Mechanism of delayed rectifier K channel gating by extracellar potassium?

[Xalatan]

http://forums.studentdoctor.net/threads/hypokalemia-repolarization-qt-prolongation.313878/

 

Apparently IKr channels are gated by extracellular potassium, and Ke determines the conductance of IKr channels.

 

This supposedly explains why counter-intuitively hypokalaemia prolongs the QT interval and increases the risk of early afterdepolarisation and torsade de pointes.

 

Can someone with insight kindly explain how this gating works at the molecular level? Input would be really appreciated. Is there a pocket on the extra cellular domain of the IKr channel that binds potassium agonistically? I'm thinking along the lines of the GABA-A channel having a modulatory domain for benzodiazepines.