alpha subunit compositions of Kv1.1-containing K+ channel subtypes fractionated from rat brain using dendrotoxins

K+ channels from the Kv1 subfamily contain four alpha-subunits and the comb inations (from Kv1.1-1.6) determine susceptibility to dendrotoxin (DTX) hom ologues. The subunit composition of certain subtypes in rat brain was inves tigated using DTXk which only interacts with Kv1.1-containing channels and alpha DTX (and its closely related homologue DTXi) that binds preferentiall y to Kv1.2-possessing homo- or hetero-oligomers. Covalent attachment of [I- 125]DTXk bound to channels in synaptic membranes unveiled subunits of M-r = 78000 and 96000. Immunoprecipitation of these solubilized and dissociated cross-linked proteins with IgG specific for each of the alpha-subunits iden tified Kv1.1, 1.2 and 1.4: this led to assemblies of Kv1.1/1.2 and 1.1/1.4 being established. Kv1.2-enriched channels, purified from rat brain by chro matography on immobilized DTXi, contained Kv1.1, 1.2 and 1.6 confirming one of the above-noted pairs and indicating an additional Kv1.1-containing oli gomer (Kv1.1/1.2/1.6); the notable lack of Kv1.4 excludes a Kv1.1/1.2/1.4 c ombination. On the other hand, channels with Kv1.1 as a constituent, isolat ed using DTXk, possessed Kv1.4 in addition to those found in the DTXi-purif ied oligomers; this provides convergent support for the occurrence of the t hree combinations established above but adds a possible fourth (Kv1.1/1.4/1 .6), though this was not confirmed. Moreover, sequential purification on DT Xi and DTXk resins yielded channels containing only Kv1.1/1.2 but with an a pparent predominance of Kv1.1, reaffirming the latter multimer.