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Extracellular receptors Ion channels

Manifestation of Novel Social Challenges of the European Union in the Teaching Material of Medical Biotechnology Master’s P rogrammes at the University of Pécs and at the University of Debrecen Identification number : TÁMOP-4.1.2-08/1/A-2009-0011.

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Extracellular receptors Ion channels

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  1. Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat theUniversity of Pécs and at the University of Debrecen Identificationnumber: TÁMOP-4.1.2-08/1/A-2009-0011

  2. Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat theUniversity of Pécs and at the University of Debrecen Identification number: TÁMOP-4.1.2-08/1/A-2009-0011 Tímea Berki and Ferenc Boldizsár Signaltransduction ExtracellularreceptorsIon channels

  3. Scheme of the signal transduction of cell surface receptors Ligand Receptor Intracellular signaling Gene expression Biological response

  4. Receptor families • Extracellular receptors:hidrophylicligandseg. peptide, protein hormones • Ion-channel receptors • 7-transmembrane-spanning receptors (7TM) • Catalytic receptors: intrinsic enzyme activity • Non-catalytic receptors: use cytoplasmic tyrosine kinases • Intracellularreceptors:lipophilic hormones eg. steroids, thyroxin

  5. Extracellular receptor types ION-CHANNEL-LINKED RECEPTORS Ions Signal molecule Plasma membrane Cytoplasm G-PROTEIN-LINKED RECEPTORS g g a a Signal molecule b b g a b GTP GDP GTP Enzyme Enzyme Enzyme G-protein Activated G-protein Activated enzyme ENZYME-LINKED RECEPTORS Dimer of signal molecule Signal molecule Enzyme Inactive catalytic domain Active catalytic domain Activated enzyme

  6. Receptors Receptors Ionotropic (ion-channel linked) Metabotropic (use second messengers) • GABAA, GABAC, iGlu • Glycine, • Serotonin, • Nicotinic Ach, • P2X • GABAB, mGlu, Adrenaline, Noradrenaline, Glucagon, FSH, LH, TSH, ADH, parathormone, • growth-factors, cytokines

  7. More receptorsusingthesamesecondmessengersystem ACTH LH FSH Secretin Adrenaline Glucagon Adenylylcyclase ATP cAMP

  8. Receptor - ligandinteraction

  9. Functionalgroups of ligands r r r R R R Partialagonists and antagonists Inverseagonists Agonists Activestate Inactivestate

  10. Ionotropic receptors (ligand-gated ion channels) Ions Ligand Plasmamembrane Cytoplasm Ligandgated ion channel

  11. Ion channel receptors • Cys-loop receptors: pentameric structure, 4 transmembrane (TM) regions/subunit • e.g., Acetylcholin (Ach) Nicotinic R – Na+ channel • e.g., GABAA, GABAC, Glycine – Cl- channels (inhibitory role in CNS) • Glutamate-activated cationic channels: (excitatory role in CNS),tetramericstucture, 3 TM regions/subunit • e.g., iGlu • ATP-gated channels: 3 homologous subunits, 2 TM regions/subunit • e.g., P2X purinoreceptor

  12. Nicotinic Ach receptor FRONT TOP

  13. Nicotinic Ach receptor • Pore formed from 5 subunits: 2a, b, g, d • Opening: the 2a units are distorted • Desensitization: in the open conformation the b, g, d subunits become phosphorylated by Protein kinase A and C

  14. The axonterminal Axon of motor neuron 1 Axonterminal Ca2+ 2 Voltage-gated Ca2+ channel Terminal button Vesicle of acethylcholine 3 Voltage-gated Na+channel 6 5 K+ 4 Neurotransmitter-gated channel Acetylcholine 7 Acetylcholinesterase Na+ Musclefiber Motor end plate ~4x107 nicotinic Ach Rs / end plate

  15. Electricorgansinanimals • Marine ray Torpedo • Freshwater electric eel Electrophorus • 2x1011 nicotinic Ach receptors/end plate!

  16. Blocking the neuromuscular transmission • a-Bungarotoxin: • Snake venom (Bungarusmulticinctus) • Binds to the N-Ach receptor and inactivates • Curare (tubocurarin): • In South American plantsStrychnostoxiferaand Chondrodendrontomentosum • Indiansuseasarrow poison • Curare binds to the same place on the N-Ach receptor than Achetylcholin BUT channel doesn’t open • Causes paralysis of breathing muscles • Used as muscle relaxant in anaesthesia • Antidote: Acetylcholinesterase inhibitors

  17. Acetylcholinesterase(AchE) • Quick removal of Ach from the synaptic space • Ach→ choline+acetyl • Reversible inhibitors:therapeutic use (myasthenia, glaucoma, Alzheimer’s) • Irreversble inhibitors: chemical weapons and pesticidese.g. organophosphates Ach AchE

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