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 NH2-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.
Starkus
J G
JG
Research Unit Molecular and Cellular Biophysics, Max Planck Society, D-07747 Jena, Germany.
Kuschel
L
L
Rayner
M D
MD
Heinemann
S H
SH
D000818:Animals; D004330:Drosophila; D029721:Drosophila Proteins; D004553:Electric Conductivity; D005260:Female; D007477:Ions; D009865:Oocytes; D018408:Patch-Clamp Techniques; D010539:Permeability; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000145:classification* / Q000378:metabolism*; D051637:Shaker Superfamily of Potassium Channels; D012964:Sodium / Q000502:physiology; D013997:Time Factors; D014982:Xenopus laevis
D029721:Drosophila Proteins; D007477:Ions; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C496929:Sh protein, Drosophila; D051637:Shaker Superfamily of Potassium Channels; D012964:Sodium; D011188:Potassium