Involvement of beta gamma subunits of G(q/11) in muscarinic M-1 receptor potentiation of corticotropin-releasing hormone-stimulated adenylyl cyclase activity in rat frontal cortex

In the present study, we investigated the involvement of beta gamma subunit s of G(q/11) in the muscarinic M-1 receptor-induced potentiation of cortico tropin-releasing hormone (CRH)-stimulated adenylyl cyclase activity in memb ranes of rat frontal cortex. Tissue exposure to either one of two beta gamm a scavengers, the QEHA fragment of type II adenylyl cyclase and the GDP-bou nd form of the alpha subunit of transducin, inhibited the muscarinic M-1 fa cilitatory effect. Moreover, like acetylcholine (ACh), exogenously added be ta gamma subunits of transducin potentiated the CRH-stimulated adenylyl cyc lase activity, and this effect was not additive with that elicited by ACh. Western blot analysis indicated the expression in frontal cortex of both ty pe II and type IV adenylyl cyclases, two isoforms stimulated by beta gamma subunits in synergism with activated G(S). The M-1 receptor-induced enhance ment of the adenylyl cyclase response to CRH was counteracted by the G(q/11 ) antagonist GpAnt-2A but not by GpAnt-2, a preferential G(i/o) antagonist. In addition, the muscarinic facilitatory effect was inhibited by membrane preincubation with antiserum directed against the C terminus of the alpha s ubunit of G(q/11), whereas the same treatment with antiserum against either G(i1/2) or G(o) was without effect. These data indicate that in membranes of rat frontal cortex, activation of muscarinic M-1 receptors potentiates C RH-stimulated adenylyl cyclase activity through py subunits of G(q/11).