Lecture 9 Flashcards
What are the adenine nucleotide signalling molecules?
- ATP, ADP
What are the adenine nucleoside signalling molecules?
Adenosine
What are the stages of purine receptor activation?
1) purine synthesis and release 2) extracellular conversions 3) receptor activation
How is adenosine synthesised and released?
1) ATP is hydrolysed= AMP 2) AMP is hydrolysed and converted into adenosine via adenosine kinase - ADK can phosphorylate adenosine to from AMP then later ATP
How do purines leave the presynaptic terminal?
- leakage (tissue damage) - exocytosis - adenosine transporter
How are purines packaged into vesicles?
- VNUT (vesicular nucleotide transporter) - requires Na+ concentration gradient generated by ATP
What is the role of nucleotidases in the extracellular space?
- limit ATP signalling - can give rise to other signalling molecules e.g. ADP and adenosine
What is the role of the adenosine transporter?
- equilibrated transporter - operates on concentration gradients - high extracellular adenosine concentration= removed from extracellular space
What receptors does ATP target?
- P2X (ligand gated ion-channels) - P2Y (GPCRs)
What receptor does ADP target?
P2Y (GPCRs)
What receptor does adenosine target?
P1 (GPCRs)
What are the subtypes of the P2X receptor?
P2x1 to 7
What are the subtypes of the P2Y receptor?
- P2Y1, 12, 13 (ADP) - P2Y2, 11 (ATP)
What are the subtypes of the P1 receptor?
P1A1, A2A, A2B, A3
What are some effects of antagonists at the P1 receptor?
- cognitive disease - neurodegeneration - asthma/cough - diabetes - diarrhoea
What are some effects of agonists at the P1 receptor?
- sleep disorder - stroke - respirator disorders - cystic fibrosis - cancer - cardiac and kidney ischaemia
What does alpha, beta, methylene-ATP do?
- desensitises P2X receptors - increased concentration decreases number of excitatory junction potentials at NEJ
Is the spontaneous release of ATP inhibited by alpha, beta methylene-ATP?
Yes
What is the role of varicosities in purine release?
The release of ATP means it can be converted to adenosine which inactivates receptors stimulated by ATP= fine parasympathetic control
What are areas in the brain where P2X-mediated synaptic transmission has been identified?
- medial habenula - hippocampus The use of nicotinic or glutamate antagonists has little effects in these regions
What is the structure of the P2X receptors?
Trimeric
How does purinergic signalling in pain pathways achieve analgesia?
- P2X antagonists (blocks ATP release from tumour, endothelial and merkel cells) - A1 agonists
What do antagonists at the P2X3 receptor treat?
- chronic cough - tissue damage releases ATP activating P2X3 receptors - AF-219 (Gefapixant)= significant decrease in chronic cough
What is associated with P2X7 activation?
Pain and cell death