Topic 74 - Membrane receptor signaling

Question 1

Words to include

Answer 1

• Transduction
• G-protein independent
• Transmembraen protein
• Ligand binding part
• Central part
• Inner part
  
  • Phosphorylase activity
• Ligand bond
• IC peptide chain phosphorylase
• Nicotinic acetylcholine receptor
  
  • Ion channel-forming transmembrane protein
  • CNS
  • PNS
  • Conformational change
  • Cation channel
  • Local excitatory potential
  • Action potential
• Glutamate-sensitive receptors
  
  • Post-synaptic membrane-integrated cation channel
  • Glutamate antagonists
    
    • NMDA receptor (N-metil-D-asparate)
      
      • Mg²⁺ dissociation receptor
    • AMPA receptor
    • Kainate-receptor
• Anion receptor
  
  • Anion channels
  • Inhibitory synapses
  • CNS
  • Mediators
    
    • GABA (Gamma Amino Butyric Acid)
      
      • GABA-A receptor
        
        • Ionotropic
      • GABA-B receptor
        
        • Metabotropic
    • Glycine
    • IC cAMP
    • K⁺ channels

Question 2

General

Answer 2

• Transduction = G-protein independent
• Receptor may be a special transmembrane protein of 3 parts:
  
  1. Ligand binding part (on EC side)
  2. Central part (passes through membrane)
  3. Inner part (on IC side – protein continues and exhibits phosphorylase activity)
• Ligand bond on outer surface IC peptide chain phosphorylates/activates receptor or cellular proteins biological action

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Question 3

Name the membrane receptors

Answer 3

1. Nicotinic acetylcholine receptor (n-Ach-R)
2. Glutamate-sensitive receptors
3. Anion receptors

Question 4

Nicotinic actylcholine receptor (N-Ach-R)

Answer 4

• Ion-channel-forming transmembrane protein
• Found in CNS and PNS
• In closed state before binding of ACh
• Binding of ACh → conformational changes → opening of cation channel (open state)
• Influx of cations (e.g. Na⁺) local excitatory potential and stimulation of action potential
• Channel returns to closed state after dissociation of ligand
• Family with 5 membrane-integrated (transmembrane) domains
  
  • Subunits in skeletal muscle:
    
    • 2 α subunits (Ach binding site)
    • 2 β subunits
    • 1 Δ subunit
  • Subunits in nervous tissue: (insensitive to curare)
    
    • 2 α subunits (Ach binding site)
    • 3 β subunits
• The whole receptor serves as an ion channel​
• Ligand binding site (EC side)
• The receptor can be inhibited by d-tubocurarine (curare)

Question 5

Glutamate-sensitive receptors

Answer 5

• Post-synaptic membrane-integrated cation channel
• 3 main groups according to glutamate antagonists:
  
  1. NMDA receptor (N-metil-D-aspartate)
     
     • Binding of Mg²⁺ keeps the receptor closed
     • Mg²⁺ dissociatied after receptor activation
  2. AMPA receptor
  3. Kainate-receptor
• Glutamate also binds to various metabotropic receptors

Question 6

Anion receptors

Answer 6

• Opening of anion channels important in inhibitory synapses of CNS
• 2 main mediators:
  
  1. GABA (Gamma Amino Butyric Acid)
     
     • Acts on GABA-A (ionotropic) or GABA-B (metabotropic)
     • GABA-B decreases IC cAMP and effects K⁺ channels
  2. Glycine