Basenji-greyhound dog: Increased m2 muscarinic receptor expression in trachealis muscle

Airway smooth muscle from asthmatic humans and from the Basenji-greyhound dog (BG) dog is hyporesponsive to β-adrenergic agonist stimulation. Because adenylyl cyclase is under dual regulation in airway smooth muscle, we compared muscarinic receptor-coupled inhibition of adenylyl cyclase in airway smooth muscle from BG and mongrel dogs. Inhibition of forskolin-stimulated adenylyl cyclase activity by the muscarinic M₂ agonist oxotremorine was greater in airway smooth muscle membranes from BG compared with mongrel controls. Quantitative immunoprecipitation studies showed increased numbers of m₂ but not m₃ muscarinic receptors in the BG airway smooth muscle. The enhanced ability of muscarinic agonists to inhibit adenylyl cyclase in BG airway smooth muscle may be due to the greater numbers of muscarinic m₂ receptors, which may account in part for impaired airway smooth muscle relaxation in the BG model of airway hyperresponsiveness.