Fig. (1) Schematic diagram showing major GPCR signaling pathways. Upon stimulation, G_s coupled receptors activate adenylyl cyclase (AC) resulting in an increase of cAMP; G_i-coupled receptors inhibit AC, and the βγ subunits activate ERK pathway; G_q coupled receptors activate phospholipase C (PLC) to produce inositol trisphosphate (IP3) and diacylglycerol (DAG), which in turn increases intracellular calcium concentration (Ca²⁺); G₁₂-coupled receptors activate small G protein RhoA GTPase.