Monoclonal antibodies can uncouple the main alpha-latrotoxin effects: toxin-induced Ca2+ influx and stimulated neurotransmitter release.

A panel of monoclonal antibodies has been produced against alpha-latrotoxin using black widow spider venom. Five of them were characterized relative to their affinity for alpha-latrotoxin and ability to modify the main toxin effects--to increase calcium permeability of synaptosomes, to stimulate the neurotransmitter release and to form the ion channels in artificial lipid membrane. The results reported here show that: (i) the monoclonal antibodies do not alter the alpha-latrotoxin affinity for the membrane acceptor; (ii) two monoclonal antibodies, A6 and A24, can simultaneously inhibit the alpha-latrotoxin induced Ca2+ uptake and GABA release; (iii) monoclonal antibodies A4 completely block the toxin-induced Ca2+ uptake, but decrease partially the rate of GABA release; (iv) monoclonal antibodies A15 that do not modify the alpha-latrotoxin ability to stimulate Ca2+ uptake and GABA release are able to alter the properties of channels formed by the toxin in the artificial lipid bilayer. From these data we hypothesize that the alpha-latrotoxin molecule has separate functional sites which provide a high-affinity binding to the membrane acceptor, the toxin-induced Ca2+ uptake and toxin-stimulated neurotransmitter release. A separate part of alpha-latrotoxin molecule is responsible for the formation of cationic channels in the artificial lipid bilayer.