On the kaliotoxin and dendrotoxin binding sites on rat brain synaptosomes.

The toxic polypeptides alpha-, beta-, gamma- and delta-dendrotoxin (DTX), known to be potent blockers of voltage-dependent potassium channels of the Kv1 family, were purified from the venom of the green mamba Dendroaspis angusticeps. Their binding behaviour to synaptosomal membranes of rat brain was analysed and compared with that of kaliotoxin (KTX), in a competition assay using [(125)I] KTX. alpha-DTX and delta-DTX were found to compete with radioiodinated-KTX (IC(50) of 8 pM and 0.2 nM respectively), whereas gamma-DTX did not. Several minor components that competed with radioiodinated-KTX binding were identified and characterised chemically and biologically.