Miscel (signal transduction/ receptors/ neurotransmitters)

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Miscel (signal transduction/ receptors/ neurotransmitters)
2013-10-22 16:43:23
Miscel signal transduction receptors neurotransmitters

Miscel (signal transduction/ receptors/ neurotransmitters)
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  1. What are the three types of receptors?
    • 1. Receptors that penetrate the plasma membrane and have intrinsic enzymatic activity. Tyrosine kinases (PDGF, insulin, EGF and FGF receptors), tyrosine phosphatases (CD45), guanylate cyclases (natriuretic peptide receptors) and serine/threonine kinases (e.g. activin and TGF-β receptors). Receptors with intrinsic tyrosine kinase activity are capable of autophosphorylation as well as phosphorylation of other substrates. Additionally, several families of receptors lack intrinsic enzyme activity, yet are coupled to intracellular tyrosine kinases by direct protein-protein interactions
    • 2. Receptors that are coupled, inside the cell, to GTP-binding and hydrolyzing proteins (termed G-proteins). Receptors of the class that interact with G-proteins all have a structure that is characterized by 7 transmembrane spanning domains. These receptors are termed serpentine receptors. Examples of this class are the adrenergic receptors, odorant receptors, and certain hormone receptors (glucagon, angiotensin, vasopressin and bradykinin).
    • 3. Receptors that are found intracellularly and upon ligand binding migrate to the nucleus where the ligand-receptor complex directly affects gene transcription. Because this class of receptors is intracellular and functions in the nucleus as transcription factors they are commonly referred to as the nuclear receptors. Receptors of this class include the large family of steroid and thyroid hormone receptors. Receptors in this class have a ligand-binding domain, a DNA-binding domain and a transcriptional activator domain
  2. What are the features of RTK?
    • Most RTKs are monomers, and their domain structure includes an extracellular ligand-binding domain, a transmembrane domain, and an intracellular domain possessing the tyrosine kinase activity.
    • The insulin and insulin-like growth factor receptors are the most complex in the RTK family being disulfide linked heterotetramers
    • Include: EGF R, NEU/HER2, HER3/ insulin R, IGF-1 R/PDGF R, c-Kit/ FGFR/VEGFR/ HGFR/ neurotrophin receptor family (TRKA, TRKB, TRKC) and NGF receptor
    • Many receptors that have intrinsic tyrosine kinase activity as well as the tyrosine kinases that are associated with cell surface receptors contain tyrosine residues, that upon phosphorylation, interact with other proteins (SH2 homology) of the signaling cascade 
    • The interactions of SH2 domain containing proteins with RTKs or receptor associated tyrosine kinases leads to tyrosine phosphorylation of the SH2 containing proteins.
    • The result of the phosphorylation of SH2 containing proteins that have enzymatic activity is an alteration (either positively or negatively) in that activity.
    • Several SH2 containing proteins that have intrinsic enzymatic activity include phospholipase C(γ (PLCγ, PLC-gamma), the proto-oncogene RAS associated GTPase activating protein (rasGAP), phosphatidylinositol-3-kinase (PI3K), protein phosphatase-1C (PTP1C), as well as members of the SRC family of protein tyrosine kinases (PTKs).
  3. What are some examples of Non-Receptor Protein Tyrosine Kinases (PTKs)?
    • Include JAK and SRC family
    • Most of the proteins of both families of non-receptor PTKs couple to cellular receptors that lack enzymatic activity themselves.
    • This class of receptors includes all of the cytokine receptors (eg the interleukin-2 receptor, IL2R), CD4 and CD8 and TCR
    • Another example of receptor-signaling through protein interaction involves the insulin receptor (IR). This receptor has intrinsic tyrosine kinase activity but does not directly interact, following autophosphorylation, with enzymatically active proteins containing SH2 domains (e.g. PI3K). Instead, the principal IR substrate is a protein termed IRS-1. IRS-1 contains several motifs that resemble SH2 binding consensus sites for the catalytically active subunit of PI3K. These domains allow complexes to form between IRS-1 and PI3K. This model suggests that IRS-1 acts as a docking or adapter protein to couple the IR to SH2 containing signaling proteins
  4. What are the features of Receptor Serine/Threonine Kinases (RSKs)?
    • The receptors for the TGF-β (TGF-beta) superfamily of ligands
    • Ligands first bind to the type II receptors which then leads to interaction with the type I receptors. When the complex between ligand and the 2 receptor subtypes forms, the type II receptor phosphorylates the type I receptor leading to initiation of the signaling cascade and propagates the signal through phosphorylation of the Smad proteins. Once phosphorylated the R-Smads associate with the Co-Smad, Smad4, and the complex migrates to the nucleus where target gene transcription is affected. It is the MH1 domain of the R-Smads that exhibits DNA-binding activity.
    • Include inhibin/activin/BMP/MIS/TGF beta
  5. How does Wnt signaling pathway work?
    • In the absence of Wnt a complex forms consisting of β-catenin, APC, disheveled (Dvl), axin, and GSK3β. Under these conditions, β-catenin is phosphorylated by GSK3β which targets the protein for ubiquitination and degradation.
    • When Wnt binds to its receptor (in this example a frizzled-LRP5/6 complex), the signal transduciton cascade that is initiated results in complexing of Dvl, axin, and GSK3β (inhibited by Dvl) with the receptor complex. This prevents β-catenin phosphorylation, thereby stabilizing the protein which then migrates to the nucleus where it activates transcription factors of the TCF/LEF family
  6. The PKC are a family of.................
    serine/threonine kinases
  7. The mitogen-activated protein (MAP) kinase (MAPK) family constitutes a large family of ...................... that are involved in a wide range of signal transduction cascades
    serine/threonine kinases
  8. The four MAPK cascades are
    • extracellular signal-regulated kinase 1/2 (ERK1/2): proliferation and differentiation
    • c-Jun N-terminal kinase (JNK): response to stress and apoptosis 
    • p38: response to stress and apoptosis
    • ERK5 cascades: responds to both mitogenic signals and cellular stress signals

    components of the JNK and p38 cascades are termed stress-activated protein kinases (SAPKs)
  9. The MAPK signaling cascades are most often initiated by .............................
    receptor-mediated activation of members of the small monomeric G protein family such as Ras, Rac or Rho
  10. ................................. tiers are core components of all MAPK cascades.
    the MAPK, MAPKK and MAP3K
  11. How does the The ERK Cascade work?
    • The extracellular signals are relayed to the ERK cascade via the activation of GPCRs, receptors with intrinsic tyrosine kinase activity (RTKs), and ion channels.
    • The extracellular signal transmission to ERK cascade kinases often involves adaptor proteins such as Shc or Grb2 (growth factor receptor-bound protein 2). These adapter proteins are recruited to the signaling receptor and then in turn activate guanine nucleotide exchange in membrane-bound monomeric G-proteins, such as Ras, rendering these G-proteins active.
    • This in turn allows transmission of the signal to components of the MAP3K tier of the ERK cascade. The primary MAP3K tier proteins are members of the Raf kinase, but can also include TPL2 (also called MAP3K8 and MEKK8) and the stress-activated kinases MEKK1
    • Subsequent to activation of proteins in the MAP3K tier, the signal is transmitted down the cascade to the MAPKK components.
    • Ras directly interacts with and activates Raf. Raf phosphorylates and activates MEK, which in turn phosphorylates and activates ERKs
  12. How does the The p38 Cascade function?
    In addition to receptor-mediated activation of the p38 MAPK cascade, physical stresses such as osmotic shock or heat shock, strongly activate the cascade via receptor-independent processes that includes changes in membrane fluidity. The primary inducing signals are then transmitted to monomeric G-proteins, similarly to the similar process of the ERK cascade, but involves other members of the monomeric G-protein family such as Rac
  13. How does JNK work?
    • Like the p38 MAPK cascade, the JNK cascade plays an important role in the response to cellular stress by inducing apoptosis.
    • Given the similarities in activation triggers between the JNK and p38 cascades, it is apparent that the JNK cascade is responsive to the activation of stress/apoptosis-related receptors, GPCRs, RTKs, and receptor-independent physical stresses.
    • Following activation of the JNK kinases they transmit their signals to adapter that in turn activate the kinases in the MAP4K tier, and on occasion the MAP3K tier, of the JNK cascade.
    • An additional activation scheme of the JNK cascade involves a network of interacting proteins that either induces changes in the activity of adapter proteins, such as members of the TRAF (TNF receptor-associated factor) family, or the activation of monomeric G-proteins such as Rac
  14. What are the function and structure of GPCR?
    • 1) G-proteins are so-called because their activities are regulated by binding and hydrolyzing GTP.
    • 2) When a G-protein is bound to GTP it is in the active ("on") state and when the GTP is hydrolyzed to GDP the protein is in the inactive ("off") state.
    • 3) The G-proteins possess intrinsic GTPase activity that is regulated in conjunction with interaction with membrane-associated signal transducing receptors (termed G-protein coupled receptors, GPCRs) or with intracellular effector protein.
    • 4) There are two major classes of G-protein: those that are composed of three distinct subunits (α, β and γ) and the monomeric class that are related to the archetypal member Ras. This latter class of G-protein is also referred to as the Ras superfamily or the small GTPase family of G-proteins.
    • 5) The structure and function of the monomeric G-proteins is similar to that of the α-subunit of the trimeric G-proteins
    • 6)All known cell surface receptors that are of the G-protein coupled receptor class interact with trimeric G-proteins. The α-subunit of the trimeric class of G-proteins is responsible for the binding of GDP/GTP.
    • 7) When G-proteins are activated by receptors or intracellular effector proteins there is an exchange of GDP for GTP turning on the G-protein which enables it to transmit the original activating signal to downstream effector proteins.
    • 8) In the trimeric class of G-protein, when associated receptor activation stimulates the GDP/GTP exchange in the α-subunit, the protein complex dissociates into separate α and βγ activated complexes. The released and activated βγ complex serves as a docking site for interaction with downstream effectors of the signal transduction cascade.
    • 9)Once the α-subunit hydrolyzes the bound GTP to GDP it re-associates with the βγ complex thereby terminating its activity
    • 10) The GTPase activity of G-proteins is augmented by GTPase activating proteins (GAPs) and the GDP/GTP exchange reaction is catalyzed by guanine nucleotide exchange factors (GEFs).
    • 11) Within the small GTPase family of G-proteins there are guanosine nucleotide dissociation inhibitors (GDIs) that maintain the G-protein in its inactive state.
  15. What are the actions of G proteins?
    • Alpha: 
    • Gs/ Golf: increase AC
    • Gi: decrease AC
    • Gt: ↑ cGMP-PDE
    • Gq: ↑ PLCβs
    • G12: activation of the Rho family of monomeric G-protein
    • betagamma: many similar actions (also opening k channels etc..)
    • Ras: regulation of events of cell proliferation.
    • Rho: regulation of cell morphology through control of cytoskeletal dynamics.
    • Rab : membrane trafficking events.
    • The: control of cell adhesion.
    • Ran : regulation of nuclear transport
    • Rheb : regulation of mTOR 
    • Arf: intracellular vesicle transport
  16. What is the structure of GPCR?
    • Serpentine receptors are so-called because they pass through the plasma membrane seven times.
    • Structural characteristics include the three extracellular loops (EL-1, EL-2, EL-3) and three intracellular loops (IL-1, IL-2, IL-3).
    • Most GPCRs are modified by carbohydrate attachment to the extracellular portion of the protein (typical N-linked carbohydrate attachment)
  17. What are the GPCR?
    • opsins, odorant, taste, monoamines, purines, opioids, chemokines, some small peptide hormones, and the large glycoprotein hormones that consist of thyroid TSH, LH, FSH, PTH, PTHrP, calcitonin, metabotropic glutamate receptors (mGluR), extracellular Ca2+-sensing receptors
    • All are heterotrimeric
    • All act as GEF (when they are activated by ligand binding, they catalyze exchange of GDP tightly bound to the α-subunit of heterotrimeric G-proteins for GTP)
    • All has alpha beta gamma
    • Alpha is effector
    • beta gamma is regulatory
  18. What is the mechanism of receptor desensitization in GPCR?
    • A characteristic feature of GPCR activity following ligand binding is a progressive loss of receptor-mediated signal transduction.
    • This process is referred to as desensitization or adaptation. The events that reflect desensitization of a G-protein coupled signaling system can involve the receptor itself, the G-protein associated with the receptor, and/or the downstream effector(s). In the majority of cases it is impairment of the receptor’s ability to activate its G-protein that accounts for most desensitization, especially within minutes of agonist stimulation.
    • Within milliseconds to minutes of ligand binding, cells can diminish or virtually eliminate the receptor-mediated responses. This process involves phosphorylation of the GPCRs on one or more intracellular domains.
    • On a longer time scale (several hours after ligand binding) the short-term desensitization is augmented by receptor down-regulation which involves the loss of membrane-associated receptor through a combination of protein degradation, transcriptional, and posttranscriptional mechanisms
    • Heterologous desensitization involves phosphorylation of GPCRs by second-messenger-dependent kinases, such as PKA and PKC. Receptor phosphorylation by these kinases, as an isolated event, substantially impairs the ability of GPCRs to stimulate their G-proteins. Homologous desensitization of GPCRs involves a family of kinases termed G-protein coupled receptor  kinases (GRKs) a family of serine/threonine kinases.
    • GRK shares the unusual feature of phosphorylating specifically the agonist-occupied, or activated, conformation of GPCRs.
  19. What are some examples of GPCR diseases?
    • central hypogonadism--> GnRHR
    • central hypothyroidism--> TRHR
    • color blindness--> cone opsins
    • congenital hypothyroidism--> TSHR
    • congenital night blindness--> rhodopsin
    • familial hypocalcemia--> Ca2+ sensing receptor; CASR (gain of function)/AD
    • familial hypocalciuric hypercalcemia--> Ca2+ sensing receptor; CASR (loss of function)/ AD
    • familial non-autoimmune hyperthyroidism--> TSHR (gain)
    • familial male precocious puberty--> LHR gain
    • growth hormone deficiency--> GHRH loss
    • male pseudohermaphroditism--> luteinizing hormone/choriogonadotropin receptor
    • morbid obesity--> MCR4 (loss)
    • neonatal hyperparathyroidism--> Ca2+ sensing receptor, CASR (loss)
    • NDI--> AVPR2 /loss/XL
    • sporadic hyperfunctional thyroid adenomas--> TSHR Gain
  20. What are some intracellular receptors?
    • They are capable of binding hormone as well as directly activating gene transcription
    • steroid and thyroid hormone/ VDR/ Retinoic Acid R
    • RXRs--> bind the retinoid 9-cis-retinoic acid/ form heterodimer with PPARs, LXRs, and FXRs/ if no heterodimer--> bound to hormone response elements (HREs) in DNA and are complexed with co-repressor proteins that include a histone deacetylase
    • PPARs--> alpha endogenous receptor for PUFA and fibrate/ induce hepatic peroxisomal fatty acid oxidation during periods of fasting
    • PPARgamma--> most abundantly in Fat/ bind TZD--> activation of adipocytes leading to increased fat storage and secretion of insulin-sensitizing adipocytokines such as adiponectin
    • PPARδ --> promotion of mitochondrial fatty acid oxidation, energy consumption, and thermogenesis/ ligand for VLDL and PUFA/ activation increase HDL
    • LXR--> mediate cholesterol metabolism
    • FXRs--> receptor for bile acid (decrease bile acid expression)
    • pregnane X receptor (PXR). PXR is highly expressed in the liver and is involved in mediating drug-induced multi-drug clearance/ repress PEPCK (gluconeogenesis)/ regulate bile acid
  21. What is the function of Phosphatidylinositol-3-Kinase (PI3K)?
    • PI3K is tyrosine phosphorylated, and subsequently activated, by various RTKs and receptor-associated PTKs
    • PI3K, associates with and is activated by, the PDGF, EGF, insulin, IGF-1, HGF and NGF receptors. PI3K phosphorylates various phosphatidylinositols at the 3 position of the inositol ring. This activity generates additional substrates for PLCγ allowing a cascade of DAG and IP3 to be generated by a single activated RTK or other protein tyrosine kinases
  22. What are the functions of PLC beta and gamma?
    • Activation of the PLCβ family members occurs via association with GPCRs that are coupled to the Gq class of G-protein.
    • The PLCγ enzymes contain an SH2 domain that allows them to interact with phosphotyrosine residues present on receptors within intrinsic tyrosine kinase activity or with receptor-associated tyrosine kinases. 
    • The members of the PLC family hydrolyze membrane-associated phosphatidylinositol-4,5-bis-phosphate PIP2 resulting in the generation of two second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG)
  23. .....receptors are in nucleus
    Thyroid hormone
  24. In order for cholesterol to be converted to pregnenolone in the adrenal cortex it must be transported into ..........................
    the mitochondria where CYP11A1 resides
  25. What is the rate limiting step in steroidogenesis?
    The transport process (of cholestrol to mitochondria) is mediated by steroidogenic acute regulatory protein (StAR). This transport process is the rate-limiting step in steroidogenesis
  26. What is the enzyme in steroid biosynthesis with two activities?
    CYP17A1 is a single microsomal enzyme that has two steroid biosynthetic activities: 17α-hydroxylase which converts pregnenolone to 17-hydroxypregnenolone (17-OH pregnenolone) and 17,20-lyase which converts 17-OH pregnenolone to DHEA
  27. Zona glomerulosa cells lack the ...............
    P450c17 that converts pregnenolone and progesterone to their C17 hydroxylated analogs
  28. Zona fasciculata and zona reticularis lack ....................
    aldosterone synthase (P450c18) that converts corticosterone to aldosterone
  29. In testis ....cells contain 5 alpha reductase
  30. How does the steroid receptor family function?
    • When these receptors bind ligand they undergo a conformational change that renders them activated to recognize and bind to specific nucleotide sequences.
    • These specific nucleotide sequences in the DNA are referred to as hormone-response elements (HREs).
    • When ligand-receptor complexes interact with DNA they alter the transcriptional level (responses can be either activating or repressing) of the associated gene.
    • Thus, the steroid-thyroid family of receptors all have three distinct domains: a ligand-binding domain, a DNA-binding domain and a transcriptional regulatory domain.
    • Binding of thyroid hormone to its receptor results in release of the receptor from DNA.
    • Binding of glucocorticoid leads to translocation of the ligand-receptor complex from the cytosol to the nucleus
  31. What is the difference between binding of thyroid and steroid hormone to their receptors?
    • Binding of thyroid hormone to its receptor results in release of the receptor from DNA. 
    • Binding of glucocorticoid leads to translocation of the ligand-receptor complex from the cytosol to the nucleus
  32. What are the functions of PPAR receptors?
    • PPAR alpha--> endogenous receptor for PUFA and fibrate/ induce hepatic peroxisomal fatty acid oxidation during periods of fasting
    • PPARgamma--> most abundantly in Fat/ bind TZD--> activation of adipocytes leading to increased fat storage and secretion of insulin-sensitizing adipocytokines such as adiponectin
    • PPARδ --> promotion of mitochondrial fatty acid oxidation, energy consumption, and thermogenesis/ ligand for VLDL and PUFA/ activation increase HDL
  33. ..................... behaves as an endocrine, paracrine, and autocrine
    Insulin-like growth factor-I (IGF-I)
  34. What is the action of ANP?
    The receptors for the natriuretic factors are integral plasma membrane proteins, whose intracellular domains catalyze the formation of cGMP following natriuretic factor-binding. Intracellular cGMP activates a protein kinase G (PKG), which phosphorylates and modulates enzyme activity, leading to the biological effects of the natriuretic factors
  35. The hypothalamic releasing and inhibiting hormones are secreted from the .................
    median eminence of the hypothalamus
  36. What are the nuclei responsible for each hypothalamic hormone?
    • GnRH--> medial preoptic
    • The somatostatin--> periventricular nuclei.
    • TRH and CRH--> medial parts of the periventricular nuclei.
    • GHRH and dopamine--> arcuate nuclei w
  37. What are the hormones that activate PLC?
    Angiotensin II (vascular smooth muscle), Catecholamines (α receptors), GnRH, GHRH, TRH, oxytocin, Vasopressin (V1 receptor, vascular smooth muscle)
  38. What are the hormones that activate or inhibit AC?
    ACTH, LH, FSH, CRH, HCG, TSH, Angiotensin II (epithelial cells), Calcitonin, Catecholamines (β receptors), glucagon, secretin, somatostatin, Vasopressin (V2 receptor, epithelial cells)
  39. What are some characteristics of POMC?
    • POMC is produced in the pituitary, the ARC of the hypothalamus, the nucleus of the solitary tract
    • Within the brain neurons that respond to POMC-derived peptides (termed POMCm neurons) are critical in the regulation of overall energy balance via the melanocortin peptides (primarily α-MSH; this is N-terminally acetylated MSH).
  40. Why are POMC derivative are tissue specific?
    The proteases that recognize these cleavage sites are tissue-specific
  41. How is POMC cleaved?
    • Cleavage sites consist of the sequences, Arg-Lys, Lys-Arg or Lys-Lys.
    • ACTH and β-lipotropin are products generated in the corticotrophic cells of the anterior pituitary under the control of corticotropin releasing hormone (CRH).
    • Alpha-melanocyte stimulating hormone (α-MSH), corticotropin-like intermediate lobe peptide (CLIP), γ-lipotropin and β-endorphin are products generated in the intermediate lobe of the pituitary under the control of dopamine.
  42. How are OT and ADH transferred?
    Both of these hormones are synthesized as prohormones in neural cell bodies of the hypothalamus and mature as they pass down axons in association with carrier proteins termed neurophysins
  43. What are the functions of AVP receptor?
    • V1--> hydrolysis of PIP2 resulting in increased intracellular Ca2+ concentration. The V2 receptors activate --> AC and result in increased cAMP levels.
    • V1 receptors --> blood vessels and vasopressin binding triggers vascular contraction resulting in increased blood pressure.
    • The V2 receptors -->  collecting ducts of the kidneys and are responsible for triggering vasopressin-mediated water retention, thereby, affecting osmolarity
    • Mutations in the gene encoding the V2 receptor--> NDI /XL
  44. While stored in the pituitary, oxytocin is bound to .............
    neurophysin I in Herring bodies
  45. What is the feature of OT receptor?
    The oxytocin receptor is a G-protein coupled receptor (GPCR) whose affinity for ligand is dependent upon Mg2+ and cholesterol, both of which act as positive allosteric regulators
  46. The uterine effect of oxytocin is due, in part, to increased production and release of the .....................from the myometrium and to a lesser extent from the decidua
    prostaglandin PGF2α
  47. What is the mechanism of action of GH and PRL?
    • GH binding to the cell surface receptor induces dimerization of the receptor with subsequent association and activation of JAK2 with the GH receptor in association with the SH2B-β ,  and .
    • JAK2 is then responsible for subsequent activation of the various major groups of signalling molecules. These includes: (1) other receptor (EGFR) and nonreceptor  kinases, (2) members of the MAPK family (3) members of the IRS group which may act as docking proteins for further activation of signaling molecules including phosphatidylinositol-3 kinase; (4) small Ras-like GTPases and (5) STAT family members
  48. Prolactin is known to bind .........and the binding of this metal stabilizes prolactin in the secretory pathway
    zinc (Zn2+)
  49. leptin receptor (also called LEPR-B) is expressed primarily in the .....................
  50. What are the functions of Leptin?
    • Leptin functions by binding to its receptor which is a member of the cytokine receptor family. 
    • Activation of the receptor leads to increased phosphatidylinositol-3-kinase (PI3K) and AMPK activity via activation of the Jak/STAT signaling pathway.
    • One effect of the activation of the Jak/STAT pathway is activation of suppressor of cytokine signaling 3 (SOCS3) which then inhibits leptin signaling in a negative feed-back loop.
    • Leptin binding its receptor also results in the activation of mTOR both in the hypothalamus and in peripheral tissues
    • The role of leptin in the activation of mTOR function is an important factor in the ability of leptin to activate macrophages
  51. Describe the leptin signaling pathway
    • When leptin binds to its receptor (LEPR-B) the receptor undergoes a conformational change that activates the receptor-associated Jak2 tyrosine kinase.
    • Activated Jak2 will autophosphrylate itself as well as phosphorylate the tyrosine (Y) residues in LEPR-B at positions 985, 1077, and 1138.
    • Phosphorylated Y-985 serves as a docking site for SHP2 (SH2 domain containing protein tyrosine phosphatase, also called PTP1D).
    • Phosphorylated Y-1077 serves as a docking site for STAT5 (signal transduction and activation of transcription 5).
    • Phosphorylated Y-1138 serves as a docking site for STAT3.
    • When SHP2, STAT5, and STAT3 bind to phosphorylated LEPR-B they themselves are activated by Jak2-mediated phosphorylation.
    • Activated SHP2 in turn activates the ERK1/2 (extracellular-regulated kinase 1/2) signal pathway that results in increased transcription of the EGR-1 gene.
    • Activated STAT3 in turn activates the transcription of SOCS3 (suppressor of cytokine signaling 3). SOCS3 will then interact with Y-985 and attenuate signaling from SHP2 as well as interact with Jak2 and attenuate its tyrosine kinase activity resulting in a negative feed-back loop
  52. What is the function of adiponectin?
    • The AdipoRs stimulate the phosphorylation and activation of AMPK. The adiponectin-mediated activation of AMPK results in increased glucose uptake, increased fatty acid oxidation, increased phosphorylation and inhibition of acetylCoA carboxylase (ACC) in muscle.
    • In the liver the result is reduced activity of gluconeogenic enzymes and glucose output.
    • Adiponectin also plays an important role in hemostasis by suppressing TNFα-mediated inflammatory changes in endothelial cell responses and inhibiting vascular smooth muscle cell proliferation.
    • Activation of AMPK activity in endothelial cells results in increased fatty acid oxidation and activation of endothelial NO synthase (eNOS).
  53. overexpression of resistin in human heptocytes impairs ..................
    insulin-stimulated glucose uptake and glycogen synthesis
  54. What is the function of Irisin?
    Irisin expression and secretion is induced in response to exercise and activates profound changes in the subcutaneous white adipose tissue (WAT), stimulating expression of uncoupling protein 1 (UCP1) and results in a broad program of brown fat-like development
  55. What is the normal function of PTHrP?
    The normal functions of PTHrP include roles in fetal bone development where it suppresses the maturation of chondrocytes so that the onset of hypertrophic differentiation during endochondral bone growth is delayed
  56. How does Ca regulate PTH secretion?
    • Changes in extracellular fluid calcium ion concentration are detected by a calcium-sensing receptor (CaSR) in parathyroid cell membranes.
    • The CaSR is a G protein-coupled receptor that, when stimulated by calcium ions, activates phospholipase C and increases intracellular inositol 1,4,5 triphosphate and diacylglycerol formation. This stimulates release of calcium from intracellular
    • stores, which, in turn, decreases PTH secretion (by increased proteolysis). Conversely, decreased extracellular fluid calcium ion concentration inhibits these pathways and stimulates PTH secretion
  57. What is the mechanism of action of PTH in osteoporosis?
    • PTH treatment targets osteoblasts to enhance bone remodeling by differentiation of preosteoblast.
    • Increases in bone formation occur more quickly than bone resorption, leading to an increase in lumbar BMD that is greater in the first two years of treatment than any antiresorptive agent. The actions of PTH on skeletal compartments are site-specific (trabecular bone more prominent)
  58. What is the function of calcitonin?
    Calcitonin exerts its hypocalcemic effects primarily through inhibition of osteoclast-mediated bone resorption (reduce osteopontin--> osteoclastic attachment)
  59. How can insulin increase glucose uptake in the liver?
    • because of increased activity of the enzymes glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase (PK), the key regulatory enzymes of glycolysis.
    • The latter effects are induced by insulin-dependent activation of phosphodiesterase, with decreased PKA activity and diminished phosphorylation of the regulatory glycolytic enzymes
  60. Somatostatin act through ...............
    Gi PCR
  61. What is the function of amylin?
    • secreted from β-cells of the pancreas simultaneously with insulin in response to nutrient intake
    • major component of diabetes-associated islet amyloid deposits
    • reduction in the rate of gastric emptying, suppression of food intake, and suppression of post-meal glucagon secretion
  62. Which hormones act through PLC or AC?
    • PLC--> Angiotensin II (vascular smooth muscle), Catecholamines (α receptors), GnRH, GHRH, TRH, oxytocin, Vasopressin (V1 receptor, vascular smooth muscle)
    • AC--> ACTH, LH, FSH, CRH, HCG, TSH, Angiotensin II (epithelial cells), Calcitonin, Catecholamines (β receptors), glucagon, secretin, somatostatin, Vasopressin (V2 receptor, epithelial cells)
  63. What are the main function of AMPK?
    • Once activated, AMPK-mediated phosphorylation events switch cells from active ATP consumption (e.g. fatty acidand cholesterol biosynthesis) to active ATP production (e.g. fatty acid and glucose oxidation). These events are rapidly initiated and are referred to as short-term regulatory processes.
    • The activation of AMPK also exerts long-term effects at the level of both gene expression and protein synthesis.
    • Other important activities attributable to AMPK are regulation of insulin synthesis and secretion in pancreatic islet β-cells and modulation of hypothalamic functions involved in the regulation of satiety.
  64. What is the structure of AMPK?
    • trimeric enzyme composed of a catalytic α subunit and the non-catalytic β and γ subunits. 
    • The N-terminal half of the α subunits contains a typical serine/threonine kinase catalytic domain. Interaction with the β and γ subunits occurs via the C-terminal half of the α subunits.
  65. How is AMPK regulated?
    • In the presence of AMP the activity of AMPK is increased approximately 5-fold. However, more importantly is the role of AMP in regulating the level of phosphorylation of AMPK. An increased AMP to ATP ratio leads to a conformational change in the γ-subunit leading to increased phosphorylation and decreased dephosphorylation of AMPK. The phosphorylation of AMPK results in activation by at least 100-fold.
    • AMPK is phosphorylated by at least three different upstream AMPK kinases (AMPKKs). Phosphorylation of AMPK occurs in the α subunit at threonine
    • serine-threonine kinase, LKB1 (which is encoded by the Peutz-Jeghers syndrome tumor suppressor gene, is required for activation of AMPK in response to stress
    • One kinase activator of AMPK is Ca2+-calmodulin-dependent kinase kinase β (CaMKKβ) which phosphorylates and activates AMPK in response to increased calcium. As described for the Ca2+-mediated regulation of glycogen metabolism, increased release of intracellular stores of Ca2+ create a subsequent demand for ATP. Activation of AMPK in response to Ca fluxes provides a mechanism for cells to anticipate the increased demand for ATP.
  66. The main regulator of AMPK is...............
  67. AMPK is active when............
  68. How is AMPK regulated by AMP?
    • The effects of AMP are two-fold: a direct allosteric activation and making AMPK a poorer substrate for dephosphorylation. Because AMP affects both the rate of AMPK phoshorylation in the positive direction and dephosphorylation in the negative direction, the cascade is ultrasensitive.
    • This means that a very small rise in AMP levels can induce a dramatic increase in the activity of AMPK.
  69. Negative allosteric regulation of AMPK also occurs by .......................
  70. What are the functions of AMPK?
    • Enhance: PFK2 (cardiac glycolysis)/ GLUT1,4 (glucose transport)/ FA oxidation
    • Inhibit: FAS, ACC (FA synthesis)/ HSL (lipolysis)/ HMGCOAR (cholesterol, isoprenoid synthesis)/glycerol-3-phosphate acyltransferase (TG synthesis)/ Glyocgen synthase (Glycogenesis)/ eEF2 mTOR (protein synthesis)
    • Inhibit: beta cell insulin secretion/ FA and cholesterol synthesis in liver/ FA synthesis and lipolysis in adipocytes
    • Enhance: FA oxidation, glucose uptake and glycolysis in heart/ FA oxidation and glucose uptake in skeletal muscle
  71. What are the activators and inhibitors of AMPK?
    • Activator--> metformin, TZD, Leptin (in adipose and liver), Adiponectin, Ghrelin
    • Inhibitor--> resistin, leptin (hypothalamus),  GLP-1, and insulin
  72. the primary function of AMPK is to ....................and, thereby regulate the activity of numerous metabolic enzymes
  73. Which pituitary hormones are GP with two subunit and which are single chain of aminoacids?
    • TSH, FSH, LH-->GP
    • PRL, ACTH, GH--> single
  74. Which hypothalamic hormone is a tripeptide?
  75. What are the stimulator and inhibitor of GH secretion?
    • Stimulate: Decreased blood glucose, Decreased blood free fatty acids, Increased blood amino acids (arginine), Starvation or fasting, protein deficiency, Trauma, stress, excitement, Exercise, Testosterone, estrogen, Deep sleep (stages II and IV), Growth hormone-releasing hormone, Ghrelin
    • Inhibit: Increased blood glucose, Increased blood free fatty acids, Aging, Obesity, Growth hormone inhibitory hormone (somatostatin), Growth hormone (exogenous), Somatomedins (insulin-like growth factors)
  76. What are the actions of TSH?
    • Increased proteolysis of the thyroglobulin
    • Increased activity of the iodide pump (trapping)
    • Increased iodination of tyrosine
    • Increased size and increased secretory activity 
    • Increased number of thyroid cells plus a change from cuboidal to columnar cells and much infolding of the thyroid epithelium into the follicles
  77. What increases and decreases insulin secretion?
    • Enhance: Increased blood glucose, Increased blood free fatty acids, Increased blood amino acids, Gastrointestinal hormones (gastrin, cholecystokinin, secretin, gastric inhibitory peptide), Glucagon, growth hormone, cortisol, Parasympathetic stimulation; acetylcholine, β-Adrenergic stimulation, Insulin resistance; obesity, Sulfonylurea drugs (glyburide, tolbutamide)
    • Inhibit: Decreased blood glucose, Fasting, Somtatostatin, α-Adrenergic activity, Leptin
  78. What are the regulators of glucagon?
    • Inhibit: increased blood glucose, insulin, somatostatin
    • Enhance: increased aminoacid (glucagon then promotes rapid conversion of the amino acids to glucose), exercise 
  79. What are the origin of neurotransmitters?
    • GABA: glutamate
    • Ach: Choline
    • Adenosine: ATP
    • Cathecolamines: tyrosine
    • Melatonin serotonin: tryptophan
    • Histamine: Histidine
    • NO: Arg
    • Anandamide: Phospholipids
  80. ............most abundantly expressed in enterochromaffin cells of the gut
  81. classic response to CB1 activation is .................
    stimulation of food intake
  82. What is the function of adenosine in CNS?
    is an inhibitory neurotransmitter within the CNS, suppresses arousal thus promoting sleep
  83. The link between neurotransmitters and intracellular signaling is carried out by association either with .......................
    the receptor-associated G-protein, with protein kinases, or by the receptor itself in the form of a ligand-gated ion channel
  84. What are the types and functions of glutamate receptor?
    • mGluR--> GPCR (Gi presynpatic or Gq postsynaptic) (LTP and LTD)/  close proximity to the synaptic cleft/ modulate the neurotransmitter effects/ also in the periphery
    • AMPA--> ionotropic (responsible for the bulk of fast excitatory synaptic transmission throughout the CNS)/ low permeability to calcium ions
    • Kainate--> ionotropic/hippocampus/ regulation of synaptic plasticity
    • NMDA--> ionotropicfunctional NMDA receptors requires simultaneous binding of both glutamate and glycine--> calcium influx into the postsynaptic cells

    • Notes: 
    • The GluAMPA2 subunit of the receptor is responsible for regulating the permeability of the channel to calcium ions. The GluA2 mRNA is subject to RNA editing which alters the function of the calcium permeability character of the subunit
  85. What is the mechanism of LTP?
    Glutamate binding to NMDA receptors results in calcium influx into the postsynaptic cells leading to the activation of a number of signaling cascades. These signaling cascades can include activation of calcium/calmodulin-dependent kinase II (CaMKII) leading to phosphorylation of the GluA2 AMPA receptor subunit. This latter effect results in long-term potentiation (LTP).
  86. What is the glutamine glutamate cycle in the brain?
    • Ammonium ion (NH4+) in the blood is taken up by astrocytes and incorporated into glutamate via glutamine synthetase.
    • The glutamine then is transported to presynaptic neurons via sodium-coupled neutral amino acid transporter, SNAT7.
    • Within the presynaptic neuron glutamate is formed from the glutamine via the action of glutaminase. The glutamate is packaged in secretory vesicles for release following activation of an action potential. Glutamate in the synaptic cleft can be taken up by astrocytes via a Na dependent system. Within the astrocyte the glutamate is converted back to glutamine.
    • A portion of the glutamate can be oxidized within the nerve cells following transamination. The principle transamination reaction involves aspartate aminotransferase (AST) and yields α-ketoglutarate (2-oxoglutarate) which is a substrate in the TCA cycle
    • This reaction also buffer ammonia in the brain
  87. What are the steps in the synthesis of GABA?
    • Glucose is the principal precursor for GABA production via its conversion to α-ketoglutarate in the TCA cycle.
    • Within the context of the GABA shunt, the α-ketoglutarate is transaminated to glutamate by GABA α-oxoglutarate transaminase (GABA-T). Glutamic acid decarboxylase (GAD) catalyzes the decarboxylation of glutamic acid to form GABA
    • The activity of GAD requires pyridoxal phosphate (PLP) as a cofactor. PLP is generated from the B6 vitamins through the action of pyridoxal kinase. Pyridoxal kinase itself requires zinc for activation
  88. .............is the principal precursor for GABA production via its conversion to .............. in the TCA cycle
    Glucose/ α-ketoglutarate
  89. Glutamic acid decarboxylase is required for .......synthesis and requires .....as cofactor
    GABA/ pyridoxal phosphate
  90. What are the functions of GABA receptors?
    • GABAA--> ionotropic--> reduced dendritic excitatory glutamatergic responses as a consequence of a local increase in conductance across the plasma membrane.
    • GABAB--> GPCR--> open K channels in the post-synaptic or close Ca channels in presynaptic
  91. What are the receptors of Ach?
    • M-->GPCR
    • M1,3,5: Gq
    • M2,4: Gi
    • N (pentamer)--> N,M (ionotropic)--> influx of Na, efflux of K
    • M: desensitize in response to GRK/ N: in response to PKA or PKC
  92. What is α-Latrotoxin?
    • protein produced by the black widow spider
    • induces massive ACh release, possibly by acting as a Ca2+ ionophore
  93. PNMT requires .............. as cofactor and produces .......from..............
    S-Adenosylmethionine/ Epinephrine/ Norepinephrine
  94. Tyrosine hydroxylase requires ...........as cofactor
  95. What are the types of cathecolamine receptors?
    • Alpha1, (D5)--> Gq
    • Alpha, D2,3,4--> Gi
    • Beta, D1,5--> Gs
  96. How is catecholamine metabolism?
    • 1
  97. List the receptor of each neurotransmitter
    • M1--> Excitatory;  reduces K+ conductance; increases IP3 and DAG
    • M2--> Inhibitory; increased K+ conductance; reduced cAMP
    • N-> Excitatory; increased cation conductance
    • D1--> Inhibitory; increased cAMP
    • D2--> Inhibitory (presynaptic); reduces Ca2+ conductance
    • D2--> Inhibitory (postsynaptic); increased K+conductance;  reduced cAMP
    • Alpha1--> Excitatory;  reduced K+ conductance; increased IP3 and DAG
    • Alpha2--> Inhibitory (presynaptic);  reduces Ca2+conductance
    • Alpha2--> Inhibitory (postsynaptic);  enhance K+conductance;  reduces cAMP
    • B1-> Excitatory; reduced  K+ conductance; increased cAMP
    • Beta2--> Inhibitory;  enhance electrogenic sodium pump
    • GABAA--> Inhibitory;  increasedCl– conductance
    • GABAB-->Inhibitory (presynaptic);  reduces Ca2+conductance/ Inhibitory (postsynaptic);  increases K+conductance
    • Iontropic glutamate--> Excitatory;  increased Ca2+ or cation conductance
    • Metabotropic glutamate: Inhibitory (presynaptic);  reduces Ca2+conductance reduces cAMP / Excitatory (postsynaptic);   reduces K+conductance,  increases IP3 and DAG
    • Glycine--> Inhibitory;increases  Cl– conductance
    • Opioid--> Inhibitory (presynaptic);   Reduces Ca2+conductance;  reduces cAMP/ Inhibitory (postsynaptic);  increases K+conductance;  reduces cAMP
    • 5HT1A: Inhibitory; increased K+ conductance
    • 5HT2A: Excitatory; reduces K+ conductance; increases IP3 and DAG
    • 5HT3: Excitatory; increased  cation conductance
    • 5HT4: Excitatory; reduces K+ conductance; increases cAMP
  98. D2, Alpha2, GABA-B, and opioids all inhibit...........
    • presynaptic; reduces Ca2+ conductance
    • postsynaptic ; increased K+conductance (also reduces cAMP in D2 , alpha2,opioid)
  99. What are some drugs with selective action on neurotransmitter receptors?
    • D1 agonist: Fenoldopam
    • D1 antagonist: phenothiazine
    • D2 agonist: Bromocriptine, pergolide, cabergoline, ropinirole
    • D2 antagonist: Haloperidol, raclopride, sulpiride, risperidone, phenothiazine
    • D3 agonist: pramipexole, rotigotine
    • M1 antagonist: pirenzepine and atropine
    • M2 antagonist: Atropine
    • 5-HT 1A; buspirone is a partial agonist 
    • 5-HT1D AGONISTS: Triptan
    • 5-HT2A; blocked by clozapine, risperidone, and olanzapine
    • 5-HT2 antagonist: Ketanserin (for HTN and carcinoid)
    • 5-HT3; blocked by ondansetron
    • 5HT4 partial agonist: Tegaserod
    • GABAA; facilitated by benzodiazepines and zolpidem
    • GABAB; activated by baclofen
    • NMDA antagonist: phencyclidine, ketamine, and memantine
    • Glycine antagonist: strychnine
  100. Serotonin (5-hydroxytryptamine, 5HT) is formed by the ....................... of tryptophan
    hydroxylation and decarboxylation
  101. What are the enzymes involved in serotonin synthesis from tryptophan?
    • tryptophan hydroxylase (requires THB)
    • and aromatic L-amino acid decarboxylase
  102. What are the actions by 5HT receptors?
    • 1--> Gi: inhibits cAMP production, inhibitory neurotransmission
    • 2-->Gq: increased production of DAG and IP3, excitatory neurotransmission
    • 3--> ligand-gated Na+ and K+ channels: depolarizes axonal membrane, excitatory neurotransmission
    • 4--> Gs: increases cAMP production, excitatory neurotransmission
  103. Which 5HT receptor is a ligand gated ion channel?
  104. Within vesicles, norepinephrine and epinephrine are bound to .....................
    ATP and chromogranin A.
  105. How is melatonin synthesized?
    • Pathway for serotonin and melatonin synthesis from tryptophan. Abbreviations: THP = tryptophan hydroxylase, DHPR = dihydropteridine reductase, H2B = dihydrobiopterin, H4B = tetrahyrobiopterin, 5-HT = 5-hydroxytryptophan, AADC = aromatic L-amino acid decarboxylase, SNA = serotonin N-acetylase, HOMT = hydroxyindole-O-methyltransferase
  106. Melatonin is formed in the ................. where............... is present
    Retina and pineal/hydroxyindole-O-methyltransferase
  107. ....................... activate the N-acetyltransferase required for melatonin synthesis
    NE secreted on the pineal increases levels of cAMP and thuse
  108. What are the location for each 5HT receptor?
    • 5HT1D: Brain
    • 5HT2: Smooth muscle, platelets (mediates carcinoid syndrome)
    • 5HT3: Area postrema (CNS), sensory and enteric nerves
    • 5HT4: Presynaptic nerve terminals in the enteric nervous system
    • 5HT2A receptors mediate platelet aggregation and smooth muscle contraction. The 5HT2C receptors are suspected in control of food intake as mice lacking this gene become obese from increased food intake (fenfluramine/ an agonist was used for weight reduction)
  109. What are the symptoms of NMS/ Serotonin syndrome/ MH/ and Cholinergic crisis?
    • NMS--> evolve in 1-3 days/ tetrad of Mental status change, lead pipe rigidity, hyperpyrexia, ANS including diaphoresis (profuse), reduced or normal bowel sound
    • Serotonin--> Onset within hours, Hyperthermia, hyperreflexia, tremor, clonus, hypertension, hyperactive bowel sounds, diarrhea, mydriasis, agitation, coma. Typical features in these patients that are not often seen in NMS patients are shivering, hyperreflexia, myoclonus, and ataxia and prodrome of N,V, and diarrhea
    • MH--> Onset in minutes, like NMS in the context of halogenated anesthetic or succinylcholine
    • Anticholinergic--> no diaphoresis, rigidity or elevated CK
  110. What is the treatment of NMS, MH, Serotonin syndrome?
    • NMS: cooling+Withdrawal dantrolene, bromocriptine, and/or amantadine, Diphenhydramine, (parenteral)
    • Serotonin: Withdrawal, supportive, intubation, paralysis, BZD, Cyproheptadine (a histamine-1 receptor antagonist with nonspecific 5-HT1A and 5-HT2A antagonistic)
    • MH: Dantrolene, cooling
  111. Which agents are associated with serotonin syndrome?
    SSRIs, second-generation antidepressants, MAOIs, linezolid, tramadol, meperidine, fentanyl, ondansetron, sumatriptan, MDMA, LSD, St. John's wort, ginseng
  112. How are creatine and creatinine synthesized?
    • Arg+Gly--> guanidoacetate+SAM--> Creatine+ATP--> Creatine phsphate--> creatinine
    • Creatine is synthesized in the liver by methylation of guanidoacetate using SAM as the methyl donor. Guanidoacetate itself is formed in the kidney from the amino acids arginine and glycine
    • The phosphate of ATP is transferred to creatine, generating creatine phosphate, through the action of creatine phosphokinase
    • Creatinine is formed in muscle from creatine phosphate by a nonenzymatic dehydration and loss of phosphate

  113. Glutathione (abbreviated GSH) is a tripeptide composed of .............................
    glutamate, cysteine and glycine
  114. What are the functions of GSH?
    Glutathione serves as a reductant; is conjugated to drugs to make them more water soluble; is involved in amino acid transport across cell membranes (the γ-glutamyl cycle); is a substrate for the peptidoleukotrienes; serves as a cofactor for some enzymatic reactions and as an aid in the rearrangement of protein disulfide bonds. GSH is synthesized in the cytosol of all mammalian cells
  115. The rate of GSH synthesis is dependent upon the availability of ......... and the activity of the rate-limiting enzyme, ............................
    cysteine/γ-glutamylcysteine synthetase (GCS)
  116. Endogenously produced hydrogen peroxide (H2O2) is reduced by GSH in the presence of ................
    selenium-dependent GSH peroxidase
  117. What is the gamma-glutamyl cycle?
    The γ-glutamyl cycle is an example of a group transfer mechanism of amino acid transport. Although this mechanism requires more energy input, it is rapid and has a high capacity. The cycle functions primarily in the kidney, particularly renal epithelial cells. The enzyme γ-glutamyl transpeptidase is located in the cell membrane and shuttles GSH to the cell surface to interact with an amino acid. Reaction with an amino acid liberates cysteinylglycine and generates a γ-glutamyl-amino acid which is transported into the cell and hydrolyzed to release the amino acid.
  118. How does acetylcholine and bradykinin exert their vasodilator effect?
    • Vasodilators, such as acetylcholine and bradykinin, do not exert their effects upon the vascular smooth muscle cell in the absence of the overlying endothelium.
    • When acetylcholine (or bradykinin) binds its receptor on the surface of endothelial cells, a signal cascade, coupled to the activation phospholipase C-γ (PLCγ), is initiated.
    • The PLCγ-mediated release of inositol trisphosphate, IP3 (from membrane associated phosphatidylinositol-4,5-bisphosphate, PIP2), leads to the release of intracellular stores of Ca2+.
    • In turn, the elevation in Ca2+ leads to the liberation of endothelium-derived relaxing factor (EDRF) which then diffuses into the adjacent smooth muscle.
    • Within smooth muscle cells, EDRF reacts with the heme moiety of a soluble guanylyl cyclase, resulting in activation of the latter and a consequent elevation of intracellular levels of cGMP.
    • The net effect is the activation of cGMP-dependent protein kinase (PKG) and the phosphorylation of substrates leading to smooth muscle cell relaxation.
    • The coronary artery vasodilator, nitroglycerin, acts to increase intracellular release of EDRF and thus the activation of the cGMP signal cascade
  119. How is NO formed by NOS?
    arginine ——> citrulline + NO
  120. What is the structure of NOS?
    • Neuronal NOS (nNOS), also called NOS-1
    • Inducible or macrophage NOS (iNOS), also called NOS-2
    • Endothelial NOS (eNOS), also called NOS-3.
    • NOS has five redox cofactors: NADPH, FAD, FMN, heme and tetrahydrobiopterin (H4B).
    • NO can also be formed from nitrite, derived from vasodilators such as glycerin trinitrate (nitroglycerin) during their metabolism.
    • The half-life of NO is extremely short, lasting only 2-4 seconds. This is because it is a highly reactive free radical and interacts with oxygen and superoxide.
    • NO is inhibited by hemoglobin and other heme proteins which bind it tightly
  121. How is NOS regulated?
    • Both eNOS and nNOS are constitutively expressed and regulated by Ca2+.
    • The calcium regulation is imparted be the associated calmodulin subunits, thus explaining how vasodilators such as acetylcholine effect smooth muscle relaxation as a consequence of increasing intracellular endothelial cell calcium levels.
    • Although iNOS contains calmodulin subunits, its activity is unaffected by changes in Ca2+ concentration.
    • iNOS is transcriptionally activated in macrophages, neutrophils, and smooth muscle cells.
    • The major functions of NO production through activation of iNOS are associated with the bactericidal and tumoricidal actions of macrophages.
    • Overproduction of NO via iNOS is associated with cytokine-induced septic shock such as occurs post-operatively in patients with bacterial infections.
    • Bacteria produce endotoxins such as lipopolysaccharide (LPS) that activate iNOS in macrophages