Binding of an alpha scorpion toxin to insect sodium channels is not dependent on membrane potential

The insect-specific Lqh alpha IT toxin resembles alpha scorpion toxins affecting mammals by its amino acid sequence and effects on sodium conductance. The present study reveals that Lqh alpha IT does not bind to rat brain membranes and possesses in locust neuronal membranes a single class of high affinity (Kd = 1.06 +/- 0.15 nM) and low capacity (Bmax = 0.7 +/- 0.19 pmol/mg protein) binding sites. The latter are: (1) distinct from binding sites of other sodium channel neurotoxins; (2) inhibited by sea anemone toxin II; (3) cooperatively interacting with veratridine; (4) not dependent on membrane potential, in contrast to the binding sites of alpha toxins in vertebrate systems. These data suggest the occurrence of (a) conformational-structural differences between insect and mammal sodium channels and (b) the animal group specificity and pharmacological importance of the alpha scorpion toxins.