A simple model of K+ channel activation in nerve membrane.

A model is proposed for activation of potassium ion channel current, IK, in squid giant axons, which consists of two closed states and one open state. The rate parameter in the forward direction between the two closed states depends upon previous history. That is, it relaxes exponentially to its steady-state value appropriate to the membrane potential of a voltage clamp step rather than change instantaneously as in traditional models of channel gating. The model successfully describes both the enhancement of the delay in activation of IK with relatively negative prepulse potentials, i.e. the Cole-Moore effect, and the time-dependent rising phase of "on" gating current, which has been reported recently for several types of potassium channels.