Ion Conduction through C-Type Inactivated Shaker Channels

C-type inactivation of Shaker potassium channels involves entry into a state (or states) in which the inactivated channels appear nonconducting in physiological solutions. However, when Shaker channels, from which fast N-type inactivation has been removed by NH(2)-terminal deletions, are expressed in Xenopus oocytes and evaluated in inside-out patches, complete removal of K(+) ions from the internal solution exposes conduction of Na(+) and Li(+) in C-type inactivated conformational states. The present paper uses this observation to investigate the properties of ion conduction through C-type inactivated channel states, and demonstrates that both activation and deactivation can occur in C-type states, although with slower than normal kinetics. Channels in the C-type states appear “inactivated” (i.e., nonconducting) in physiological solutions due to the summation of two separate effects: first, internal K(+) ions prevent Na(+) ions from permeating through the channel; second, C-type inactivation greatly reduces the permeability of K(+) relative to the permeability of Na(+), thus altering the ion selectivity of the channel.