Cloning, expression, and distribution of a Ca2+-activated K+ channel beta-subunit from human brain

We have cloned and expressed a Ca2+-activated K+ channel beta-subunit from human brain, The open reading frame encodes a 191-amino acid protein possessing significant homology to a previously described subunit cloned from bovine muscle. The gene for this subunit is located on chromosome 5 at band q34 (hslo-beta), There is no evidence for alternative RNA splicing of this gene product, hslo-beta mRNA is abundantly expressed in smooth muscle, but expression levels are low in most other tissues, including brain, Brain subregions in which beta-subunit mRNA expression is relatively high are the hippocampus and corpus callosum, The coexpression of hslo-beta mRNA together with hslo-alpha subunits in either Xenopus oocytes or stably transfected HEK 293 cells gives rise to Ca2+-activated potassium currents with a much increased calcium and/or voltage sensitivity, These data indicate that the beta-subunit shows a tissue distribution different to that of the alpha-subunit, and in many tissues there may be no association of alpha-subunits with beta-subunits, These beta-subunits can play a functional role in the regulation of neuronal excitability by tuning the Ca2+ and/or the voltage dependence of alpha-subunits.