Medical Pharmacology Chapter 6:  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

Tubocurarine

α-bungarotoxin

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

CNS

unknown

 

Muscarinic Type M1
Antagonist Tissue Responses Molecular Aspects

Atropine

Pirenzepine (more selective)

Autonomic Ganglia

Depolarization (late EPSP)

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

CNS

Unknown

 

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.

 

 

Atrium

Decreased contractility; decreased AP duration

AV node

Decreased conduction velocity

Ventricle

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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