Characterization of the G protein involved in the muscarinic stimulation of adenylyl cyclase of rat olfactory bulb

MC Olianas and P Onali

Department of Neurosciences, University of Cagliari, Italy.

We investigated the identity of the G protein mediating the muscarinic stimulation of adenylyl cyclase in rat olfactory bulb membranes by examining the sensitivity of this response to selective anti-G protein antisera. Preincubation of tissue membranes with the antisera AS/7 (anti-Gi1/2 alpha), EC/2 (anti-Gi3 alpha/Go alpha), and GO/1 (anti-G(o) alpha) but not with the antiserum QL (anti-Gq/11 alpha) significantly attenuated the carbachol-stimulated adenylyl cyclase activity. These antisera had no effect on the enzyme activity stimulated by the beta- adrenergic agonist L-isoproterenol. On the other hand, the anti-Gs alpha antiserum RM/1 markedly depressed both carbachol- and L- isoproterenol-stimulated adenylyl cyclase activities. This antiserum also reduced the basal enzyme activity to a similar extent. However, different than the anti-Gi/Go antisera, the RM/1 antiserum failed to affect the carbachol-stimulated [35S]guanosine 5'-O-(3- thiotriphosphate) binding to membrane G proteins, whereas it curtailed the [35S]guanosine 5'-O-(3-thiotriphosphate) binding stimulated by pituitary adenylate cyclase-activating peptide. Exposure to either pertussis toxin or the anti-Go alpha antiserum 9072 but not to cholera toxin or the anti-Gs alpha antiserum 1191 reduced the high-affinity binding of oxotremorine M to muscarinic receptors. Moreover, the labeling of a 45-kDa protein 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 interact with both Gi and Go and that these G proteins mediate the stimulation of adenylyl cyclase. Although this response appears to require Gs activity, no evidence was found for the direct coupling of muscarinic receptors to Gs.

Volume 49, Issue 1, pp. 22-29, 01/01/1996
Copyright © 1996 by American Society for Pharmacology and Experimental Therapeutics

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