Sialic acid is selectively involved in the interaction of agonists with M2 muscarinic acetylcholine receptors

Neuraminidase and slight acid hydrolysis were used to investigate the role of sialic acid residues in the binding of muscarinic agonists and antagonists to membranes from tissues rich in M1 and M2 receptors. Membranes were pretreated with neuraminidase at pH 5 and the binding parameters were determined from competitive experiments with (3H)-quinuclidinylbenzylate. The removal of sialic acid residues reduced the affinity of muscarinic agonists for cerebellum, heart and lung membranes (M2), in contrast to striatum (M1). The affinity of antagonists was not affected. Thus, sialic acid is selectively involved in the interaction of agonists with M2 muscarinic receptors.