Many unrelated GPCRs couple with the Gi G-protein subtype. The G-alpha (i) subunit inhibits the production of cAMP from ATP. In turn, this results in decreased activity of cAMP-dependent protein kinase. There are 8 types of G-alpha (i) known to date:G(i)1, G(i)2, G(i)3, G(i)o, G(i)z, G(i)gust (gustducin) and two G(i)t (retinal transducin) (Downes GB and Gautam N, 1999). Once GDP is exchanged for GTP on the alpha subunit, it dissociates from the G-beta-gamma subunit.