The cole-moore effect in nodal membrane of the frogRana ridibunda: Evidence for fast and slow potassium channels

Ilyin, Victor I.; Katina, I. E.; Lonskii, A. V.; Makovsky, V S; Polishchuk, Elena

doi:10.1007/bf01869586

Cited by 30 publications

(19 citation statements)

References 31 publications

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“…The slow tails in 4-AP were fitted at times > 7 ms to reduce the possibility ofcontamination (by the remaining fast tail current and by uncompensated capacitive currents) and because of the presence, following larger depolarizations, of a delay before the decline of the tail current. A similar delay before the decline of the slow tail current was described in some fibres by Ilyin et al (1980). The reversal potential, measured from the instantaneous current-voltage relation following a 200 ms pre-pulse to 0 mV, was unaffected by the addition of 4-AP.…”

Section: Effect Of External Rb+ On Deactivation Kineticssupporting

confidence: 75%

The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.

Plant¹

1986

The Journal of Physiology

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6. External Rb+ slowed the fast inward tail current following all pre-pulses which activate gUt but had no effect on the time course of the slow component of the tail current.7. Regenerative responses, which occur in high [K+] (+300 nM-tetrodotoxin) solutions in current clamp did not repolarize in Rb+. Voltage-clamp experiments showed that inactivation of inward currents is slowed when Rb+ is the charge carrier.8. Replacement of internal K+, by application of Rb+ to the cut ends of the fibre, shifted the reversal potential to more positive potentials but had no effect on the conductance or kinetics.9. External Rb+ has a large number of effects on inward currents, but little effect on outward currents. Internal Rb+ had little effect on outward or inward currents.These results suggest that the properties of the channel depend on the direction and nature of the current.

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Section: Effect Of External Rb+ On Deactivation Kineticssupporting

confidence: 75%

The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.

Plant¹

1986

The Journal of Physiology

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“…Similar conclusions were drawn by Ilyin et al (1980) on Rana ridibunda. Applying a high potassium concentration outside the node,…”

Section: Discussionsupporting

confidence: 87%

“…These calculations were repeated, using parameters obtained by Ilyin et al (1980), who analyzed potassium currents in single nerve fibers from Rana ridibunda according to two populations of potassium channels. Also with their data a similar result for Tsi ~ was obtained.…”

Section: Potassium Deactivation Kinetics (Off-responses)mentioning

confidence: 99%

Conditioning prepulses and kinetics of potassium conductance in the frog node

Bruin

1982

J. Membrain Biol.

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The kinetics of potassium conductance were analyzed in response to voltage-clamp steps with holding potential (-75 mV) as initial condition and after a positive prepulse towards +45 mV of 10-msec duration. As the potassium reversal potential EK altered during potassium current flow, a method to obtain the conductance independent of EK was used. Conductance kinetics at 15 degrees C were analyzed according to the Hodgkin-Huxley (HH) model. The time constant of potassium activation, with holding potential as initial condition, is a monotonous decreasing function of membrane potential. Its value of ca. 9 msec at -50 mV decreases to 1 msec at +30 mV. Changes in EK did not affect the voltage dependency of this time constant. The time constant of potassium deactivation, i.e. the off-response following a 10-msec prepulse towards +45 mV, shows a completely different voltage dependency. At a membrane potential of -90 mV it is approximately 2 msec and gradually increases for more positive voltages towards a maximum value of about 6 msec, that is reached between -5 and 0 mV. At still larger values of membrane voltage this time constant starts to fall again. It is concluded that a HH-model, as applied for a single population of potassium channels, has to be rejected. Computer simulations indicate that an extension to two populations of independent potassium channels, each with HH-kinetics, is also inconsistent with the observed results.

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“…The potassium conductance of myelinated axons, originally described as a uniform system (Frankenhaeuser, 1963), has recently received increasingly complex interpretations involving two (Ilyin, Katina, Lonskii, Makovsky & Polishchuk, 1980) or three (Dubois, 1981 b) kinetically or pharmacologically distinguishable components. This development has to some extent been reflected in the interpretation of potassium current fluctuations.…”

Section: Introductionmentioning

confidence: 99%

“…A number of previous studies have raised the issue ofnon-uniform potassium channels at the node of Ranvier (reviewed by Dubois, 1983). Reasons to suggest this possibility include: the biphasic time course of slow inactivation (Schwarz & Vogel, 1971); the effects of brief conditioning voltage steps on the rise of potassium conductance (Palti, Ganot & Stiimpfli, 1976); biphasic decays of potassium tail currents (Ilyin et al 1980;Dubois, 1981 b); differential blocking effects of TEA, 4-aminopyridine or capsaicine (Ilyin et al 1980;Dubois, 1981bDubois, , 1982; changes of the conductance-voltage relation after long conditioning pulses (Dubois, 1981 b). Two studies specifically propose two or three populations of channels and characterize them to an extent that encourages comparisons with our results.…”

mentioning

confidence: 99%

Non‐stationary fluctuations of the potassium conductance at the node of ranvier of the frog.

Conti¹,

Hille²,

Nonner

1984

The Journal of Physiology

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SUMMARY1. Potassium currents were recorded from voltage-clamped nodes of isolated, myelinated axons of Rana pipiens. Nodes were maintained in a modified Ringer solution containing tetrodotoxin to block sodium current and 47-5 mM-potassium to minimize effects of extracellular potassium accumulation. Voltage protocols included depolarizing pulses lasting a few milliseconds to several seconds. Fluctuations about the ensemble average of the current were characterized in terms of non-stationary variance and autocovariance.2. The fluctuations had a Gaussian amplitude distribution and were virtually free of contaminations from systematic variations of the membrane current. Corrections for background noise were based on measurements done while potassium current was blocked with tetraethylammonium, and on simulations of extrinsic current fluctuations expected to arise from noise in the actual membrane voltage.3. The fluctuations were attributed to variations of nodal potassium conductance, since they were absent at the reversal potential of the potassium current and at membrane voltages that do not activate potassium current. Covariances indicated that voltage steps that reversed a macroscopic potassium current also reversed the sign of the fluctuation. 4. Plots of the conductance variance versus the mean potassium conductance were generated from both the activation and deactivation (tail) phases of the potassium currents at various voltages between -80 and +70 mV. When the current was activated by a small depolarization (-50 mV) the trajectories from both phases were indistinguishable and were fitted by the parabola expected for a single population of channels with only one open-channel conductance. Apparent single-channel conductance from the early activation phase averaged 24 pS and was not significantly voltage dependent.5. In contrast, experiments with large depolarizations (+ 10 to +70 mV) gave significantly different variance-mean trajectories during activation and deactivation and these trajectories were poorly fitted by parabolae. This result indicates that the fluctuations reflect several populations of channels and/or a population of channels that can have several levels of non-zero conductance.

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The cole-moore effect in nodal membrane of the frogRana ridibunda: Evidence for fast and slow potassium channels

Cited by 30 publications

References 31 publications

The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.

The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier.

Conditioning prepulses and kinetics of potassium conductance in the frog node

Non‐stationary fluctuations of the potassium conductance at the node of ranvier of the frog.

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