Expression of muscarinic receptor subtypes and M2-muscarinic inhibition of adenylyl cyclase in lung

The relative distribution and absolute quantities of muscarinic receptor subtypes m1, m2, m3, and m4 were determined in membranes of canine trachealis muscle, bronchi, and lung parenchyma by immuno-precipitation with receptor subtype-specific rabbit polyclonal antisera. Additionally, the functional coupling of muscarinic receptors to the inhibition of adenylyl cyclase was related to the presence of m2-muscarinic receptors in each region. Immunoprecipitation identified more total muscarinic receptors in trachealis muscle than in bronchi or lung. m2-Muscarinic receptor predominated in tracheal muscle (372 +/- 85 fmol/mg protein) with fewer m3 receptors (48 +/- 5 fmol/mg protein). Bronchi contained 6.6 +/- 2.0 and 9.2 +/- 1.8 fmol/mg protein of m2 and m3 receptors, respectively. Lung parenchyma contained 13.9 +/- 3.9 fmol/mg protein of m3 receptors. Adenylyl cyclase activity increased in response to guanosine triphosphate and isoproterenol in membranes from all three lung regions, but muscarinic-mediated inh...