Anti-peptide antibodies against an autoimmune epitope on human muscarinic receptor mimic functional autoantibodies against the same epitope in patients with idiopathic dilated cardiomyopathy.

Abstract

A synthetic peptide corresponding to the sequence 169-193 of the second extracellular loop of the human muscarinic receptor-2 was used to raise antibodies in rabbits. Affinity-purified antibodies were able to interfere with muscarinic receptor radioligand binding and to recognize the muscarinic receptor protein in rats. The antibodies could also exert the physiological effects of muscarinic agonist stimulation as demonstrated by decreases in isoproterenol-stimulated cAMP accumulation in Guinea-pig ventricles, heart beating frequency in cultured meonatal cardiomyocytes, the maximal rate of rise of ventricular pressure and heart rate in rats in-vivo. These results demonstrate that the second extracellular loop of the muscarinic acetylcholine receptor-2 is an immunologically and functionally important domain and that rabbit antibodies have properties comparable to those found for autoantibodies against the same epitope in patients with idiopathic dilated cardiomyopathy.