Molecular components of large conductance calcium-activated potassium (BK)channels in mouse pituitary corticotropes

Large-conductance calcium- and voltage- activated potassium (BK) channels p lay a fundamental role in the signaling pathways regulating mouse anterior pituitary corticotrope function. Here we describe the cloning and functiona l characterization of the components of mouse corticotrope BK channels. RT- PCR cloning and splice variant analysis of mouse AtT20 D16:16 corticotropes revealed robust expression of mslo transcripts encoding pore-forming alpha -subunits containing the mouse homolog of the 59-amino acid STREX-1 exon at splice site 2. RT-PCR and functional analysis, using the triterpenoid glyc oside, DHS-1, revealed that native corticotrope BK channels are not functio nally coupled to beta-subunits in vivo. Functional expression of the STREX- 1 containing alpha-subunit in HEK 293 cells resulted in BK channels with ca lcium sensitivity, single-channel conductance, and inhibition by protein ki nase A identical to that of native mouse corticotrope BK channels. This rep ort represents the first corticotrope ion channel to be characterized at th e molecular level and demonstrates that mouse corticotrope BK channels are composed of alpha-subunits expressing the mouse STREX-1 exon.