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  • 1
    Electronic Resource
    Electronic Resource
    Heterotypic gap junction channels (connexin26 – connexin32) violate the paradigm of unitary conductance (1995)
    Springer
    Pflügers Archiv 429 (1995), S. 870-872 
    Details
    ISSN: 1432-2013
    Keywords: HeLa cells ; connexin26 ; connexin32 ; gap junction channels ; heterotypic channels ; single channel conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Human HeLa cells transfected with mouse DNA coding for connexin26 (Cx26) or connexin32 (Cx32) were used to examine the properties of heterotypic Cx26 – Cx32 gap junction channels. Intercellular current flow was examined in induced cell pairs by means of the dual voltage-clamp method. We found that Cx26 – Cx32 channels exhibit voltage-dependent conductances, γ j: γj (main state) increases with increasing positivity at the cytoplasmic aspect of the Cx26 connexon and decreases with increasing negativity (slope: 32 pS/100 mV; γ j γj(main state) reaches 48 pS as V j approaches 0 mV); γ j(residual state) with a similar V j-dependence is present when the cytoplasmic end of Cx26 connexon is positive, but absent when it is negative. The single channel data provide an explanation for the asymmetric relationships between the gap junction conductance, g j, and V j. The results are consistent with the notion that docking of two connexons co-determines the biophysical properties of a gap junction channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374812
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  • 2
    Electronic Resource
    Electronic Resource
    Long-chain n-alkanols and arachidonic acid interfere with the V m-sensitive gating mechanism of gap junction channels (1997)
    Springer
    Pflügers Archiv 435 (1997), S. 310-319 
    Details
    ISSN: 1432-2013
    Keywords: Key words Insect gap junctions ; Lipophilic agents ; Chemical uncoupling ; Slow current transitions ; Vm-sensitive gating ; n-Alkanols ; Arachidonic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Experiments were carried out on preformed cell pairs and induced cell pairs of an insect cell line (mosquito Aedes albopictus, clone C6/36). The coupling conductance, g j, was determined with the dual voltage-clamp method. Exposure of preformed cell pairs to lipophilic agents, such as long-chain n-alkanols (n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol) or arachidonic acid, provoked a decrease in g j. Hyperpolarization of both cells led to a recovery of g j. Systematic studies revealed that this phenomenon is caused by a shift of the sigmoidal relationship g j(ss) = f(V m) towards more negative values of V m (where g j(ss) = conductance at steady-state; V m = membrane potential). The shift was dose dependent, it developed with time and was reversible. The longer the hydrocarbon chain of n-alkanols, the lower was the concentration required to produce a given shift. Besides shifting the function g j(ss) = f(V m), arachidonic acid decreased the maximal conductance, g j(max). Single-channel records gained from induced cell pairs revealed that the lipophilic agents interfere with the V m-sensitive slow channel gating mechanism. Application provoked slow current transitions (transition time: 5–40 ms) between an open state of the channel (i.e. main state or residual state) and the closed state; subsequently, fast channel transitions (transition time: 〈 2 ms) involving the main state and the residual state ceased completely. Hyperpolarization of V m or washout of the lipophilic agents gave rise to the inverse sequence of events. The single-channel conductances γ j(main state) and γ j(residual state) were not affected by n-heptanol. We conclude that long-chain n-alkanols and arachidonic acid interact with the V m-sensitive gating mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050517
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature dependence of gap junction properties in neonatal rat heart cells (1993)
    Springer
    Pflügers Archiv 423 (1993), S. 133-139 
    Details
    ISSN: 1432-2013
    Keywords: Neonatal rat heart ; Cardiac cells ; Gap junctions ; Electrical coupling ; Temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cell pairs of neonatal rat hearts were used to study the influence of temperature on the electrical properties of gap junctions. A dual voltage-clamp method was adopted, which allowed the voltage gradient between the cells to be controlled and the intercellular current flow to be measured. Cell pairs with normal coupling revealed a positive correlation between the conductance of the junctional membranes, g j, and temperature. Cooling from 37° C to 14° C led to a steeper decrease in g j, cooling from 14° C to -2° C to a shallower decrease (37° C: g j=48.3 nS; 14° C: g j=21.4 nS;-2°C: g j=17.5 nS), corresponding to a temperature coefficient, Q 10, of 1.43 and 1.14 respectively. The existence of two Q 10 values implies that g j may be controlled by enzymatic reactions. When g j was low, i. e. below 5 nS (conditions: low temperature; treatment with 3 mM heptanol), it showed voltage-dependent gating. This property was not visible when g j was large, i. e. 20–70 nS (conditions: high temperature; normal saline), presumably because of series resistances (pipette resistance). Cell pairs with weak intrinsic coupling and normally coupled cell pairs treated with 3 mM heptanol revealed a positive correlation between the conductance of single gap-junction channels, γ j, and temperature (37° C: 75.6 pS; -2°C: 19.6 pS), corresponding to a Q 10 of 1.41.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374970
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  • 4
    Electronic Resource
    Electronic Resource
    Multiple conductance states of newly formed single gap junction channels between insect cells (1993)
    Springer
    Pflügers Archiv 423 (1993), S. 152-154 
    Details
    ISSN: 1432-2013
    Keywords: Insect cells ; gap junction ; single channel conductance ; channel formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Two cells of an insect cell line (Aedes albopictus, clone C6/36) were pushed together to form a cell pair while the intercellular current flow was monitored. This approach enabled us to study the formation of gap junction channels and explore their electrical properties. We found that the single channels exhibit multiple conductance states. The conductance of a fully open channel was 365 pS; the subconductance steps were 1/7 to 1/5 of the maximal conductance. The voltage gradient across the junction did not influence the conductance of fully open channels, but affected the dwell time at particular conductance states. The latter provides an explanation for the voltage-dependent conductance of gap junction membranes seen in these cells. The very first channel opening always was slow (15–50 ms), suggesting the involvement of a mechanism different from conventional channel gating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374973
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  • 5
    Electronic Resource
    Electronic Resource
    Gap junction channels of insects exhibit a residual conductance (1993)
    Springer
    Pflügers Archiv 424 (1993), S. 192-194 
    Details
    ISSN: 1432-2013
    Keywords: Insect cells ; gap junction ; single channel conductance ; residual conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Formation of gap junction coupled cell pairs was used to assess the basic properties of single gap junction channels. For this purpose, two single cells (clone C6/36, derived from larvae of an insect, Aedes albopictus) were manoeuvred against each other to provoke gap junction channel insertion. Intercellular current flow was measured with a dual voltage-clamp method. Utilizing this approach, we were able to demonstrate that gap junction channels, after formation, do not close completely upon application of a transjunctional voltage gradient, V j. Instead, they exhibit a residual conductance, γ j(residual). On average, γ j(residual) was 64±4 pS (n=40). This corresponds to about 1/6 of the conductance of a fully open channel. The existence of γ j(residual) explains the observation that the conductance of the entire gap junction, g j, decreases only partially at large V j.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374611
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