G-aS-coupledreceptorsstimulateadenylylcyclase(AC),whichsynthesizescAMPfromATP.IncontrastGai-coupledreceptorsinhibitACandsoreducecAMPformation.ThebgsubunitsfromGaiandotherGproteinsareabletoactivatetheMAPkinasepathwaysandPLCb.GPCRscoupledtotheGaqfamilyofGproteinsstimulatePLCb,whichcleavesmembranephospholipidstoproduceIP3,whichmobilizesintracellularcalcium,andDAG,whichactivatesPKC.Secondmessengerpathwaysthenactivatearangeofeffectorsystemstochangecellbehaviour;inmanycasesthisincludestheregulationofgenetranscription.Dottedlineshowsamoreindirectpathway. Contributor: REFERENCES:StephenJHill,JillianGBaker,andStephenRees.Reporter-genesystemsforthestudyofG-protein-coupledreceptors.CurrentOpinioninPharmacology2001,1,526-32.