The Origin of Subconductance Levels in Voltage-gated K⁺ Channels

Typical single channel recordings in voltage-dependent K⁺ channels show two simple conductance states: open or shut. Considering the fact that K⁺ channels are assembled with four identical subunits, the classical interpretation has been that the conduction pathway is not formed unless all four subunits are in their active positions. In fact, this agrees with the molecular interpretation of the open probability of n⁴ as presented originally by Hodgkin and Huxley (1952), whereby they postulated four n particles that needed to be in the correct position to open the channel. The simple two-conductance level of K⁺ channels was experimentally challenged by Chapman et al. (1997) when they described intermediate conductance levels in drk1 K⁺ channels. In most cases they found that the subconductance levels were extremely short lived, and that could be interpreted as an artifact produced by very fast...