Muscarinic cholinergic inhibition of adenylate cyclase in airway smooth muscle.

The goal of our study was to test for an inhibitory effect of acetylcholine on adenylate cyclase activity in canine trachealis muscle. Therefore, cells were dispersed from the muscle enzymatically and lysed, and adenylate cyclase activity was assayed in a membrane suspension isolated from the lysates. Maximal beta-adrenergic stimulation, in the presence of GTP (10(-4) M), increased the activity of adenylate cyclase twofold above the activity induced by GTP alone. In the presence of GTP, acetylcholine (10(-4) M) decreased activity from 97 +/- 21 to 55 +/- 13 pmol cyclic AMP X min-1 X mg protein-1 (means +/- SE; n = 5; P less than 0.05); in the presence of GTP plus isoproterenol (10(-4) M), the acetylcholine-induced decreases were from 163 +/- 29 to 101 +/- 15 pmol cyclic AMP X min-1 X mg protein-1 (P less than 0.05). These decreases were dose dependent and they were altered by a series of cholinergic agents in a pattern consistent with a muscarinic effect. Our results suggest that one biochemical effect of vagal stimulation in the central airways of dogs may be attenuated adenylate cyclase activity in the smooth muscle.