The general function of the G alpha (s) subunit (Gs) is to activate adenylate cyclase (Tesmer et al. 1997), which in turn produces cAMP, leading to the activation of cAMP-dependent protein kinases (often referred to collectively as Protein Kinase A). The signal from the ligand-stimulated GPCR is amplified because the receptor can activate several Gs heterotrimers before it is inactivated. Another downstream effector of G alpha (s) is the protein tyrosine kinase c-Src (Ma et al. 2000).