Characteristics of brain Kv1 channels tailored to mimic native counterparts by tandem linkage of alpha subunits: implications for K+ channelopathies

Abstract

Most neuronal Kv1 channels contain Kv1.1, Kv1.2 alpha, and Kvbeta2.1 subunits, yet the influences of their stoichiometries on properties of the (alpha)(4)(beta)(4) variants remain undefined. cDNAs were engineered to contain 0, 1, 2, or 4 copies of Kv1.1 with the requisite number of Kv1.2 and co-expressed in mammalian cells with Kvbeta2.1 to achieve "native-like" hetero-oligomers. The monomeric (Kv1.1 or 1.2), dimeric (Kv1.1-1.2 or 1.2-1.2), and tetrameric (Kv1.1-(1.2)(3)) constructs produced proteins of M(r) approximately 62,000, 120,000, and 240,000, which assembled into (alpha)(4)(beta)(4) complexes. Each alpha cRNA yielded a distinct K(+) current in oocytes, with voltage dependence of activation being shifted negatively as the Kv1.1 content in tetramers was increased. Channels containing 1, 2, or 4 copies of Kv1.1 were blocked by dendrotoxin k (DTX)(k) with similarly high potencies, whereas Kv(1.2)(4) proved nonsusceptible. Accordingly, Kv1.2/beta2.1 expressed in baby hamster kidney cells failed to bind DTX(k); in contrast, oligomers containing only one Kv1.1 subunit in a tetramer exhibited high affinity, with additional copies causing modest increases. Thus, one Kv1.1 subunit largely confers high affinity for DTX(k), whereas channel electrophysiological properties are tailored by the content of Kv1.1 relative to Kv1.2. This notable advance could explain the diversity of symptoms of human episodic ataxia I, which is often accompanied by myokymia, due to mutated Kv1.1 being assembled in different combinations with wild-type and Kv1.2.