Structural bases for blockade and activation of BK channels by Ba ²⁺ ions

Ba ²⁺ increases open probability and blocks the permeation pathway of BK channels. Here we discuss Cryo-EM structures of BK channels with Ba ²⁺ . They reveal that Ba ²⁺ occupies site S3 in the selectivity filter, leading to blockade. Ba ²⁺ are also detected at all high affinity Ca ²⁺ binding sites of the gating ring. However, the architectures of this region in these structures represent intermediate transitions between the extreme close and open configurations.