Biosensor binding assay of BmK AS-1, a novel Na+ channel-blocking scorpion ligand on rat brain synaptosomes

The pharmacological binding of BmK AS-1, a novel Na+ channel-specific ligand purified from Chinese scorpion Buthus martensi Karsch (BmK), has been investigated by biosensor assay. The results showed a fast association rate constant (1.14 x 10(4) M(-1) s(-1)) but a very slow dissociation rate constant (3.24 x 10(-5) s(-1)) for BmK AS-1 binding to the Na+ channel on rat brain synaptosomes. The binding of BmK AS-1 to rat brain synaptosomes could be partially competed by BmK IT2, a depressant insect-selective toxin, but not by BmK I, an alpha-like toxin from the same venom. It was thus further demonstrated that BmK AS-1 might bind to a distinct receptor site, which was partially overlapping that for BmK IT2, but different from that of BmK I on rat brain Na+ channels.