Functional coupling of Gi subtype with GABAB receptor/adenylyl cyclase system: analysis using a reconstituted system...

A single molecular species of GTP-binding protein (G protein) has been purified from the bovine cerebral cortex. The immunoblot analysis indicated that the isolated G protein might be Gi1 or Gi2 but not Go, since it was reacted by specific antibodies, anti-Gi alpha 1-2 and anti-Gi alpha 1-1, but not anti-Go alpha. When the Gi protein was reconstituted into phospholipid vesicles with partially purified GABAB receptor and adenylyl cyclase, the stimulation of GABAB receptor by its agonists induced the inhibition of forskolin-stimulated cAMP accumulation. This GABA-induced inhibition was abolished by CGP 55845A, an antagonist of GABAB receptor. These results suggest that a Gi subtype, which was suggested to correspond to Gi1 or Gi2 may be functionally coupled with GABAB receptor/adenylyl cyclase system.