Biochemical and electrophysiological properties of antibodies against pure acetylcholine receptor from vertebrate muscles and its subunits from Torpedo in relation to experimental myasthenia

Immunization of rabbits with homogeneous preparations of acetylcholine receptor from denervated muscle of cat and chicken, which contained single or multiple sizes of polypeptides respectively, induced myasthenic-like symptoms. One of the resultant antisera, and the IgG fraction thereof, reduced significantly and irreversibly the amplitude of miniature endplate potentials in murine muscle; the effect was not abolished by heat inactivation of complement. This antiserum also retarded the binding of α-bungarotoxin to a solubilised extract of denervated muscle containing homologous receptor. The other five antibody preparations were unable to affect these miniature potentials but many of them did reduce the binding of α-bungarotoxin to denervated muscle receptor in solution and, in some cases, decreased the effectiveness of the latter in blocking neuromuscular transmission. Although inoculation with each of the four individual subunits from the receptor of Torpedo marmorata electroplax did not produce muscle weakness in rabbits, antibodies to α- or β-polypeptides lowered, to a significant extent, the amplitude of spontaneous synaptic potentials in mouse diaphragm muscle. It is concluded that antibodies with direct blocking actions on the receptor-ion channel complex are not common in such immunized animals and their presence cannot be correlated readily with the induction of physical disability. The majority of the antibody species bind to loci distant from the acetylcholine recognition site. Antiserum from one of the immunized rabbits reacted preferentially with receptor from denervated rather than innervated cat and rat muscle, indicating some dissimilarity.