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

Shaker K+ channels inactivate through tno 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. (C) 1998 Federation of European Biochemical Societies.