G-protein coupled platelet receptors

This figure illustrates the function of G-protein coupled platelet receptors. Upon stimulation of the receptor by the appropriate agonist (top left), there is a dissociation of the associated heterotrimeric G-protein into a GTP-binding alpha subunit and a beta-gamma heterodimeric subunit, each of which is then free to stimulate those enzymes that produce second messengers within the platelet. As examples, the G alpha-subclass 12/13 subunit induces platelet shape change, the G alpha-subclass s and the G alpha-subclass i subunits stimulate or inhibit adenyl cyclase activity, respectively, and the G alpha-subclass q subunit activates phospholipase C beta (PLC). The separated G beta-gamma subunit also activates PLC beta as well as phosphatidylinositol 3-kinase (PI3K).