CHARACTERIZATION OF THE G-PROTEIN INVOLVED IN THE MUSCARINIC STIMULATION OF ADENYLYL-CYCLASE OF RAT OLFACTORY-BULB

We investigated the identity of the G protein mediating the muscarinic stimulation of adenylyl cyclase in rat olfactory bulb membranes by ex amining the sensitivity of this response to selective anti-G protein a ntisera. Preincubation of tissue membranes with the antisera AS/7 (ant i-G(i1/2 alpha)), EC/2 (anti-G(i3 alpha)) G(o alpha), and GO/1 (anti-G (o alpha)) but not with the antiserum QL (anti-G(q/11 alpha)) signific antly attenuated the carbachol-stimulated adenylyl cyclase activity. T hese antisera had no effect on the enzyme activity stimulated by the b eta-adrenergic agonist L-isoproterenol. On the other hand, the anti-G( s alpha) antiserum RM/1 markedly depressed both carbachol- and L-isopr oterenol-stimulated adenylyl cyclase activities. This antiserum also r educed the basal enzyme activity to a similar extent. However, differe nt than the anti-G(i)/G(o) antisera, the RM/1 antiserum failed to affe ct the carbachol-stimulated [S-35]guanosine 5'-O-(3-thiotriphosphate) binding to membrane G proteins, whereas it curtailed the [S-35]guanosi ne 5'-O-(3-thiotriphosphate) binding stimulated by pituitary adenylate cyclase-activating peptide, Exposure to ei ther pertussis toxin or th e anti-G(o alpha) antiserum 9072 but not to cholera toxin or the anti- G(s alpha) antiserum 1191 reduced the high-affinity binding of oxotrem orine M to muscarinic receptors. Moreover, the labeling of a 45-kDa pr otein catalyzed by cholera toxin was markedly stimulated by pituitary adenylate cyclase-activating peptide but not by carbachol. These data indicate that in rat olfactory bulb membranes, muscarinic receptors in teract with both G(i) and G(o) and that these G proteins mediate the s timulation of adenylyl cyclase. Although this response appears to requ ire G(s) activity, no evidence was found for the direct coupling of mu scarinic receptors to G(s).