3. Old stuff
          3.1. Old pharm stuff (pre 2009)
              3.1.4. Physiology
                  3.1.4.2. Neurophysiology
                      3.1.4.2.3. Acetylcholine
                          3.1.4.2.3.1. Acetylcholine receptors
 3.1.4.2.3.1.2. Muscarinic acetylcholine receptors 

Muscarinic acetylcholine receptors (mAChR)

[WG21:p101-103]

 

  • Stimulated by muscarine (toxic alkaloid in toadstools)
  • Blocked by atropine
  • 5 different subtypes
    * M1-M4 are all G-protein-coupled receptors
    * M5 is uncertain
  • M1 is abundant in brain
  • M2 is found in heart
    * Decreased cAMP --> Decreased Ca2+ conductance and increased K+ conductance [RD5:p139]
  • M3 is found in smooth muscles
    * Increased IP3 --> Increased intracellular Ca2+ [RD5:p139]
  • M4 is found in smooth muscles and pancreatic acinar and islet tissues
    --> Mediates secretion of pancreatic enzymes and insulin

 

According to [SH4:p266-p267]

  • M1 = CNS and stomach
    --> Inhibition causes decrease in gastric acid secretion
  • M2 = Heart, CNS, airway smooth muscles
    --> Inhibition causes bradycardia
  • M3 = CNS, airway smooth muscles, glandular tissues, vascular endothelial cells
    --> Inhibition causes bronchodilation, vasodilation, and antisialogogue effect
  • M4 = CNS and heart
  • M5 = CNS
  • M1, M3, and M5 activate G proteins
    --> Phospholipase C stimulation and Ca2+ release
  • M2 and M4 activate G proteins
    --> Inhibition of adenylyl cyclase and inhition of voltage-sensitive Ca2+ channels

NB:

  • M1, M3, M5 stimulates phopholipase C via G protein
    * [SH4:p266; RD5:p139]
    * c.f. M1, M4, M5 [WG21:p99]
  • M2, M4 inhibits adenylyl cyclase
    * [SH4:p267; RD5:p139]
    * c.f. M2, M3 [WG21:p99]