Manifestation of Novel Social Challenges of the European Union in the Teaching Material of Medical Biotechnology Master’s Programmes at the University of Pécs and at the University of Debrecen Identification number: TÁMOP /1/A

EXTRACELLULAR RECEPTORS ION CHANNELS Tímea Berki and Ferenc Boldizsár Signal transduction Manifestation of Novel Social Challenges of the European Union in the Teaching Material of Medical Biotechnology Master’s Programmes at the University of Pécs and at the University of Debrecen Identification number: TÁMOP /1/A

TÁMOP /1/A Scheme of the signal transduction of cell surface receptors LigandReceptor Intracellular signaling Gene expression Biological response

TÁMOP /1/A Receptor families Extracellular receptors: hidrophylic ligands eg. peptide, protein hormones –Ion-channel receptors –7-transmembrane-spanning receptors (7TM) –Catalytic receptors: intrinsic enzyme activity –Non-catalytic receptors: use cytoplasmic tyrosine kinases Intracellular receptors: lipophilic hormones eg. steroids, thyroxin

TÁMOP /1/A ENZYME-LINKED RECEPTORS G-PROTEIN-LINKED RECEPTORS ION-CHANNEL-LINKED RECEPTORS Ions Signal molecule Cytoplasm Plasma membrane GDP    GTP      Enzyme GTP  Signal molecule G-proteinActivated G-proteinActivated enzyme Dimer of signal molecule Inactive catalytic domain Enzyme Active catalytic domain Signal molecule Activated enzyme Extracellular receptor types

TÁMOP /1/A Receptors Ionotropic (ion-channel linked) Metabotropic (use second messengers) GABA A, GABA C, iGlu Glycine, Serotonin, Nicotinic Ach, P2X GABA B, mGlu, Adrenaline, Noradrenaline, Glucagon, FSH, LH, TSH, ADH, parathormone, growth-factors, cytokines Receptors

TÁMOP /1/A Glucagon Secretin Adrenaline ACTH LH FSH Adenylyl cyclase ATPATPcAMPcAMP More receptors using the same second messenger system

TÁMOP /1/A Receptor - ligand interaction Receptor propertiesLigands Ligand binds in the core region of the 7 transmembrane helices 11-cis-retinal (in rhodopsin) Acetylcholine Catecholamines Biogenic amines (histamine, serotomine, etc.) Nucleosides and nucleotides Leukotrienes, prostaglandins, prostacyclins, Thromboxanes Short peptide ligands bind partially in the core region and to the external loops Peptide hormones (ACTH, glucagon, growth hormone) Parathyroid hormone, calcitonin Ligands make several contacts with the N- terminal segment and the external loops Hypothalamic glycoprotein releasing factors (TRH, GnRH) Induce an extensive reorganization of an extended N-terminal segment Metabotropic receptors for neurotransmitters (such as GABA and glutamate) Ca 2+ -sensing receptors, for example on parathyroid cells, thyroidal C-cells (which secrete calcitonin) and on the renal juxtaglomerular apparatus Proteinase activated receptorsReceptors for thrombin amd thrypsin

TÁMOP /1/A Functional groups of ligands Inactive state Active state RrRrRr Inverse agonists Agonists Partial agonists and antagonists

TÁMOP /1/A Ionotropic receptors (ligand-gated ion channels) Ions Ligand Cytoplasm Plasma membrane Ligand gated ion channel

TÁMOP /1/A Ion channel receptors Cys-loop receptors: pentameric structure, 4 transmembrane (TM) regions/subunit –e.g., Acetylcholin (Ach) Nicotinic R – Na + channel –e.g., GABA A, GABA C, Glycine – Cl - channels (inhibitory role in CNS) Glutamate-activated cationic channels: (excitatory role in CNS), tetrameric stucture, 3 TM regions/subunit –e.g., iGlu ATP-gated channels: 3 homologous subunits, 2 TM regions/subunit –e.g., P2X purinoreceptor

TÁMOP /1/A Nicotinic Ach receptorTOP FRONT

TÁMOP /1/A Nicotinic Ach receptor Pore formed from 5 subunits: 2 , , ,  Opening: the 2  units are distorted Desensitization: in the open conformation the , ,  subunits become phosphorylated by Protein kinase A and C

TÁMOP /1/A The axon terminal Axon of motor neuron Terminal button Axon terminal Voltage-gated Na + channel Voltage-gated Acetylcholine Muscle fiber Na + Ca 2+ Voltage-gated Ca 2+ channel Acetylcholinesterase Vesicle of acethylcholine K+K+K+K+ Neurotransmitter-gatedchannelNeurotransmitter-gatedchannel Motor end plate ~4x10 7 nicotinic Ach Rs / end plate

TÁMOP /1/A Electric organs in animals Marine ray Torpedo Freshwater electric eel Electrophorus 2x10 11 nicotinic Ach receptors/end plate!

TÁMOP /1/A Blocking the neuromuscular transmission  -Bungarotoxin: Snake venom (Bungarus multicinctus) Binds to the N-Ach receptor and inactivates Curare (tubocurarin): In South American plants Strychnos toxifera and Chondrodendron tomentosum Indians use as arrow 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

TÁMOP /1/A 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 pesticides e.g. organophosphates Ach AchE