Autonomic & Dopamine Receptors

M1 Receptor: Transmitter & G-protein

ACh — Gq (↑IP3, DAG)

M1 Receptor: Main Action

Increases secretions and GI smooth muscle contraction.

M2 Receptor: Transmitter & G-protein

ACh — Gi (↓cAMP, opens GIRK K⁺ channels)

M2 Receptor: Main Action

Decreases heart rate, force, and AV conduction.

M3 Receptor: Transmitter & G-protein

ACh — Gq (↑IP3, DAG)

M3 Receptor: Main Action

Smooth muscle contraction, gland secretion, endothelial NO release.

M4 Receptor: Transmitter & G-protein

ACh — Gi (↓cAMP)

M5 Receptor: Transmitter & G-protein

ACh — Gq (↑IP3, DAG)

Alpha-1 Receptor: Transmitter & G-protein

NE, EPI — Gq (↑IP3, DAG, ↑Ca²⁺)

Alpha-1 Receptor: Main Action

Vascular smooth muscle contraction, pupil dilation, bladder trigone contraction.

Alpha-2 Receptor: Transmitter & G-protein

NE, EPI — Gi (↓cAMP)

Alpha-2 Receptor: Main Action

Decreases NT release (autoreceptor), inhibits insulin release, lipolysis.

Beta-1 Receptor: Transmitter & G-protein

NE, EPI — Gs (↑cAMP)

Beta-1 Receptor: Main Action

Increases heart rate, contractility, and renin release.

Beta-2 Receptor: Transmitter & G-protein

EPI (mainly) — Gs (↑cAMP)

Beta-2 Receptor: Main Action

Relaxes airway/vascular smooth muscle; increases glycogenolysis and tremor.

Beta-3 Receptor: Transmitter & G-protein

NE — Gs (↑cAMP)

Beta-3 Receptor: Main Action

Stimulates lipolysis in fat cells.

D1 Receptor: Transmitter & G-protein

Dopamine — Gs (↑cAMP)

D1 Receptor: Main Action

Dilates renal and splanchnic vessels.

D2 Receptor: Transmitter & G-protein

Dopamine — Gi (↓cAMP)

D2 Receptor: Main Action

Inhibits adenylyl cyclase at nerve terminals.

nAChR Receptor: Transmitter and G-Protein

ACh --- None

nAChR Receptor: Main Action

Excites (Ganglia, skeletal muscle)