Characterisation of binding sites for delta-dendrotoxin in guinea-pig synaptosomes: relationship to acceptors for the K+-channel probe alpha-dendrotoxin.

With use of biologically active 125I-labelled delta-dendrotoxin, a putative K+-channel ligand, homogeneous, noninteracting, high-affinity acceptors (KD = 0.32 +/- 0.07 nM; Bmax = 0.33 +/- 0.04 pmol/mg) were observed in synaptosomes from guinea-pig cortex. This binding was antagonised noncompetitively by alpha-dendrotoxin, an inhibitor of certain fast-activating, voltage-gated K+ channels. Chemical cross-linking of the delta-dendrotoxin-acceptor complex in synaptosomes yielded two specifically labeled polypeptides with molecular masses of 69 and 82 kilodaltons. Although alpha-dendrotoxin prevents the labelling of both these bands, it cross-linked only a single protein with a molecular mass of 69 kilodaltons. It is concluded that delta-dendrotoxin interacts with a distinct site on the oligomeric acceptors for alpha-dendrotoxin.