Pore accessibility during C-type inactivation in Shaker K+ channels

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Abstract
Shaker K+ channels inactivate through two distinct molecular mechanisms: N‐type, which involves the N‐terminal domain and C‐type that appears to involve structural modifications at the external mouth of the channel. We have tested pore accessibility of the Shaker K+ channel during C‐type inactivation using Ba2+ as a probe. We determined that external Ba2+ binds to C‐type inactivated channels forming an extremely stable complex; i.e. there is Ba2+ trapping by C‐type inactivated channels. The structural changes Shaker channels undergo during C‐type inactivation create high energy barriers that hinder Ba2+ exit to either the extracellular solution or to the intracellular solution.