Involvement of betagamma subunits of G(q/11) in muscarinic M1 receptor potentiation of corticotropin-releasing hormone-stimulated adenylyl cyclase activity in rat frontal cortex

In the present study, we investigated the involvement of betagamma subunits of G(q/11) in the muscarinic M(1) receptor-induced potentiation of corticotropin-releasing hormone (CRH)-stimulated adenylyl cyclase activity in membranes of rat frontal cortex. Tissue exposure to either one of two betagamma scavengers, the QEHA fragment type II adenylyl cyclase and the GDP-bound form of the alpha subunit of transducin, inhibited the muscarinic M(1) facilitatory effect. Moreover, like acetylcholine (ACh), exogenously added betagamma subunits of transducin potentiated the CRH-stimulated adenylyl cyclase activity, and this effect was not additive with that elicited by ACh. Western blot analysis indicated the expression in frontal cortex of both type II and type IV adenylyl cyclases, two isoforms stimulated by betagamma subunits in synergism with activated G(s). The M(1) receptor-induced enhancement 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 subunit 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 CRH-stimulated adenylyl cyclase activity through betagamma subunits of G(q/11).