LOCALIZATION OF MUSCARINIC RECEPTORS IN HUMAN HEART BIOPSIES USING RABBIT ANTIPEPTIDE ANTIBODIES

Immunocytochemistry of muscarinic receptors on human heart biopsies fr om patients with heart disease was studied using rabbit antibodies aga inst a synthetic peptide corresponding to amino acids 168-192 of the s econd extracellular loop of the human M2 muscarinic receptor. By using both light and electron microscopic immunocytochemistry techniques, m uscarinic receptors were visualized on sarcolemma of human myocytes fr om patients with different heart diseases such as coronary heart disea se and dilated cardiomyopathy in adults and congenital heart disease i n children. The patchy distribution of immunoreactivity suggests a mus carinergic activity in vivo. These reactivities were abolished by prei ncubation of antibodies with antigenic peptide and were not shown in t he absence of antibodies, Moreover, these antibodies were able to inte rfere with muscarinic ligand binding in myocardium from human dilated cardiomyopathy as shown by decreases in binding sites and antagonist a ffinity. These results demonstrate that the antibodies against the sec ond extracellular loop of the human M2 muscarinic receptor can specifi cally recognize muscarinic receptors in human tissue and display pharm acological activity in human diseased myocardium, confirming their use fulness for the study of localization and function of muscarinergic ac tivity in the human heart. (C) 1995 Academic Press Limited