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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