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Involvement of βγ Subunits of Gq/11 in Muscarinic
 
M1 Receptor Potentiation of Corticotropin‐Releasing Hormone‐Stimulated Adenylyl Cyclase Activity in Rat Frontal Cortex

Abstract : In the present study, we investigated the involvement of βγ subunits of Gq/11 in the muscarinic M1 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 βγ scavengers, the QEHA fragment type II adenylyl cyclase and the GDP‐bound form of the α subunit of transducin, inhibited the muscarinic M1 facilitatory effect. Moreover, like acetylcholine (ACh), exogenously added βγ 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 βγ subunits in synergism with activated Gs. The M1 receptor‐induced enhancement of the adenylyl cyclase response to CRH was counteracted by the Gq/11 antagonist GpAnt‐2A but not by GpAnt‐2, a preferential Gi/o antagonist. In addition, the muscarinic facilitatory effect was inhibited by membrane preincubation with antiserum directed against the C terminus of the α subunit of Gq/11, whereas the same treatment with antiserum against either Gi1/2 or Go was without effect. These data indicate that in membranes of rat frontal cortex, activation of muscarinic M1 receptors potentiates CRH‐stimulated adenylyl cyclase activity through βγ subunits of Gq/11.