Alterations in cardiac muscarinic acetylcholine receptors in mice with autoimmune myocarditis and association with circulating muscarinic receptor-related autoantibodies.

Hearts from mice hyperimmunized with cardiac tissue were studied to evaluate the expression and biological activity of muscarinic cholinergic receptors and immunoglobulin G deposits along the immunization period. Mice were sacrificed at 10 day intervals from the first injection up to day 100. Simultaneously, the activity of autoantibodies against muscarinic receptors on normal hearts was also examined in sera. Hearts with autoimmune myocarditis showed a muscarinic receptor-related dysfunction, with an impaired response to exogenous muscarinic agonists and a significant reduction in muscarinic binding sites, both effects being maximum at 40-50 days post-immunization. In addition, serum or immunoglobulin G from mice with myocarditis were able to interact with muscarinic acetylcholine receptors displaying a partial agonist effect. Autoimmune sera and immunoglobulin G reduced heart contractility while inhibited 3H-QNB binding to cardiac acetylcholine receptors in a concentration dependent manner showing the highest effects at days 40-50 and decreased progressively thereafter. The development of muscarinic receptor-related cardiac dysfunction may be associated with the presence of circulating antibodies having muscarinic receptor activity. These studies are of relevance to clinical conditions such as Chagas' disease, where immunological processes involving the cholinergic system are considered to cause cardiomyopathy.