Agonist-like activity of anti-peptide antibodies directed against an autoimmune epitope on the heart muscarinic acetylcholine receptor.

A synthetic peptide corresponding to amino acids 169-193 of the second extracellular loop of the M2 human muscarinic receptor was used to raise antibodies in rabbits. Affinity purified antibodies specifically recognized a major band with a molecular weight of about 80 kDa on the electrotransferred membrane proteins of both rat ventricles and chinese hamster ovary cells expressing recombinant muscarinic receptors. Incubation of these antibodies with rat myocardial membranes resulted not only in a decrease in the maximal binding capacity, but also in a decrease in receptor antagonist affinity.