Cole-Moore effect in the frog node.

Abstract

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...

Voltage-dependent potassium channels since Hodgkin and Huxley

“…Frankenhaeuser and Hodgkin (66) had found that the sigmoid shape of the K current in squid axon was exaggerated by hyperpolarizing pulses applied just before a depolarizing step: the greater the conditioning hyperpolarization, the greater the apparent delav in the rise of the K current. This phenomenon has been observed in a number of channel ionic currents, including frog node of Ranvier (75,ZOZ), crayfish axons (226), and pheochromocytoma (PC-12) cells (120), as well as in the gating currents from squid axon (23) and Shaker K channels (22). Although n4 schemes do predict such a phenomenon (see Fig.…”

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

“…Somewhat more complicated results have been obtained by Ganot et al (1978) with varying prepulse duration. Our unpublished calculations, analogous to those described above, show that the model proposed could account for most of their results; furthermore, x I = x H = 4 were found to give the best fit.…”

Simultaneous changes in the equilibrium potential and potassium conductance in voltage clamped Ranvier node in the frog.

“…However, this raises serious difficulties for interpreting in physical terms the molecular events underlying the changes in permeability. Alternatively, it can be accounted for according to three interpretations: (i) the K+ conductance is determined by a multi-state process; (ii) the K+ conductance is determined by two or more types of K+ channels; (iii) the K+ current is affected by some extra axonal parameters (Ganot et al 1978). In this paper and the following (Dubois, 1981), several arguments are presented which support these interpretations.…”