Two types of inactivation in Shaker K+ channels: effects of alterations in the carboxy-terminal region.

Shaker potassium channels inactivate and recover from inactivation with multiple exponential components, suggesting 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 acting as a blocker of the pore. C-type inactivation is independent of voltage over a range of -25 to +50 mV. It does not require intact N-type inactivation, but is partially coupled 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 membrane-spanning region. N- and C-type inactivation occur by distinct molecular mechanisms.