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 prot ein possessing significant homology to a previously described subunit cloned from bovine muscle. The gene for this subunit is located on chr omosome 5 at band q34 (hslo-beta), There is no evidence for alternativ e RNA splicing of this gene product, hslo-beta mRNA is abundantly expr essed in smooth muscle, but expression levels are low in most other ti ssues, including brain, Brain subregions in which beta-subunit mRNA ex pression is relatively high are the hippocampus and corpus callosum, T he 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 an d/or voltage sensitivity, These data indicate that the beta-subunit sh ows a tissue distribution different to that of the alpha-subunit, and in many tissues there may be no association of alpha-subunits with bet a-subunits, These beta-subunits can play a functional role in the regu lation of neuronal excitability by tuning the Ca2+ and/or the voltage dependence of alpha-subunits.