The large conductance Ca2+- and voltage-activated K+ (BK) channel represents a functional subtype of a large group of K+ channels [31–34] that play a dominant role in shaping neuronal activity [18,24,35,36]. It is formed by the association of a core and β auxiliary subunits. The a core subunit possesses many of the common structural features of voltage-gated K+ channels, including an ion-selective pore formed by transmembrane segments S5 and S6 and a voltage-sensing module formed by transmembrane segments S1–S4 (Box 1). In addition, BKCa channels have a long intracellular COOH terminus that forms a Ca2+-sensing module important for activation of the channel [31–33]. The BK channel is ubiquitous throughout the body, expressed in diverse tissues beyond the nervous system. In the brain, virtually all regions express this subunit although at very different levels [14]. Of the four β auxiliary subunits identified so far, only β4 mRNA is expressed in all brain regions examined [37]. Although mRNA coding for β2 or β3 subunits have been reported in both the brain and smooth muscle, to date there is no evidence that they
