receptors

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Receptors and Drug Action Receptors: Specific areas of cell membranes (proteins, glycoproteins)* When bound to ligand, positive or negative biological responce * Few ex. of free receptors in cytoplasma

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Drugs that do not act on receptors: Antacida: CaCO3 + HCl ? Diuretica (osmotic) Akylating agents (cancer) Drugs that do act on receptors: Psoralenes Agonist: Binds to (have affinity for) receptor Binding leads to biolog. responce (Agonists have intrinsic activity / efficacy) Antagonist: Affinity for receptor No intrinsic activity

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Binding of ligand to receptor Covalent bond Ionic bond Hydrogen bond Hydrophobic interaction Covalent bond strong - 50-150 kcal/mol, Normally irreversible bonding ex. Acetylcholine esterase inhibitors

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Reversible inhibitors AcCh Inhibitor Neostigmin Pyridostigmin Myastenia gravis (weak muscles, reduced sensitivity to Acetylcholine) Reversible inhibitor (drugs): k3 (inhib) < k3(AcCh)

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Irreversible Inhibitors Not drugs, nerve gasses, insecticides etc.

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Ionic bond 5-10 kcal/mol, Reversible bonding Hydrogen bond 2-5 kcal/mol, Reversible bonding Hydrophobic interaction 0.5-1 kcal/mol, Reversible bonding

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The occupancy theory: The more receptors sites occupied by ligand, the stronger responce The rate theory: The more ligand-receptor interact / unit time, the stronger responce The induced-fit theory: The macromolecular pertubation theory: (induced fit + rate theory)

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The activation -agregation theory: Always dynamic equilibr.

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Dose-Responce Relationships R locked in membrane (do not move freely) L dissolved in extracellular fluid Reaction on solid - liquid interface

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Types of receptors Super- Endogenous General structures family ligands 1 Fast neurotransmittors Ligand gated ion chanels ex. Acetylcholine 2 Slow neurotransm. ex. noradrenalin G-Protein coupled receptors Hormones 3 Insuline Enzyme coupled receptors Growth factors Catalytic receptors 4 Steroid hormones Cytoplasmic receptors Thyreoid hormones Vitamin A, D

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Ligand gated ion chanels Fastest intracellular responce, ms Binding of ligand - opening of chanel - ion (K+, Na+) in or out of cell - responce Ligands Fast neurotransmittors ex. Acetylcholine (nicotinic reseptors) Nobel prize chemistry 2003, Roderick MacKinnon “for structural and mechanistic studies of ion channels”. http://nobelprize.org/chemistry/laureates/2003/press.html

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G-Protein coupled receptors G-protein: Guanine nucleotide binding protein

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Subtypes of G-proteins - Targets (Second messenger systems) Ion chanels: G12 Na+ / H+ exchange Enzyms: Gi Inhib. Adenylyl cyclase Gs Stimul. Adenylyl cyclase Gq Stimul. Phospholipase C One ligand can bind to more than one type of G-prot. coupled reseptors second messenger pathways

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Subtypes of G-proteins - Targets (Second messenger systems) Ion chanels: G12 Na+ / H+ exchange Enzyms: Gi Inhib. Adenylyl cyclase Gs Stimul. Adenylyl cyclase Gq Stimul. Phospholipase C second messenger pathways

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Enzyme coupled receptors - Catalytic receptors STAT: Signal transducers and activators of transcription Ligands: Peptide hormones

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Cytoplasmic receptors (not bound to cell membranes) (HSP-90: Heat shock protein)

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Receptor subtypes Most receptor classes - several sub-types Each subtypes - differend A(nta)gonists Sub types cholinerge reseptors Nicotinerge receptors Muscarinerge receptors Acetylcholine M1: G-Protein coupled receptors Stimulate phopholipase A M2: G-Protein coupled receptors Inhib. adenylyl cyclase Nmuscle: Ligand gated ion chanels Incr. Na+/Ca2+ Nneuro: Ligand gated ion chanels Incr. Na+/Ca2+

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Spare receptors - Partial agonist

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Desensitizing Sensitizing