FUNCTIONAL-ROLE OF THE BETA-SUBUNIT OF HIGH-CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNELS

Mammalian high conductance, calcium-activated potassium (maxi-K) chann els are composed of two dissimilar subunits, alpha and beta. We have e xamined the functional contribution of the beta subunit to the propert ies of maxi-K channels expressed heterologously in Xenopus oocytes. Ch annels from oocytes injected with cRNAs encoding both alpha and beta s ubunits were much more sensitive to activation by voltage and calcium than channels composed of the a subunit alone, while expression levels , single-channel conductance, and ionic selectivity appeared unaffecte d. Channels from oocytes expressing both subunits were sensitive to DH S-I, a patent agonist of native maxi-K channels, whereas channels comp osed of the a subunit alone were insensitive. Thus, alpha and beta sub units together contribute to the functional properties of expressed ma xi-K channels, Regulation of coassembly might contribute to the functi onal diversity noted among members of this family of potassium channel s.