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  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of sodium current and gating current in the frog node of Ranvier (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 18-26 
    Details
    ISSN: 1432-2013
    Keywords: Myelinated nerve fibre ; Voltage clamp ; Gating currents ; Chloramine-T
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1. The experiments were done on voltage-clamped nodes of Ranvier of the frog. The aim was to study the kinetics of sodium currentI Na and gating currentI gat over a large potential range (−92 to −12 mV) and to compare the time constants for the turning-on ofI Na orI gat with those for the turning-off measured at the same potential. 2. Sodium tail currents were recorded at different postpulse potentials. Inactivation was inhibited by a few min treatment with 0.5 mM chloramine-T (Wang 1984). The sodium permeability was activated by a 0.4 ms pulse from holding potential (−92 mV) to about 0 mV. At the peak ofI Na the membrane was repolarized to postpulse potentials between −92 and −12 mV. AtE〉 −60 mV the tail currents decayed with two time constants, τ1 and τ2, reflecting presumably the turning-off and the inactivation of the sodium permeability. The relation between τ1 and postpulse potential was bellshaped with a maximum at −32 mV. 3. The tail currents could also be fitted by the Hodgkin-Huxley equation with the sodium activation variablem raised to the second or third power. AtE〈−50 mV τm off was equal to 2 τ1 or 3 τ1, respectively, whereas atE〉−25 mV τm off was equal to τ1. 4. In addition, the time constant of the turning-on of sodium activationm (τm on) was determined, assumingI Na ∼m 2 (with a small initial delay) orI Na ∼m 3 (without an initial delay). At −22 mV and −12 mV the ratio τm off/τm on was close to 1. At −42 mV and −32 mV it was larger than 1 (1.22 and 1.65 for them 2 andm 3 fit, respectively, at −32 mV). 5. A similar pulse program was used to measure the turning-on and turning-off ofI gat in the presence of 300 nM TTX. In the potential range −52 to −22 mV, no significant difference between τoff and τon (measured at the same potential) was found. This is in conflict with the findings of Dubois and Schneider (1982) who reported an inequality τoff 〈 τon. 6. Comparison between τoff of charge movement and τ1 of the tail current yielded τoff/τ1 = 2.8 at −92 mV. This agrees with previous measurements of Neumcke et al. (1976).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00580715
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  • 2
    Electronic Resource
    Electronic Resource
    Gating current experiments on frog nodes of Ranvier treated withCentruroides sculpturatus toxins or aconitine (1987)
    Springer
    Pflügers Archiv 409 (1987), S. 381-393 
    Details
    ISSN: 1432-2013
    Keywords: Myelinated nerve fibre ; Voltage clamp ; Gating currents ; Scorpion toxins ; Aconitine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract (1) Gating currents were recorded from frog nodes of Ranvier treated either with toxins III or IV from the venom of the scorpionCentruroides sculpturatus or with the alkaloid toxin aconitine. (2) Toxins III or IV fromCentruroides sculpturatus (which drastically reduce the sodium permeabilityP Na and slightly shift its voltage dependence in the depolarizing direction) caused a small depolarizing shift of the relation between charge (Q on) and membrane potential (E) without affecting the maximum chargeQ on max. (3) On nodes treated with toxins III or IV fromCentruroides sculpturatus, a depolarizing conditioning pulse (which transiently shifts the descending branch of theI Na(E) curve by up to 60 mV in the hyperpolarizing direction) shifted the midpoint potential (Emid) of theQ on(E) curve by −17 mV and slightly increased the slope of the curve; it also decreasedQ on max markedly but had little effect onQ on measured with small depolarizing pulses. By contrast, massive treatment with aconitine (which irreversibly shifts sodium activation in the hyperpolarizing direction) irreversibly shifted the midpoint potential of theQ on(E) curve from −28.5 to −69 mV and significantly increasedQ on andQ off measured with small depolarizing pulses; concomitantly, the voltage dependence of the on time constant of the charge movement [τon(E)] was shifted by −44 mV. (4) The sodium currentI Na was exponential both in nodes treated with toxins III or IV ofCentruroides sculpturatus and subjected to a depolarizing conditioning pulse and in aconitine-treated nodes; in the latter,I Na started after a delay of 30–40 μs. The time constant of the sodium current, τon Na, was larger than the time constant of the charge movement, τon Q; the ratio τon Q/τon Na was 0.61 and 0.73 in the experiments withCentruroides sculpturatus toxins and aconitine, respectively. (5) The off time constant of the sodium current (τoff Na) was slightly increased in nodes treated withCentruroides sculpturatus toxins and subjected to a depolarizing conditioning pulse, whereas it was markedly increased in aconitine-treated nodes. With the former treatment, the off time constant of the charge movement (τoff Q) was unaffected but with aconitine treatment it was considerably increased although it remained smaller than τoff Na. Consequently, the ratio τoff Q/τoff Na (which is ≥1 in untreated nodes) became smaller than one, reaching values as low as 0.58 and 0.44 in the experiments withCentruroides sculpturatus toxins and aconitine, respectively. The small τoff Q/τoff Na ratio suggests that the channels remain open for an appreciable time after most of the gating charges have returned to their resting position. (6) The results obtained with aconitine resemble the findings on batrachotoxin-treated nodes (Dubois and Schneider 1985), except that in the latter the time constants τon Na and τoff Na of the sodium current are smaller than the corresponding time constants τon Q and τoff Q of the charge movement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583792
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  • 3
    Electronic Resource
    Electronic Resource
    Slow components of the gating current in the frog node of Ranvier (1989)
    Springer
    The protein journal 8 (1989), S. 432-434 
    Details
    ISSN: 1573-4943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01674313
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of reagents modifying carboxyl groups on the gating current of the myelinated nerve fiber (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 63-72 
    Details
    ISSN: 1432-1424
    Keywords: voltage clamp ; node of Ranvier ; gating current ; chemical modification ; carboxyl groups
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of the carboxyl group activating reagent N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on the gating current of the frog node of Ranvier was investigated. A 10-min treatment with 2mm EEDQ (in the presence or absence of 10mm ethylenediamine) irreversibly reduced the slope of the on charge-voltage relationQ on(E), shifted its midpoint potentialE mid in the positive direction and reduced the maximum chargeQ on max measured with strong depolarizing pulses. In six experiments, 2mm EEDQ + 10mm ethylenediamine increased the factork (a reciprocal measure of the slope of theQ on(E) curve) from 16 to 22 mV. In five experiments, 2mm EEDQ alone increasedk from 16 to 23 mV. In a single experiment, 5mm EEDQ + 10mm ethylene diamine increasedk from 17 to 31 mV. The reduction in slope suggests that EEDQ decreases the valence of the gating particles or reduces the fraction of the membrane field that they traverse. In addition, EEDQ (which inhibits inactivation of the sodium current.see M. Rack and K.H. Woll,J. Membrane Biol. 82:41–48, 1984) caused a small increase of the off chargeQ off, and a marked increase of theQ off/Q on ratio, i.e. inhibited charge immobilization. Since the effects of EEDQ occurred regardless of the presence or absence of ethylenediamine, they are probably due to crosslinking reactions. The effects of EEDQ were compared with those of the water-soluble carbodiimide EDC. Treatment with 10 or 50mm EDC (plus 10 or 50mm ethylenediamine) caused a smaller increase ofk than treatment with 2mm EEDQ but reducedQ on max by the same amount.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02209141
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