CHARACTERIZATION OF BINDING-SITES FOR SIGMA-DENDROTOXIN IN GUINEA-PIG SYNAPTOSOMES - RELATIONSHIP TO ACCEPTORS FOR THE K+-CHANNEL PROBE ALPHA-DENDROTOXIN

Abstract: With use of biologically active 125I‐labelled δ‐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 α‐dendrotoxin, an inhibitor of certain fast‐activating, voltage‐gated K+ channels. Chemical cross‐linking of the δ‐dendrotoxin‐acceptor complex in synaptosomes yielded two specifically labeled polypeptides with molecular masses of 69 and 82 kilodaltons. Although α‐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 δ‐dendrotoxin interacts with a distinct site on the oligomeric acceptors for α‐dendrotoxin. Copyright © 1990, Wiley Blackwell. All rights reserved