Anesthesia Pharmacology: Autonomic Pharmacology: Cholinergic Drugs

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Cholinergic Receptors: Subtypes, Tissues, Responses and Molecular Mechanisms

Muscarinic Receptor Coupling Mechanisms

Nicotinic Muscle Receptor
Antagonists Tissue Responses Molecular Aspects



Neuromuscular Junction

Membrane Depolarization leading to muscle contraction

Nicotinic (muscle) receptor's ion channel opening


Nicotinic Neuronal Receptor
Antagonists Tissue Responses Molecular Aspects

Mecamylamine (Inversine)

Autonomic Ganglia

Depolarization: postsynaptic cell activation

  • Nicotinic (muscle) receptor's ion channel opening

Adrenal Medulla

Catecholamine secretion




Muscarinic Type M1
Antagonist Tissue Responses Molecular Aspects


Pirenzepine (more selective)

Autonomic Ganglia

Depolarization (late EPSP)

  • Stimulation of Phospholipase C leading to increased cytosolic Ca2+ .




Muscarinic Type M2
Tissue (Heart) Responses Molecular Aspects

SA node

Decreased phase 4 depolarization; hyperpolarization

  • K+ channel activation through -γ Gi subunits;

  • Gi -mediated inhibition of adenylyl cyclase which decreases intracellular Ca2+ levels.

    • Gi can inhibit directly Ca2+ channel opening.




Decreased contractility; decreased AP duration

AV node

Decreased conduction velocity


Decreased contractility

Adapted from Table 6-2: Lefkowitz, R.J, Hoffman, B.B and Taylor, P. Neurotransmission: The Autonomic and Somatic Motor Nervous Systems, In, Goodman and Gillman's The Pharmacological Basis of Therapeutics, (Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, p119.

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