A novel β subunit increases rate of inactivation of specific voltage- gated potassium channel α subunits

Voltage-gated potassium channel β subunits are cytoplasmic proteins that co-purify with the pore-forming α subunits. One of these subunits, Kvβ1 from rat brain, was previously demonstrated to increase the rate of inactivation of Kv1.1 and Kv1.4 when co-expressed in Xenopus oocytes. We have cloned and characterized a novel voltage-gated K⁺ channel β subunit. The cDNA, designated Kvβ3, has a 408-amino acid open reading frame. It possesses a unique 79-amino acid N-terminal leader, but is identical with rat Kvβ1 over the 329 C-terminal amino acids. The Kvβ3 transcript was found in many tissues, but was most abundant in aorta and left ventricle of the heart. Co- expression of Kvβ3 with K⁺ channel α subunits shows that this β subunit can increase the rate of inactivation from 4- to 7-fold in a Kv1.4 or Shaker B channel. Kvβ3 had no effect on Kv1.1, unlike Kvβ1 which can increase rate of inactivation of this α subunit more than 100-fold. Other kinetic parameters were unaffected. This study shows that voltage-gated K⁺ channel β subunits are present outside the central nervous system, and that at least one member of this family selectively modulates inactivation of K⁺ channel α subunits.