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  • 1
    Electronic Resource
    Electronic Resource
    Voltage-independent Adaptation of Mechanosensitive Channels in Escherichia coli Protoplasts (1998)
    Springer
    The journal of membrane biology 164 (1998), S. 253-262 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Mechanosensation — Ion channel — Adaptation —Escherichia coli— Proteolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Mechanosensitive (MS) ion channels, with 560 pS conductance, opened transiently by rapid application of suction pulses to patches of E. coli protoplast membrane. The adaptation phase of the response was voltage-independent. Application of strong suction pulses, which were sufficient to cause saturation of the MS current, did not abolish the adaptation. Multiple-pulse experimental protocols revealed that once MS channels had fully adapted, they could be reactivated by a second suction pulse of similar amplitude, providing the time between pulses was long enough and suction had been released between pulses. Limited proteolysis (0.2 mg/ml pronase applied to the cytoplasmic side of the membrane patch) reduced the number of open channels without affecting the adaptation. Exposing patches to higher levels of pronase (1 mg/ml) removed responsiveness of the channel to suction and abolished adaptation consistent with disruption of the tension transmission mechanism responsible for activating the MS channel. Based on these data we discuss a mechanism for mechanosensitivity mediated by a cytoplasmic domain of the MS channel molecule or associated protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900410
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  • 2
    Electronic Resource
    Electronic Resource
    Proteolytic activation of a hyperpolarization- and calcium-dependent potassium channel inParamecium (1989)
    Springer
    The journal of membrane biology 112 (1989), S. 91-96 
    Details
    ISSN: 1432-1424
    Keywords: Paramecium ; patch clamp ; K channel ; Ca2+ dependence ; proteolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of proteolysis on a hyperpolarization- and Ca2+-dependent K channel from the surface membrane ofParamecium tetraurelia were examined in the inside-out excised patch mode. Treatment with trypsin, pronase or thermolysin removed the Ca2+-dependence of the channel activation, yielding an increase in channel activity greater than 2.5-fold at all Ca2+ concentrations between 10−4 and 10−8 m. Thermolysin addition-ally removed the voltage dependence of channel opening and gave the most activation among the three proteases tested. Proteolysis did not affect the single-channel conductance. In an analogy to the mechanism of activation of many Ca2+-dependent enzymes it is suggested that thisParamecium channel has a cytoplasmic inhibitory domain which can be removed by proteolysis, and that the physiological activation by Ca2+ is due to a temporary removal of this inhibition. Moreover, these findings indicate structural differences between depolarization-, Ca2+-dependent K channels (BK channels) and the hyperpolarization-, Ca2+-dependent K channels inParamecium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871167
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  • 3
    Electronic Resource
    Electronic Resource
    Activities of a Mechanosensitive Ion Channel in anE. Coli Mutant Lacking the Major Lipoprotein (1993)
    Springer
    The journal of membrane biology 131 (1993), S. 151-160 
    Details
    ISSN: 1432-1424
    Keywords: mechanosensitive channel ; outer membrane ; Escherichia coli/kw] ; lipoprotein ; membrane protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The activity of the mechanosensitive (MS) ion channels in membrane patches, excised fromE. coli spheroplasts, was analyzed using the patch-clamp technique. Outer membranes from a mutant lacking the major lipoprotein (Lpp) and its wildtype parent were examined. The MS-channel activities in the wild-type membrane rarely revealed substates at the time resolution used. These channels showed a stretch sensitivity indicated by the IISP (the suction for ane-fold increase in channel open probability) of 4.9 mm Hg suction. The MS-channel activities oflpp included a prominent substate and showed a weaker mechano-sensitivity with an 1/S p of 10.0 mm Hg. Whereas small amphipaths (chlorpromazine, trinitrophenol) or a larger amphipath (lysolecithin) all activated the MS channel in the wild-type membrane under minimal suction, only the larger lysolecithin could activate the MS channel in thelpp membranes. After lysolecithin addition, thelpp membrane became more effective in transmitting the stretch force to the MS channel, as indicated by a steepening of the Boltzmann curve. We discuss one interpretation of these results, in which the major lipoprotein serves as a natural amphipath inserted in the inner monolayer and the loss of this natural amphipath makes the bilayer less able to transmit the gating force.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02260105
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