Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5082-5087 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recent experiments on the static and dynamic properties of polycrystalline colloidal solids show a pronounced influence of morphological details. Here we investigate several possibilities to vary systematically one key morphological parameter, namely the average crystallite radius rc of polycrystalline solids. We report measurements of rc as observed by microscopy in well-characterized Yukawa model suspensions. The pair energy of interaction is systematically varied through precise experimental adjustment of the suspension parameters packing fraction Φ, number of ionic surface groups N, and concentration of screening ions c. The average size is found to systematically decrease with increasing interaction. At fixed suspension parameters we performed solidification under shear, i.e., in the presence of alternating electric fields. We report preliminary results in dependence on both the electric field strength and frequency. The grain size increases with increasing shear rates. It shows a complex behavior as a function of the frequency and the wave form of the applied field. Qualitative explanations are discussed and a first application is presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: A voltage-gated K+ channel protein has been cloned from a cDNA library derived from poly(A)+ RNA of the rat pituitary tumour cell line GH3/B6 by the polymerase chain reaction technique. The clone referred to as RGHK9 encodes a protein sequence very similar to a recently cloned K+ channel protein from rat brain and heart, with deviations in a few amino-acid positions. In situ hybridization experiments show that RGHK9 mRNA is also present in the anterior pituitary as well as in other brain regions and that it is particularly abundant in the hippocampus. After injection of cRNA transcribed from the RGHK9 cDNA clone into Xenopus oocytes, the expressed protein induces a transient K+ current. Except for the activation kinetics the properties of this current are indistinguishable from that of the native transient K+ current measured in GH3/B6 cells, e.g. both K+ currents are blocked by 4-aminopyridine and show the same voltage dependence and slope of steady state activation and inactivation as well as identical time constants of, and slow recovery from, inactivation. Taken together, these data show that the outward-rectifying voltage-gated K+ channel protein encoded by the RGHK9 cDNA correlates well in its functional properties with that of a very similar, if not identical, K+ channel present in GH3/B6 cells.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 1 (1989), S. 0 
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Protein kinase C was activated in Xenopus laevis oocytes by phorbol ester treatment and its effects on the inositol trisphosphate/Ca2+ transmembrane signalling pathway analysed. Induction of the pathway was achieved by ligand stimulation of TRH receptors translated from GH3 pituitary cell mRNA. In voltage-clamped oocytes bath application of peptide, injection of guanosine 5′-(3-O-thio) triphosphate (GTPγS), inositol trisphosphate or Ca2+ all elicited inward membrane currents. Treatment of oocytes with tumour-promoting phorbol esters for 35 min almost completely abolished the ligand and GTPγS-induced responses. In contrast, phorbol ester treatment enhanced inositol trisphosphate-generated membrane currents. Ca2+-mediated responses remained unaffected by tumour promoters. The data indicate a dual role for protein kinase C in the modulation of transmembrane signalling: a feedback mechanism prevents phosphoinositide turnover whereas a feedforward reaction triggers the effect of intracellular inositol trisphosphate on the Ca2+ release.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. A system of coupled bistable Hopf oscillators with an external periodic input source was used to model the ability of interacting neural populations to synchronize and desynchronize in response to variations of the input signal. We propose that, in biological systems, the settings of internal and external coupling strengths will affect the behaviour of the system to a greater degree than the input frequency. While input frequency and coupling strength were varied, the spatio-temporal dynamics of the network was examined by the bi-orthogonal decomposition technique. Within this method, effects of variation of input frequency and coupling strength were analyzed in terms of global, spatial and temporal mode entropy and energy, using the spatio-temporal data of the system. We observed a discontinuous evolution of spatio-temporal patterns depending sensitively on both the input frequency and the internal and external coupling strengths of the network.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 409 (1987), S. 569-577 
    ISSN: 1432-2013
    Keywords: Node of Ranvier ; Rat nerve ; Na current ; Action potential ; Body temperature ; Temperature dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract (1) Action potentials and membrane currents were recorded in single myelinated rat nerve fibres at 20 and 37° C. Three experiments were also performed in single cat nerve fibres. (2) K currents were blocked by internal CsCl and external TEA. The steady state and kinetic parameters of Na activation and inactivation were determined at both temperatures. (3) When the temperature was raised from 20 to 37° C, steady state Na activation,m ∞(V), and inactivation,h ∞(V), did not change significantly. (4) The time constant of Na activation, τm, was determined within the potential range of −40 to 125 mV at 20° C andV=40–60 mV at 37° C. The temperature coefficient, Q10, of τm was 2.2. (5) The decay in the Na current was described by two exponentials at both temperatures. The amplitude of the slow phase was 1–10%. The time constant of the fast phase of Na inactivation, τh1, was determined at both temperatures within the potential range of −50 mV to 125 mV. The Q10 of τh1 was 2.9 and did not depend on potential. (6) The Na equilibrium potential was 152 mV at 20° C and 144 mV at 37° C. The leakage conductance was 24 nS at 20° C and 43 nS at 37° C. These differences were interpreted as signs of fibre deterioration at higher temperature. (7) The results from the current and voltage clamp experiments performed in the cat nerve were essentially the same as those in the rat nerve fibres. (8) The action potentials computed on the basis of the voltage clamp results at 20° C were similar to the ones actually measured. This was also true for those action potentials predicted for 37° C on the basis of the 20° C data, theg L andV Na values measured at 37° C, and the Q10 values of the time constants. (9) Steady state values and kinetic parameters of K permeability were adopted from the literature. As in the experiments the influence ofP K on the shape of the predicted action potential was almost negligible at both temperatures.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 330 (1971), S. 61-73 
    ISSN: 1432-2013
    Keywords: Potassium Inactivation ; Voltage Clamp ; Ranvier Node
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Voltage clamp measurements were performed on single myelinated nerve fibres of the frog Xenopus laevis. 2. During long-lasting depolarizations the potassium current decayed in a fast phase with a time constant of about 0.6 sec and a following slow phase with a time constant between 3.6 (V=0) and 20 sec (V=100 mV). 3. The decay of the potassium current was the result of an inactivation of the potassium permeability and not of a shift of the potassium equilibrium potential as shown by experiments in isotonic KCl solution. 4. At a hyperpolarization of −20 mV the potassium inactivation was fully removed. It remained incomplete even at large depolarizations. The steady-state inactivation curve was S-shaped but not symmetrical. 5. The experimental results could be described by extending the Hodgkin-Huxley equations introducing two terms of potassium inactivation.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 406 (1986), S. 397-404 
    ISSN: 1432-2013
    Keywords: Node of Ranvier ; Rat nerve ; Na current ; Temperature dependence ; Voltage clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1) Voltage clamp experiments were performed in single myelinated nerve fibres of the rat and the effect of temperature on Na currents was investigated between 0°C and 40°C. 2) The amplitude of the peak Na current changed with aQ 10=1.1 between 40° and 20°C and with aQ 10=1.3 between 20° and 10°C. Below 10°C the peak Na current changed with aQ 10=1.9. 3) The temperature coefficient for time-to-peak (tp), the measure for Na activation, and τh1 and τh2, the time constants for Na inactivation changed throughout the temperature range.Q 10 for all of these kinetic parameters increased from 1.8–2.1 between 40° and 20°C to 2.6–2.7 between 20° and 10°C. Below 10°CQ 10 increased to 3.7 for τh1 and tp, and to 2.9 for τh2. When the series resistance artifacts were minimized by addition of 6 nM TTX, theQ 10's atT〈10°C were 2.9–3.0. 4) When the temperature was decreased from 20° to 0°C, both the curve relating Na permeability to potential,P Na(V), and the steady state Na inactivation curve,h∞(V), were reversibly shifted towards more negative potentials by 6 mV and 11 mV, respectively. When the temperature was increased from 20° to 37°C no shifts occurred. 5) The Hodgkin-Huxley rate constants αh(V) and βh(V) were calculated fromh ∞(V) and τh (or τh1) at 20° and 4°C. The shift inh∞(V) and the change inh ∞(V), which occurred within this temperature range, could be described assuming a selective shift in τh(V) along the potential axis.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of neurology 218 (1978), S. 179-186 
    ISSN: 1432-1459
    Keywords: EEG, sleep deprivation ; Sleep deprivation, EEG ; Short sleep EEG ; Seizures cerebral
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Es wurden 185 EEGs nach 24h Schlafentzug ausgewertet. Hiervon enthielten 110 EEGs (59%) diagnostisch weiterführende Befunde. In 24% fand sich Krampfaktivität. Es wurden die Dauer der Schlafstadien, die Häufigkeit des Auftretens von Krampfaktivität, paroxysmalen Steilwellengruppen und Lokalbefunden analysiert. Die Schlaftiefen A bis C (nach Loomis) wurden während einer EEG-Ableitung von 30–40 min gleichmäßig lang, Stadium D nur kurz, Stadium E nicht erreicht. Pathologische EEG-Befunde traten überwiegend in den Schlafstadien A und B auf. Lokalbefunde fanden sich besonders im Stadium C. Zwischen den Patientengruppen mit primär generalisierten Anfällen, psychomotorischen Anfällen sowie Zuständen ungeklärter Bewußtseinsstörung fand sich kein signifikanter Unterschied hinsichtlich Auftreten und Ausprägung der EEG-Veränderungen. Die regelmäßig durchgeführte Hyperventilation und Fotostimulation und die Flüssigkeitsbelastung, die nur bei negativen Vorbefunden zusätzlich durchgeführt wurde, ergaben zusammen in 50% eine neue Information.
    Notes: Summary One hundred and eighty-five EEGs recorded after deprivation of sleep for 24h were evaluated. Valuable diagnostic information was found in 59% of the EEG recordings; 24% of the EEGs contained seizure activity. The duration of the stages of sleep and the frequency of seizure activity, paroxysmal sharp wave groups and localizing findings were analyzed. The sleep stages A to C (based on the Loomis scale) were reached for about equal duration by an EEG recording of 30–40 min; sleep stage D was reached only shortly and stage E was not observed. Pathological EEG findings appeared for the most part in the sleep stages A and B. Localized findings were pronounced in stage C. No significant differences pertaining to the occurrence and form of EEG patterns were found between patient groups with primary generalized seizures, psychomotor seizures or those with unclarified disturbances of consciousness. The combination of the short sleep EEG following 24h of sleep deprivation with subsequent use of the additional provocative methods of hyperventilation, photostimulation and hydration, yielded, in all, new information in 50% of the patients. Each of these additional methods contributed nearly equally to this information.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1432-2013
    Keywords: Key words Inward rectifier ; K+ current ; Endogenous ion channels ; Oocytes of Xenopus laevis ; Voltage clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  An endogenous inward-rectifying K+ current is described, which is present in native oocytes of some Xenopus laevis donors. Experiments were performed using defolliculated oocytes from donor frogs obtained from two different suppliers. In all oocytes from animals from one source, an inward-rectifying K+ current could be elicited with negative pulses from a holding potential of –20 mV in external solutions with a high K+ concentration. Increasing external K+ concentrations increased the amplitude of this current and shifted the reversal potential towards more positive potentials. In 118 mM KCl, the inward-rectifying K+ current partially inactivated between –20 and –80 mV and completely inactivated at more negative membrane potentials; 50% steady-state inactivation occurred near –50 mV. The time course of inactivation of the inward-rectifying current could be well fitted with two exponentials. The slow time constant had values of about 500 ms and was voltage independent. In contrast, the fast time constant and the time to reach the peak inward current decreased with more negative membrane potentials. Ba2+, Cs+, quinine (all 5 mM) and 50 mM tetraethylammonium partially blocked the inward-rectifying K+ current, whereas 10 mM 4-aminopyridine was without blocking effect. The oxidant chloramine-T blocked the inward-rectifying K+ current without slowing its inactivation.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 430 (1995), S. 283-292 
    ISSN: 1432-2013
    Keywords: Myelinated nerve fibre ; Action potential ; Voltage clamp ; Sodium current ; Potassium currents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Action potentials and membrane currents were recorded in single human myelinated nerve fibres under current- and voltage-clamp conditions at room temperature. Nerve material was obtained from patients undergoing nerve graft operations. Successful recordings were made in 11 nerve fibres. In Ringer's solution, large transient Na currents were recorded, which could be blocked completely with tetrodotoxin. Partial block of these currents with 3 nM tetrodotoxin was used to reduce the voltage-clamp error due to series resistance. Outward K currents were very small in intact nerve fibres, but had a large amplitude in fibres showing signs of paranodal demyelination. In isotonic KCl, the K current could be separated into three components: two fast components (Kf1 and Kf2) and one slow component (Ks). Time constants and steady-state activation and inactivation of Na permeability and of fast and slow K conductance were measured within the potential range of −145 mV to +115 mV. From these parameters, the corresponding rate constants were calculated and a mathematical model based on the Frankenhaeuser-Huxley equations was derived. Calculated action potentials closely matched those recorded. Single calculated action potentials were little affected by removing the fast or slow K conductance, but the slow K conductance was required to limit the repetitive response of the model to prolonged stimulating currents.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...