Effect of conditioning potential on potassium current kinetics in the frog node

Palti, Yoram; Ganot, Gideon; Stämpfli, R.

doi:10.1016/s0006-3495(76)85686-x

Cited by 42 publications

(45 citation statements)

References 15 publications

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“…No such value of x could be found, which means that 1 K kinetics in this case cannot be presented by n x formalism at all. The same conclusion has also been drawn by Palti et al (1976) for analogous IK--t curves with R. esculenta.…”

Section: Typei Fiberssupporting

confidence: 81%

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

et al. 1980

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The K conductance (gK) kinetics were studied in voltage-clamped frog nodes (Rana ridibunda) in double-pulse experiments. The Cole-Moore translation for gK--t curves associated with different initial potentials (E) was only observed with a small percentage of fibers. The absence of the translation was found to be caused by the involvement of an additional, slow, gK component. This component cannot be attributed to a multiple-state performance of the k channel. It can only be accounted for by a separate, slow K channel, the fast channel being the same as the n4 K channel in R. pipiens. The slow K channel is characterized by weaker sensitivity to TEA, smaller density, weaker potential (E) dependence, and somewhat more negative E range of activation than the fast K channel. According to characteristics of the slow K system, three types of fibers were found. In Type I fibers (most numerous) the slow K channel behaves as and n4 HH channel. In Type II fibers (the second largest group found) the slow K channel obeys the HH kinetics within a certain E range only; beyond this range the exponential decline of the slow gK component is preceded by an E-dependent delay, its kinetics after the delay being the same as those in Type I fibers. In Type III fibers (rare) the slow K channel is lacking, and it is only in these fibers that the Cole-Moore translation of the measured gK--t curves can be observed directly. The physiological role of the fast and slow K channel in amphibian nerves is briefly discussed.

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Section: Typei Fiberssupporting

confidence: 81%

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

et al. 1980

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“…My results confirm the conclusions of Palti et al (1976). Potassium conductance kinetics show a clear dependency on prepulse conditions.…”

Section: Discussionsupporting

confidence: 89%

“…However, in potassium activation I c, is visible from the beginning of the experiments, immediately after the dissection and mounting of the nerve fiber. It can also be seen in the potassium currents, measured by Palti et al (1976) and Begenisich (1979). Capacitive transients, apparently including Ic,, are often subtracted from the membrane currents with an analog circuit that generates the sum of two or three exponentially decaying transients, proportional to the applied voltage step (Atwell et al, 1980;Conti, Neumcke, Nonner & St~impfli, 1980).…”

Section: Discussionmentioning

confidence: 99%

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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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“…These results agree with those of Palti et al (12), who demonstrated that potassium current kinetics are a function of both conditioning pulse amplitude and duration (figures 5 and 6 in ref. 12). Careful examination of the conditioning induced shifts in the crayfish axon (10) reveals that there, too, the shifts are accompanied by a change in the current kinetics.…”

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confidence: 99%

Cole-Moore effect in the frog node.

Ganot¹,

Palti²,

Staempfli³

1978

Proc. Natl. Acad. Sci. U.S.A.

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Potassium currents were recorded from the voltage-clamped frog node (Rana esculenta) during various test pulses that followed hyperpolarizing prepulses of different amplitudes and durations. Both the delay in potassium current onset and the shape of the current trace as a function of time were found to be a function of prepulse parameters. This finding is different from the current trace superposition described by Cole and Moore for a specific test pulse, sodium equilibrium potential in the squid giant axon. The Cole-Moore effect, which was found here only under a specific set of conditions, thus may be a special case rather than the general property of the membrane. The implication of these findings to the various excitable membrane potassium channel models, which are based on the Cole-Moore effect, is discussed.ently: After hyperpolarizing conditioning potentials of different amplitudes and durations there was, in addition to the increase in current turn-on delay, a significant difference in the form of the relationship of potassium current against time, and the curves could not be made to superimpose by shifting them on the time axis.This work attempts to clarify whether the reported differences, between squid and Myxicola on one side and nodal membrane on the other, are due to a basic difference between their properties or to the different conditions under which the experiments were carried out.The turn-on kinetics of axon membrane potassium current and conductance are characterized by an initial delay. In the Hodgkin-Huxley (1) axon model this delay is accounted for by raising the potassium conductance parameter, n, to the 4th power. Within this framework the delay has been interpreted as being due to the need for four potassium channel subunits to be in the so-called open state for the channel, as a whole, to be open. Because these subunits are assumed to have only two states, "open" or "closed," and to be independent of each other, the fraction of channels in which all four subunits are in an open state is given by n4.In 1960 Cole and Moore (2) found that the delay of potassium conductance turn-on was increased by conditioning hyperpolarization. However, the trace of potassium current against time obtained after different conditioning potentials could be made to superimpose by shifting the curves along the time axis. These findings could be accounted for within the Hodgkin-Huxley axon model by raising n to the 25th power. These high powers pose a severe difficulty in giving the Hodgkin-Huxley model the same physical interpretation as above.The above phenomenon, usually referred to as the ColeMoore effect, has been referred to by many workers since it restricts the number of possible models for the potassium gating mechanism in the axon membrane (3-8). However, in spite of the numerous models based on this phenomenon, the experimental data supporting it are limited. Because specific poisons such as tetrodotoxin were unavailable at the time, Cole and Moore (2) used only test pulses that equalled the...

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Effect of conditioning potential on potassium current kinetics in the frog node

Cited by 42 publications

References 15 publications

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

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

Conditioning prepulses and kinetics of potassium conductance in the frog node

Cole-Moore effect in the frog node.

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