The BK_Ca Channel's Ca²⁺-binding Sites, Multiple Sites, Multiple Ions

In this issue, Zeng et al. report results from a series of elegant experiments that, among other contributions, provide new evidence in support of the hypothesis that the BK_Ca channel contains two types of high-affinity Ca²⁺-binding sites. Those that work with this channel will quickly recognize the significance of these data. To the less well initiated, however, it might seem surprising that the number of Ca²⁺-binding sites the BK_Ca channel contains has yet to be firmly established. It has been thirteen years since the BK_Ca channel's pore-forming α subunit was cloned (Atkinson et al., 1991), and its Ca²⁺-sensing mechanism has been studied for over twenty. The truth is, however, that although a good deal of evidence has been produced that supports the notion that the BK_Ca channel has two types of high-affinity Ca...