What role do G_i proteins play in neurotransmitter signaling?

What role do G_i proteins play in neurotransmitter signaling?

• A. They activate adenylate cyclase, increasing cAMP.
• B. They inhibit adenylate cyclase activity, reducing cAMP levels.
• C. They directly open voltage-gated calcium channels.
• D. They stimulate phospholipase A2.

Answer: (B)

G proteins act as molecular switches that tailor receptor signaling to the right intracellular response. In the inhibitory G protein family, the αi subunit directly shuts down adenylate cyclase when a Gi-coupled receptor is activated, so cAMP levels fall and PKA activity decreases. This dampens a wide range of downstream processes that would normally enhance neurotransmitter signaling or release. The βγ portion released with the αi subunit can also modulate ion channels, such as reducing presynaptic calcium influx, which further lowers neurotransmitter release. So the primary role described here is inhibiting adenylate cyclase and lowering cAMP.

G proteins act as molecular switches that tailor receptor signaling to the right intracellular response. In the inhibitory G protein family, the αi subunit directly shuts down adenylate cyclase when a Gi-coupled receptor is activated, so cAMP levels fall and PKA activity decreases. This dampens a wide range of downstream processes that would normally enhance neurotransmitter signaling or release. The βγ portion released with the αi subunit can also modulate ion channels, such as reducing presynaptic calcium influx, which further lowers neurotransmitter release. So the primary role described here is inhibiting adenylate cyclase and lowering cAMP.