Barium senses subtle pore changes in a voltage-gated K⁺ channel associated with voltage sensor states and regulatory subunits.

Abstract

In classic models of voltage-dependent channel activation, the pore only opens after the voltage sensor domains (VSDs) activate in an "all-or-none" fashion. Whether the VSD alters open pore properties remains unclear. Here, we examine the properties of the KCNQ1 channel pore in relation with the VSD and regulatory subunits that are located outside of the pore using barium ion (Ba²⁺) block as a probe. We find that the external Ba²⁺ block of KCNQ1 channels is voltage-dependent, and the voltage-dependent channel opening in Ba²⁺ mainly derives from voltage-dependent Ba²⁺ unblock. Open pore conformational changes indicated by the voltage dependence of Ba²⁺ unblock vary with the states of the VSD, the alterations of VSD-pore coupling, and the association with regulatory KCNE subunits. Contrary to the classic view, our results suggest that, instead of being independent of the voltage gating machinery, the pore of KCNQ1 is flexible and influenced by the subtle changes in the voltage sensor state and the environment outside of the pore.