Inhibition of adenylyl cyclase

Some of the neurotransmitter receptors are negatively coupled to adenylyl cyclase. Such receptors relate with G_I proteins which inhibit the activity of the enzyme. Both α- subunit and β/γ-subunits separately block the isoform of adenylyl cyclase general in neurons. The result is that the activity of adenylyl cyclase, and consequently the amount of cAMP in the cell at any given moment, will reflect the balance of the activation of receptors coupled to G_S and those coupled to G_I.