lecture: receptors and signaling

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VASUpharm14
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lecture: receptors and signaling
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2010-09-06 20:25:14
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  1. T/F
    The type of receptor present on the target cell determines the effect
    • TRUE
    • receptors have different functions
  2. cell membrane
    consists of:
    • phospholipids,
    • cholesterols,
    • proteins
  3. 2 types of communication for cells
    • 1. intercellular (between)
    • 2. intracellular (within)
  4. Ligands
    • 1st messengers
    • bind to receptors
    • exogenous (drugs)/ endogenous (hormones)
  5. context: ligand activity
    efficacy
    ability of ligand to INITIATE a cellular effect
  6. context: ligand activity
    agonist
    • affinity
    • efficacy
    • endogenous/exogenous
  7. context: ligand activity
    antagonist
    • affinity
    • NO efficacy- blocks agonist
    • endogenous/exogenous
  8. context: receptors
    2 types and function
    • cell membrane
    • intracellular (inside)
    • -modifies signal transduction pathway (on or off)
  9. signal transduction pathway
    • AKA intracellular signaling, second messenger system
    • modification/chain of events of enzymes (kinase/phosphotases) or cell activity (open ion channels, transcription/translation)
  10. context: regulation of receptors by Ligands
    desensitization
    • too much exposure to ligand = inactivate receptor
    • ex: phosphorylation occurs
  11. context: regulation of receptors by Ligands
    down-regulation
    high ligands = low amounts of receptors made
  12. context: regulation of receptors by Ligands
    up-regulation
    low ligands = make more receptors
  13. context: cellular signaling
    5 INTERcellular signaling
    • 1. cell to cell = gap junctions - small molecules
    • 2. autocrine = release to self receptors - autocrine factors
    • 3. paracrine = release to neighbor receptors - paracrine factors
    • 4. nervous = neurons - neurotransmitters
    • 5. endocrine (ex: neuroendocrine) = bloodstream (can go anywhere!) - hormones
    • REMEMBER: (NECAP)
  14. context: cellular signaling
    2 types of receptors of INTRAcellular signaling
    • 1. cell membrane receptors (hydrophilic) - (GPCR, enzyme-linked, ion channel-linked)
    • 2. intracellular receptors (lipophilic) - (steroid, thyroid)
  15. context: GPCR (cell membrane, intracellular)
    other names
    • AKA
    • metabotropic receptors
    • 7-transmembrane spanning receptor
  16. context: GPCR (cell membrane, intracellular)
    coupled with
    • G- proteins
    • Gi, Gs, Gq
  17. context: GPCR (cell membrane, intracellular)
    General scheme
    • ligand and receptor -->transducers (G-protein) --> effectors (AC or PLC) --> second messengers to amplification (cAMP or Calcium/IP3)
    • --> physiological response
  18. context: GPCR (cell membrane, intracellular)
    significance
    • 2% of genome
    • exogenous (senses) > endogenous (neurotransmitters/hormones)
  19. context: GPCR (cell membrane, intracellular)
    G- proteins
    • heterotrimeric = 3 subunits (alpha, beta, gamma)
    • activated when bound to GTP
    • INTRINSIC GTPase activity = self-regulation
  20. context: G- proteins
    Gs va Gi
    • s = stimulate AC
    • i = inhibit AC
    • AC= adenylyl cyclase - membrane bound enzyme
  21. context: GPCR (cell membrane, intracellular)
    Baseline activity???
    • YES.
    • Gi decreases from baseline.
    • cAMP goes down by Gi activating PDE (phosphodiesterase) and deactivate AC
    • both breaks down and stops making cAMP.
  22. context: G-proteins
    Gq
    • activate PLC:
    • --> IP3 --> Ca2+ (constricts smooth muscle around blood vessel)

    2nd pathway: --> Dag --> kinase --> effects.
  23. 2 reasons GCPR are good drug targets
    • 1) location: cell surface
    • 2) ratio: few receptors = amplification after
  24. 4 GPCR disorders
    • 1. mutation -genes = bad receptors, permanent off/on ex: inherited hypocalciuric hypercalcemia
    • 2. processing error - gene ok, misfolding, permanent off/on ex: blindness
    • 3. antibodies - receptor ok = bodies make antibodies that affect receptor (turn off/on) ex: Graves disease
    • 4. toxins - structure and function ok, affect G PROTEIN (receptor off/on) ex: Cholera, Pertussis
  25. context: enzyme-linked receptors/Tyrosine Kinase receptor (main)/Serine.Threonine receptors (less)
    structure 4 parts
    • 1. binding domain
    • 2. transmembrane region
    • 3. kinase domain
    • 4. autophosphorylated region
  26. context: enzyme-linked receptors/Tyrosine Kinase receptor (main)/Serine.Threonine receptors (less)
    receptor activation/signal steps
    • 1. receptors dimerize
    • 2. receptors autophosphorylate (add phosphate groups)
    • 3. activation of intracellular kinases (cascades)/ proteins (RAS- 25% mutated in cancer patients)
    • 4. cell proliferation
  27. context: enzyme-linked receptors/Tyrosine Kinase receptor (main)/Serine.Threonine receptors (less)
    3 Endogenous Ligands
    • 1. insulin (hormone) - intake glucose/a.a, replication/translation
    • 2. growth factors (hormone/paracrine) - cell replication/differentiation
    • 3. cytokines (hormone/paracrine) - cell replication/differentiation + inflammation
  28. context: enzyme-linked receptors/Tyrosine Kinase receptor (main)/Serine.Threonine receptors (less)
    RAS
    • 1 monomeric G-Protein
    • no intrinsic GTPase
    • activates Mitogen-Activated Protein kinase cascade
  29. context: ion channel-linked receptors/ligand-gated/ionotropic
    signaling
    • 1. ligand opens channel
    • 2. ion diffuses
  30. context: ion channel-linked receptors/ligand-gated/ionotropic
    Endogenous Ligands (4)
    • 1. ACh (nicotinic) - Na+ goes in = contraction at neuromuscular junction (skeletal)
    • 2. Serotonin (5HT3) - cations = muscular contractions at intestines and stomach (smooth)
    • 3. Glutamate (NMDA) - cations = increases neuronal activity
    • 4. GABAA - Cl- goes in = decreases neuronal activity
  31. context: intracellular receptors/NHR/ Cytosolic
    signaling steps (3)
    • 1. ligand diffuses through membrane
    • 2. binds in cytosol or nucleus
    • 3. complex migrates to nucleus
  32. context: intracellular receptors/NHR/ Cytosolic
    Endogenous ligands (3)
    • 1. Glucocorticoids (corticosteroids)
    • 2. Estrogen, Progesterone
    • 3. Thyroid hormones

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