M2 (Muscarinic) Receptors



M2 receptors are muscarinic receptors that are primarily found in the heart. Binding of M2 receptors by acetylcholine activates a Gi protein subunit and signaling cascade, which causes an intracellular decrease in cyclic AMP levels. Clinically, M2 receptor activation in the heart causes a decrease in heart rate and contractility. This is thought to be the major mechanism by which the vagal nerve causes parasympathetic actions on the heart.

Key Points

  • M2 (Muscarinic) Receptors
    • Associated with Gi protein subunit
      • Inhibits cAMP formation
    • Acts on Heart
      • Main receptor used by vagal nerve (CN X) efferents for inducing parasympathetic effects on the heart
      • Decreases HR (slows heart)
      • Decreases contractility (lowers stroke volume)