Functional role of the β subunit of high conductance calcium-activated potassium channels

Abstract

Mammalian high conductance, calcium-activated potassium (maxi-K) channels are composed of two dissimilar subunits, α and β. We have examined the functional contribution of the β subunit to the properties of maxi-K channels expressed heterologously in Xenopus oocytes. Channels from oocytes injected with cRNAs encoding both a and β subunits were much more sensitive to activation by voltage and calcium than channels composed of the α subunit alone, while expression levels, single-channel conductance, and ionic selectivity appeared unaffected. Channels from oocytes expressing both subunits were sensitive to DHS-I, a potent agonist of native maxi-K channels, whereas channels composed of the α subunit alone were insensitive. Thus, α and β subunits together contribute to the functional properties of expressed maxi-K channels. Regulation of coassembly might contribute to the functional diversity noted among members of this family of potassium channels.