pes of Inactivation in Shaker l6 ’ Channels: Effects of Alterations in the Carboxy-Terminal Region

Shaker potassium channels inactivate and recover from inactivation with multiple exponential components, sug-gesting the presence of multiple inactivation processes. We describe two different types of inactivation in Shaker potassium channels. N-type inactivation can occur as rapidly as a few milliseconds and has been shown to involve an intracellular region at the amino-terminal act-ing as a blocker of the pore. C-type inactivation is inde-pendent of voltage over a range of-25 to +50 mV. It does not require intact N-type inactivation, but is par-tiallycoupled to it. The kinetics of C-type inactivation are quite different for channels with different alternatively spliced carboxy-terminal regions. We have localized the differences in C-type inactivation between the ShB and ShA variants to a single amino acid in the sixth mem-brane-spanning region. N-and C-type inactivation occur by distinct molecular mechanisms