Intracellular signaling pathways triggered by GPCRs. Agonist binding to receptors triggers a variety of distinct downstream signaling pathways. Signal propagation can be mediated through G proteins (Gαs, Gαi/o, Gαq/11, Gα12/13, and Gβγ), thereby regulating activities of several kinases (PKA, PKC, and Rho-kinase) and Ca2+ mobilization. Recruitment of β-arrestins resulted from phosphorylation of GPCRs desensitizes G protein coupling, mediates receptor internalization, and initiates β-arrestin-dependent signaling and kinase activation.