Alternative pre mRNA splicing and gene duplication represent distinct evolutionary mechanisms to generate functional diversity of pore-forming a-subunits of potassium channels. Large conductance calcium- and voltage activated potassium (BK) channels are encoded by a single gene that undergoes extensive alternative pre mRNA splicing resulting in BK channels with dramatically different phenotypes. Splicing can modify calcium sensitivity and channel kinetics, regulate cell surface expression and switch channel regulation by reversible protein phosphorylation and other intracellular signalling cascades. Importantly the splicing decision itself is also dynamically regulated, with distinct patterns of splice variants expressed in different cell types, at different stages in development of the nervous system and in response to a physiological challenge. The functional consequence of alternative splicing on BK channel properties, regulation and function in the nervous system will be explored.