Muscarinic and Adrenergic Receptors (mAChR and AR)

Muscarinic and Adrenergic receptors are two distinct families of G protein-coupled receptors (GPCRs) that serve as the primary mediators of the autonomic nervous system. Muscarinic receptors (M1-M5) are activated by acetylcholine and primarily regulate parasympathetic functions, such as slowing the heart rate, increasing glandular secretions, and contracting smooth muscle in the digestive and urinary tracts (StatPearls: Physiology, Muscarinic Receptor). Adrenergic receptors, including alpha (α1, α2) and beta (β1, β2, β3) subtypes, respond to the catecholamines norepinephrine and epinephrine to mediate sympathetic 'fight or flight' responses, such as bronchodilation and increased cardiac output (StatPearls: Physiology, Adrenergic Receptors). These receptors are among the most important targets in pharmacology, with applications ranging from treating hypertension and heart failure to managing asthma and overactive bladder (PubMed: PMC4917782). Because of their widespread distribution, drugs targeting these receptors often require high subtype selectivity to minimize systemic side effects like dry mouth or heart rhythm disturbances (StatPearls: Physiology, Autonomic Nervous System).

Other names

Muscarinic acetylcholine receptorsAdrenoceptorsCholinergic muscarinic receptorsAdrenergic receptors

Drugs targeting these receptors function as either agonists, which activate the receptor and its associated G-protein signaling cascade, or antagonists, which block the binding of endogenous ligands like acetylcholine or catecholamines. Muscarinic receptors typically signal through Gq (M1, M3, M5) or Gi (M2, M4) proteins, while Adrenergic receptors signal through Gq (alpha-1), Gi (alpha-2), or Gs (beta-1, beta-2, beta-3) proteins to modulate secondary messengers like cAMP or IP3 (StatPearls: Physiology, Muscarinic Receptor; StatPearls: Physiology, Adrenergic Receptors).