Cytoplasmic BK^sub Ca^ channel intron-containing mRNAs contribute to the intrinsic excitability of hippocampal neurons

High single-channel conductance K... channels, which respond jointly to membrane depolarization and micromolar concentrations of intracellular ... ions, arise from extensive cell-specific alternative splicing of pore-forming α-subunit mRNAs. Here, we report the discovery of an endogenous BK... channel α-subunit intron-containing mRNA in the cytoplasm of hippocampal neurons. This partially processed mRNA, which comprises ...10% of the total BK... channel α-subunit mRNAs, is distributed in a gradient throughout the somatodendritic space. We selectively reduced endogenous cytoplasmic levels of this intron-containing transcript by RNA interference without altering levels of the mature splice forms of the BK... channel mRNAs. In doing so, we could demonstrate that changes in a unique BK... channel α-subunit intron- containing splice variant mRNA can greatly impact the distribution of the BK... channel protein to dendritic spines and intrinsic firing properties of hippocampal neurons. These data suggest a new regulatory mechanism for modulating the membrane properties and ion channel gradients of hippocampal neurons. (ProQuest: ... denotes formulae/symbols omitted.)