Hemicholinum-3 binding sites in the nervous tissue of insects.

High-affinity binding sites for tritiated hemicholinium-3, a potent and selective inhibitor of the sodium-dependent high-affinity choline transport, have been found in synaptosomal membranes from insect ganglia. The binding of hemicholinium to ganglionic membrane preparations was saturable and specific with an apparent K(D) of about 8 nM and a B(max) of 1250 fmol/mg protein. Maximal binding occurred only in the presence of sodium chloride. Upon u.v.-illumination, tritiated hemicholinium-3 appeared to be irreversibly crosslinked to its specific binding sites. Subsequent analysis on SDS-polyacrylamide gels revealed that a single polypeptide band, corresponding to an apparent molecular mass of about 80,000, was labelled.