On the binding of two scorpion toxins to the central nervous system of the cockroach Periplaneta americana

Abstract

Abstract 125I-iododerivatives of the insect toxin (AaH IT1) from Androctonus australis Hector and of one toxin (Ts VII) from Tityus serrulatus were purified by high performance liquid chromatography (HPLC) and used in binding experiments on a nerve cord synaptosomal fraction of cockroach (P. americana). [125I]AaH IT1-b binds specifically and reversibly to a single class of non-interacting binding sites of high affinity ( K d ∗ = 0.14 ± 0.06 nM, n = 5) and low capacity (1.7 ± 0.6 pmol/mg protein). The association (k1) and dissociation (k−1) constants are 3 × 106 M−1 s−1 (n = 2) and 7 × 10−4 s−1 (n = 2), respectively, and are in good agreement with the equilibrium constant. The interaction of [125I]Ts VII-d was irreversible and the association kinetics constant (k) was 2–5 × 107 M−1 s−1 (n = 4). As already shown Ts VII and AaH IT1 compete for the same binding site. The binding site capacity of [125I]Ts VII-d (1.6 ± 0.12 pmol/mg of protein, n = 2) was similar to that obtained with [125I]AaH IT1-b in the present experiments and with [125I]AaH IT1 on an insect synaptosomal fraction of central nervous system, and to that of a similar toxin (toxin γ) on rat brain synaptosomes. The injection of Ts VII in the sixth abdominal ganglion of the cockroach induces a progressive decrease in excitatory postsynaptic potentials and action potential.