Positive coupling of cholinergic muscarinic receptors to adenylate cyclase activity in membranes of rat olfactory bulb.

In membranes of rat olfactory bulb acetylcholine stimulated adenylate cyclase activity in a concentration-dependent manner. The maximal stimulation corresponded to 53% increase of basal enzyme activity and was obtained with 100 microM acetylcholine. The concentration of the cholinergic agonist eliciting a half-maximal effect was 0.4 microM. The stimulatory effect of acetylcholine was antagonized by 0.1 microM atropine but not by 10 microM (+)-tubocurarine. Moreover, the addition of micromolar concentrations of GTP was absolutely required for the enzyme stimulation by acetylcholine. The results demonstrate the presence in rat olfactory bulb of muscarinic receptors coupled to stimulation of adenylate cyclase probably via a GTP regulatory protein and provide evidence for a novel signal transduction mechanism of central muscarinic receptors.