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  • 1
    Electronic Resource
    Electronic Resource
    Competitive blockage of the sodium channel by intracellular magnesium ions in central mammalian neurones (1991)
    Springer
    European biophysics journal 19 (1991), S. 109-118 
    Details
    ISSN: 1432-1017
    Keywords: Sodium channel ; Patch clamp ; Cerebellar ; granule cells ; Intracellular magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The aim of this study was to determine from macroscopic current analysis how intracellular magnesium ions, Mg i 2+ , interfere with sodium channels of mammalian neurones. It is reported here that permeation across the sodium channel is voltage- and concentration-dependently reduced by Mg i 2+ . This results in a general reduction of sodium membrane conductance and an outward sodium peak current at large positive potentials. 30 mM Mg i 2+ leads to a negative shift of voltage dependence of sodium channel gating parameters, probably due to the surface potential change of the membrane. This shift alone is, however, insufficient to explain the reduction of outward sodium currents. The blockage by Mg i 2+ is decreased upon increasing intracellular or extracellular Na+ concentration, which suggests that Mg?' interferes with sodium permeation by competitively occupying sodium channels. Using a kinetic model to describe the sodium permeation, the dissociation constant (at zero membrane potential) of Mg i 2+ for the sodium channel has been calculated to be 8.65 ± 1.51 mM, with its binding site located at 0.26 ± 0.05 electrical distance from the inner membrane. This dissociation constant is smaller than that of Na i +, which is 83.76 ± 7.60 mM with its binding site located at 0.75 ± 0.23. The low dissociation constant of Mg i 2+ reflects its high affinity for the sodium channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185451
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  • 2
    Electronic Resource
    Electronic Resource
    Single point mutations of the sodium channel drastically reduce the pore permeability without preventing its gating (1991)
    Springer
    European biophysics journal 20 (1991), S. 127-133 
    Details
    ISSN: 1432-1017
    Keywords: Sodium channel ; Gating current ; Noise analysis ; Site-directed mutagenesis ; Tetrodotoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract 1. Two mutants of the sodium channel II have been expressed inXenopus oocytes and have been investigated using the patch-clamp technique. In mutant E387Q the glutamic acid at position 387 has been replaced by glutamine, and in mutant D384N the aspartic acid at position 384 has been replaced by asparagine.2. Mutant E387Q, previously shown to be resistant to block by tetrodotoxin (Noda et al. 1989), has a single-channel conductance of 4 pS, that can be easily measured only using noise analysis. At variance with the wild-type, the openchannel current-voltage relationship of mutant E387Q is linear over a wide voltage range even under asymmetrical ionic conditions.3. Mutant D384N has a very low permeability for any of the following ions: Cl−, Na+, K+, Li+, Rb+, Ca2+, Mg2+, NH4 + , TMA+, TEA+. However, asymmetric charge movements similar to the gating currents of the Na+-selective wild-type are still observed.4. These results suggest that residues E387 and D384 interact directly with the pathway of the ions permeating the open channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01561134
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  • 3
    Electronic Resource
    Electronic Resource
    Sodium ionic and gating currents in mammalian cells (1990)
    Springer
    European biophysics journal 18 (1990), S. 25-32 
    Details
    ISSN: 1432-1017
    Keywords: Sodium channel ; Gating currents ; Mammalian cells ; Patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Ionic and gating currents from voltage-gated sodium channels were recorded in mouse neuroblastoma cells using the path-clamp technique. Displacement currents were measured from whole-cell recordings. The gating charge displaced during step depolarizations increased with the applied membrane potential and reached saturating levels above 20 mV Prolonged large depolarizations produced partial immobilization of the gating charge, and only about one third of the displaced charge was quickly reversed upon return to negative holding potentials. The activation and inactivation properties of macroscopic sodium currents were characterized by voltage-clamp analysis of large outside-out patches and the single-channel conductance was estimated from nonstationary noise analysis. The general properties of the sodium channels in mouse neuroblastoma cells are very similar to those previously reported for various preparations of invertebrate and vertebrate nerve cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185417
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