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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 23 (1984), S. 6216-6221 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 59 (1981), S. 281-285 
    ISSN: 1432-1440
    Keywords: Long Q-T syndrome ; Ventricular arrhythmia ; Sudden death ; Stellectomy ; QT-Syndrom ; Ventrikuläre Rhythmusstörungen ; Sekundenherztod ; Stellektomie
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Es wird über den Fall eines latenten QT-Syndroms berichtet mit recidivierenden Attacken von Kammerflimmern ohne wesentliche QT-Verbreiterung im Elektrokardiogramm. Die Patientin war resistent gegen die üblichen Antiarrhythmika und mußte 99mal defibrilliert werden. Erst die Stellatum-Blockade mit anschließender Stellektomie führte zur Anfallsfreiheit über einen Zeitraum von jetzt 1 1/2 Jahren. Ähnlich wie beim klassischen QT-Syndrom ist deshalb bei recidivierendem Kammerflimmern die probatorische Stellatum-Blockade mit Injektion von Lidocain und bei Erfolg eine Stellektomie angezeigt, wenn Verdacht auf ein latentes QT-Syndrom besteht und andere Ursachen ausgeschlossen sind.
    Notes: Summary Case description of a 30 year-old woman with recurrent attacks of symptomatic ventricular tachyarrhythmias but without Q-T prolongation in the electrocardiogram. All conventional antiarrhythmic agents failed to suppress the arrhythmia and electrical defibrillation had to be carried out 99 times. Blockade of the left stellate ganglion with lidocaine followed by stellectomy led to successful control of the dangerous rhythm disturbance for a follow-up period of 1.5 years. As in patients with the classical long Q-T syndrome stellate ganglion blockade and stellectomy might be indicated in cases with the so called latent Q-T syndrome and life threatening ventricular arrhythmias resistant to antiarrhythmic agents.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 132 (1993), S. 211-227 
    ISSN: 1432-1424
    Keywords: (H,K)-ATPase ; gastric ; electrogenic ; Concentration jump ; caged ATP ; black lipid membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary (H,K)-ATPase containing membranes from hog stomach were attached to black lipid membranes. Currents induced by an ATP concentration jump were recorded and analyzed. A sum of three exponentials (τ 1 -1 ≈ 400 sec−1, τ 2 -1 ≈ 100 sec−1, τ 3 -1 ≈ 10 sec−1; T = 300 K, pH 6, MgCl2 3 mm, no K+) was fitted to the transient signal. The dependence of the resulting time constants and the peak current on electrolyte composition, ATP conversion rate, temperature, and membrane conductivity was recorded. The results are consistent with a reaction scheme similar to that proposed by Albers and Post for the NaK-ATPase. Based on this model the following assignments were made: τ 2 corresponds to ATP binding and exchange with caged ATP. τ 1 describes the phosphorylation reaction E1 · ATP → E1P. The third, slowest time constant τ 3 is tentatively assigned to the E1P → E2P transition. This is the first electrogenic step and is accelerated at high pH and by ATP via a low affinity binding site. The second electrogenic step is the transition from E2K to E1H. The E2K ↔ E1H equilibrium is influenced by potassium with an apparent K 0.5 of 3 mm and by the pH. Low pH and low potassium concentration stabilize the E1 conformation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1424
    Keywords: Lobster muscle ; Na/Ca exchanger ; Proteoliposomes ; Planar lipid bilayers ; Capacitive coupling ; Caged Ca2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The Na/Ca exchanger from lobster muscle crossreacts specifically with antibodies raised against the dog heart Na/Ca exchanger. Immunoblots of the lobster muscle and mammalian heart exchangers, following SDS-PAGE, indicate that the invertebrate and mammalian exchangers have similar molecular weights: about 120 kDa. The exchanger from lobster muscle was partially purified and functionally reconstituted into asolectin vesicles which were loaded with 160 mm NaCl. 45Ca uptake by these proteoliposomes was promoted by replacing 160 mm NaCl in the external medium with 160 mm KCl to produce an outwardly-directed Na+ concentration gradient. When the proteoliposomes were adsorbed onto black lipid membranes (BLM), and DMNitrophen-Ca2+ (“caged Ca2+”) was added to the KCl medium, photolytically-evoked Ca2+ concentration jumps elicited transient electric currents. These currents corresponded to positive charge exiting from the proteoliposomes, and were consistent with the Na/Ca exchanger-mediated exit of 3 Na+ in exchange for 1 entering Ca2+. The current was dependent upon the Ca2+ concentration jump, the protein integrity, and the outwardly directed Na+ gradient. KCl-loaded proteoliposomes did not produce any current. Low external Na+ concentrations augmented the current, whereas Na+ concentrations 〉25 mM reduced the current. The dependence of the current on free Ca2+ was Michaelis-Menten-like, with halfmaximal activation (KM(Ca)) at 〈10 μm Ca2+. Caged Sr2+ and Ba2+, but not Mg2+, also supported photolysisevoked outward current, as did Ni2+, but not Mn2+. However, Mg2+ and Mn2+ augmented the Cadependent current, perhaps by facilitating the adsorption of proteoliposomes to the BLM. The Ca-dependent current was irreversibly blocked by La3+ (added as 200 μm DMN-La3+). The results indicate that the properties of the Na/Ca exchanger can be studied with these electrophysiological methods.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 43 (1978), S. 317-333 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The noise behavior of lipid bilayer membranes, doped with a chemically dimerized gramicidin A, was investigated. In contrast to normal gramicidin A, which generates a Lorentzian type power spectrum due to the formation and disappearance of conducting dimers, the current power spectrum densityS m (f) obtained with this gramicidin A derivative showed over several orders of magnitude a clear 1/f behavior. The intensity of this 1/f component was analyzed as a function of the membrane-applied voltage, membrane resistance, electrolyte concentration, and composition. The relationship between the meansquare fluctuation in current and the membrane current mean value was found to follow Hooge's equation, i.e., δI 2=αI m 2 /N f whereN is the number of channels and α is a constant equal to 1.0×10−2. It is suggested that a 1/f type noise was observed because the chemically dimerized form of gramicidin A produces long lasting cation selective channels.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1424
    Keywords: gastric H+K+-ATPase ; caged ATP ; pump currents ; planar lipid films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Membrane fragments containing the H+K−-ATPase from parietal cells have been adsorbed to a planar lipid membrane. The transport activity of the enzyme was determined by measuring electrical currents via the capacitive coupling between the membrane sheets and the planar lipid film. To initiate the pump currents by the ATPase a light-driven concentration jump of ATP from caged ATP was applied as demonstrated previously for Na+K+-ATPase (Fendler, K., Grell, E., Haubs, M., Bamberg, E. 1985.EMBO J. 4:3079–3085). Since H+K+-ATPase is an electroneutrally working enzyme no stationary pump currents were observed in the presence of K+. By separation of the H+ and K+ transport steps of the reaction cycle, however, the electrogenic step of the phosphorylation could be measured. This was achieved in the absence of K+ or at low concentrations of K+. The observed transient current is ATP dependent which can be assigned to the proton movement during the phosphorylation. From this it was conclueded that the K+ transport during dephosphorylation is electrogenic, too, in contrast to the Na+K+-ATPase where the K+ step is electroneutral. The transient current was measured at different ionic conditions and could be blocked by vanadate and by the H+K+-ATPase specific inhibitor omeprazole. An alternative mechanism for activation of this inhibitor is discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 35 (1977), S. 351-375 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The conductance of the gramicidin channel in the presence of alkali ions is strongly reduced when divalent cations such as Ca++ or Ba++ are added to the aqueous solutions in concentrations between 0.1 and 1m. Under the same conditions, carrier-mediated alkali ion transport is not affected by Ca++ and Ba++. Different divalent cations, differ considerably in their blocking action on the gramicidin channel; the effect of Mg++ or Zn++ is much smaller than that of Ca++ and Ba++. Besides reducing the single-channel conductance, the blocking ions also change the current-voltage characteristic of the channel from a nearly, linear to a strongly saturating behavior. These observations suggest that Ca++ or Ba++ (which are not permeable themselves) bind to a site at or near the channel mouth, thereby reducing the rate by which permeable ions enter and leave the channel. The blocking effect is analyzed in terms of the potential energy profile of the permeable ion in the channel. The saturating current-voltage characteristic may be explained by the assumption that in the presence of the blocking ion the passage over the entrance barrier is rate-limiting and, at the same time, only weakly voltage-dependent.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 50 (1979), S. 271-285 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary According to the model of Urry, the cation-permeable gramicidin channel is a dimeric helix formed by association of two peptide monomers linked at their amino ends. In this paper the channel properties of gramicidin analogs are described which have been obtained by chemical modification at the coupling site of the two half-channels. In these analogs the amino terminal-CHO group is replaced by-CO(CH2) n COOH(n=2, 3, 4, 5, 6). All analogs form conducting channels in black lipid membranes with the same general properties as found for gramicidin A. The observation that the channel-forming activity decreases with increasing pH is consistent with the notion that the half-channels are linked at the amino terminus. The channel lifetime of the different analogs varies between 2 msec and ≧50 sec, the longest lifetime being found for the compound withn=3. The single-channel conductance Λ is always smaller than that of gramicidin A, but the reduction of Λ depends on the nature of the permeable ion. Ion specificity was studied at 1m electrolyte by measuring the conductance Λ for different permeable ions (Na+, K+, Cs+). The conductance ratioΛ(Cs+)/Λ(Na+) was found to vary between 2 and 10.5 for the different analogs.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 31 (1977), S. 171-188 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary O-pyromellitylgramicidin is a derivative of gramicidin in which three carboxyl groups are introduced at the terminal hydroxyl end of the peptide. Experiments with artificial lipid membranes indicate that this negatively charged analog forms ion-permeable channels in a way similar to that of gramicidin. If O-pyromellitylgramicidin is added to only one aqueous solution, the membrane conductance remains small, but increases by several orders of magnitude if the same amount is also added to the other side. In accordance with the dimer model of the channel, the membrane conductance under symmetrical conditions is proportional to the square of the aqueous concentration of O-pyromellitylgramicidin over a wide range. The ratioΜ PG/Μ G of the single-channel conductance of O-pyromellitylgramicidin to that of gramicidin is close to unity at high ionic strength, but increases more than fivefold at smaller ionic strength (0.01m). This observation is explained in terms of an electrostatic effect of the fixed negative charges localized near the mouth of the channel. In a mixture of O-pyromellitylgramicidin and gramicidin, unit conductance steps of intermediate size are observed in addition to the conductance steps corresponding to the pure compounds, indicating the formation of hybrid channels. Hybrid channels with preferred orientation may be formed if small amounts of gramicidin and O-pyromellitylgramicidin are added to opposite sides of the membrane. These hybrid channels show a distinct asymmetry in the current-voltage characteristic.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 20 (1975), S. 133-154 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary If a membrane contains ion-conducting channels which form and disappear in a random fashion, an electric current which is passed through the membrane under constant voltage shows statistical fluctuations. Information on the kinetics of channel formation and on the conductance of the single channel may be obtained by analyzing the electrical noise generated in a membrane containing a great number of channels. For this purpose the autocorrelation function of the current noise is measured at different concentrations of the channel-forming substance. As a test system for the application of this technique we have used lipid bilayer membranes doped with gramicidin A. From the correlation time of the current noise generated by the membrane, the rate constants of formation (k R ) and dissociation (k D ) of the channels could be determined. In addition, the mean square of the current fluctuations yielded the single-channel conductance Λ. The values ofk R ,k D , and Λ obtained from the noise analysis agreed closely with the values determined by relaxation measurments and single-channel experiments.
    Type of Medium: Electronic Resource
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