G-Protein Signalling Events

How would you expect a non-hydrolyzable GTP analogue to affect signalling events that take place following exposure of a cell expressing α2-adrenergic receptors to:
1) α-agonists
2) β-agonists
3) α-antagonists
4) All of the above in the presence of pertussis toxin or cholera toxin?

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...eptor is termed a Gi subtype because when activated AC activity is inhibited. β receptors are a Gs subtype because they stimulate AC activity. With an analogue of non-hydrolyzable GTP it is important to note that once GTP is bound to the α-subunit it will not be affect by GTPase. A non-hydrolyzable analogue such as GMPPNP will bind to both the α subunit and intracellular GTP.

Drum roll please. . . adding an agonist for α2 will result in a prolonged inhibition (Gi) of adenylate cyclase activity and therefore smooth muscle cell contraction. The reason for this being that the GTP is maintained in an active state with ...