndrome X) 99mTc-MIBI-SPECT was examined in regard to assess impairment of myocardial perfusion reserve.

METHOD

The study was performed with 99mTc-MIBI-SPECT at rest and under vasodilation with dipyridamole. The findings were compared with a normal database. A normal perfusion reserve was said to be an increase > 20% of the 99mTc-MIBI-activity.

RESULTS

In 2/22 (9%) of the patients the perfusion reserve lay > 20% i.e. 37%. In 91% of the patients a diminution or even decrease of the perfusion was to be seen. From these 9/22 (41%) of the patients showed a diminution of the 99mTc-MIBI-uptake by 6%. 1/22 patients had a decrease of the perfusion under vasodilation with dipyridamole i.e. a lower activity of 99mTc-MIBI by 13%

CONCLUSION

Vasodilation 99mTc-MIBI-SPECT offers good imaging quality and enables semi-quantitative assessment of myocardial perfusion reserve in patients with microvascular angina.

[Diastolic left ventricular dysfunction with microvascular angina (Syndrome X)]

Findings on left ventricular function in microvascular angina (syndrome X) are somewhat controversial. Recently, an increased prevalence of insulin resistance and hyperlipoproteinemia has been demonstrated as well as arterial hypertension potentially impairing the left ventricular diastolic function. In an attempt to analyze the diastolic function at rest, we investigated by Doppler echocardiography the transmitral blood flow in 16 patients (51 +/- 8 years). The diastolic data were compared with those of 12 healthy people (50 +/- 6 years) who were matched for age. The patients with microvascular angina revealed a slightly higher systolic blood pressure (134 +/- 18 mm Hg vs 125 +/- 9 mm Hg, n.s.), but imposed by higher left ventricular mass index (92 +/- 18 g/m2 vs 65 +/- 13 g/m2, p < 0.001). There was a trend to an elevated A-wave-peak during transmitral blood flow (61 +/- 14 cm/s vs 50 +/- 9 cm/s). The findings suggest impairment of the left ventricular relaxation before manifestation of left ventricular hypertrophy and hypertension takes place.

Insulin resistance and hyperlipoproteinemia in microvascular angina: risk factors or pathogenetic link?

BACKGROUND

Patients with chest pain and normal epicardial coronary arteries (microvascular angina; syndrome X) are characterized by an impairment of myocardial perfusion reserve which may be related to functional and morphological abnormalities of the intramyocardial arterioles.

METHODS

In an attempt to identify predisposing factors for microvascular angina we investigated 34 consecutive patients (15 female, 19 male; mean age 53 +/- 7 years) with microvascular angina but without hypertension or left ventricular hypertrophy. The metabolic profile, including plasma insulin, glucose, cholesterol, low-density lipoprotein cholesterol, triglycerides, very-low-density lipoprotein cholesterol and fibrinogen levels, was determined in each case. Furthermore, insulin and glucose levels were measured after an oral glucose load of 100 g over 3 h. All parameters were compared with those of a control group of 15 healthy subjects matched for age, sex and body mass index.

RESULTS

The systolic blood pressure in microvascular angina was 137 +/- 17 mmHg and thus higher than that of healthy controls (124 +/- 11 mmHg); diastolic blood pressure was 85 +/- 7 compared with 78 +/- 9 mmHg in controls. Insulin level was significantly elevated in patients with microvascular angina 90 min (median: 101 versus 54 microU/ml) and 120 min (median: 88 versus 51 microU/ml) after ingestion of 100 g glucose. The fasting glucose level was 98 +/- 12 versus 87 +/- 7 mg/dl in controls. Glucose concentration was also elevated after 30 min (176 +/- 28 versus 148 +/- 32 mg/dl), after 45 min (198 +/- 35 versus 152 +/- 53 mg/dl) and after 60 min (193 +/- 44 versus 145 +/- 54 mg/dl). In microvascular angina, parameters such as total cholesterol (244 +/- 46 versus 199 +/- 29 mg/dl), low-density lipoprotein cholesterol (157 +/- 41 versus 122 +/- 18 mg/dl) and fibrinogen (377 +/- 150 versus 285 +/- 69 mg/dl) were elevated.

CONCLUSIONS

The metabolic profile in patients with microvascular angina suggests a pathogenetic role of insulin resistance and hyperlipoproteinemia in the setting of impaired myocardial coronary reserve and in early stages of hypertensive heart disease.

[The significance of insulin resistance and hyperlipidemia in microvascular angina (syndrome X)]

Patients with chest pain and normal epicardial coronary arteries are characterized by an impairment of myocardial perfusion reserve. Functional and morphological abnormalities of the intramyocardial arterioles are suggested to be responsible for this, possibly as a consequence of hypertension and/or left ventricular hypertrophy. In an attempt to isolate predisposing factors of microvascular angina we investigated 34 patients (15 f, 19 m) with a mean age of 53 +/- 7 years. They were diagnosed as microvascular angina without hypertension or left ventricular hypertrophy. Parameters such as plasma insulin, glucose, cholesterol, LDL-cholesterol, triglycerides, (VLDL-cholesterol) and fibrinogen were determined for a metabolic profile. Furthermore, insulin and glucose were measured after an oral glucose load of 100 g glucose (OGTT) over 3 h. All parameters were compared to a control group of 15 healthy people matched for age and body mass index. In the study population systolic blood pressure was within normal limits at 137 +/- 17 mm Hg and thus higher than control at 124 +/- 11 mm Hg (p < 0.02). Furthermore, diastolic blood pressure was 85 +/- 7 mm Hg compared to 78 +/- 9 mm Hg in controls (p < 0.02). Insulin was significantly elevated in patients with microvascular angina 90 min (median: 101 vs 54 microU/ml; p < 0.01) and 120 min (median: 88 vs 51 microU/ml; p < 0.05) after ingestion of 100 g glucose. The fasting glucose was elevated at 98 +/- 12 compared to 87 +/- 7 mg/dl in controls (p < 0.01). Glucose concentration was also elevated after 30 min at 176 +/- 28 compared to 148 +/- 32 mg/dl (p < 0.02), after 45 minutes (198 +/- 35 compared to 152 +/- 53 mg/dl) (p < 0.01) and 60 minutes (193 +/- 44 compared to 145 +/- 54 mg/dl) (p < 0.01). In microvascular angina parameters such as total cholesterol: (244 +/- 46 vs 199 +/- 29 mg/dl (p < 0.01)), LDL-cholesterol (157 +/- 41 vs 122 +/- 18 mg/dl (p < 0.01)) and fibrinogen: (377 +/- 150 vs to 285 +/- 69 mg/dl (p < 0.03)) were elevated. These findings suggest a pathogenetic role of insulin resistance, hyperlipoproteinemia and elevated levels of fibrinogen for impaired myocardial coronary reserve. This metabolic constellation as well as exhaustion of coronary reserve is often found in hypertensive patients and may identify microvascular angina as an early stage of hypertensive heart disease before manifest hypertension has developed.

Neuron-glial interaction during injury and edema of the CNS

During injury and ischemia of the CNS mediator compounds are released or activated which cause secondary swelling and damage of nerve cells. Such mediators are glutamate, acidosis, free fatty acids, or high extracellular potassium. Glial homeostatic mechanisms are activated to prevent the secondary injury from these mediators. The glial clearance mechanisms have been studied in detail using in vitro systems allowing for a close control of the glial environment. Current evidence suggests glial swelling to occur together with glutamate uptake or in response to extracellular acidosis. Glial swelling, therefore, is rather the result of homeostatic mechanisms than an indication of glial demise.

Abnormal expression of neurofilament proteins in Ewing's sarcoma cell cultures

A neural origin of Ewing's sarcoma (ES) has often been suggested and we have demonstrated neurofilament protein expression in ES cells. However, only the 200-kD subunit has been revealed in all of the ES cells analyzed. The 160- and 68-kD subunits were always absent. For these reasons, we have attempted to induce neural differentiation in 3 ES cell lines with different types of inducers: tetradecanoylphorbol-13-acetate (TPA) retinoic acid and nerve growth factor. When the cell lines were cultured for 7 days with TPA (10(-9) M) or retinoic acid (10(-7) M), only the 68-kD neurofilament subunit was slightly induced. No inducation was obtained when nerve growth factor was used, even at a 21-day culture. These results are in agreement with the putative neural origin of ES and may indicate an abnormal expression of neurofilament proteins in this tumor.

Association of breakpoint 14q23 with uterine leiomyoma

A chromosomal study of short-term cultured tumor cells from a benign uterine leiomyoma showed a clonal insertion, dir ins(14;6)(q23;p23p25) as a unique change. This finding supports the hypothesis of a specific association of the breakpoint 14q23 with uterine leiomyoma.

Chromosomes in Ewing's sarcoma. I. An evaluation of 85 cases of remarkable consistency of t(11;22)(q24;q12)

Since our initial reports on chromosomal studies in eight Ewing's sarcomas (ES), we have carried out similar investigations on 23 additional ES specimens following short-term culture of tumor cells (16 cases), and established in vitro cell lines (three cases) and on xenografted tumors in nude mice (four cases). We demonstrated the presence of the reciprocal t(11;22)(q24;q12) in every case except one that exhibited a complex t(11;22;14)(q24;q12;q11). On the basis of results from these additional 23 cases, we confirm the consistency of the t(11;22)(q24;q12) in ES. Moreover, we reviewed 54 ES cases reported by other investigators; when added to our 31 cases, this brings the total number to 85 unrelated cases of ES available for an evaluation of the frequency of involvement of bands 11q24 and 22q12 in translocations in ES. The standard t(11;22)(q24;q12) proved to be a remarkably consistent event, present in 83% of the cases. Five percent of the cases exhibited complex translocations involving a third chromosome in addition to chromosomes #11 and #22. In 4% of the cases variant translocations involved 22q12 but with a chromosome(s) other than #11. The breakpoint on chromosome 22q12 appears to be the most consistently observed event in 92% of the cases, whereas, the breakpoint at chromosome 11q24 was observed in 88% of the cases.