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Flashcards in Endocrinology Deck (659)
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61

Describe the structure of a receptor which is acting as an ion channel

  • 5 membrane-integrated domains
  • Ligand binding site on the EC side
  • 2x alpha subunits
  • 2x beta subunits
  • 1x delta subunit

62

Give examples of receptors which are ion channels

  • n-ACh-R (Nicotinic acetylcholine receptor)
  • Glutamate receptors
  • Anion receptors

63

Nicotinic acetylcholine receptors can be inhibited by...

d-tubocurarine

64

n-ACh-R can be stimulated/inhibited by substances affecting the...

Receptor's 5 subunits

65

What are the states n-ACh-R can be in?

  • Closed (before ACh binding)
  • Open (After ACh binding)

66

Describe the processes after ACh binds to the receptor

  1. Conformational change
  2. Cation channel opens ("open state")
  3. Flow of cations
  4. Local excitatory potential formed
  5. AP is triggered

67

Describe the closing of n-ACh-R

  1. The open channel becomes inactivated
  2. Ligand bond still exists
  3. Change of conformation doesn't allow cation flow
  4. Channel is "inactive"
  5. Dissociation of the ligand
  6. Channel closes

68

Give the main groups of glutamate-sensitive receptors

  • NMDA receptor
  • AMPA receptor
  • Kainate-receptor

69

NMDA receptor

  • Function

N-metil-D-aspartate

  • Binding Mg2+ keeps receptor closed
  • Mg2+ dissociated after receptor activation
  • Ca2+ influx maintains a lasting effect

 

70

Opening of anion-receptors causes

Hyperpolarisation of CNS inhibitory synapses

71

What can cause hyperpolarisation of anion receptors

Nonspecific anions

  • Cl-
  • HCO3-

72

Give the main mediators of anion-receptors

  • GABA
  • Glycine

73

The function of GABA in the anion-receptor

  • Either GABA-A / GABA-B
  • GABA-B activation:
    • Decrease IC cAMP
    • Affects K+ channels

 

74

G-protein structure

  • 3 subunits form a complex:
    • Alpha subunit + GDP
    • Beta subunit
    • Gamma subunit

75

G-protein mechanism of action

  1. The ligand binds to the EC receptor
  2. Conformational change in the 7-M protein
  3. Beta + gamma subunits bind to the IC side of the receptor
  4. Alpha subunit conformational change
  5. Alpha subunit binds GTP
  6. Alpha subunit-GTP complex liberated
  7. Stimulates/inhibits ion channel/enzyme

76

Describe the return of G-protein to its resting state

  1. GTP → GDP
  2. Alpha subunit binds to gamma + beta again
  3. G protein → Resting state

77

Describe Gs effect

  • Activated G-protein migrates to a remote ion channel protein
  • Activates the channel

78

Describe Gi effect

  • Activated G-protein migrates to a remote ion channel protein
  • Inactivates the channel

79

  1. M2 ACh-R
  2. K+ channel opens

80

  1. alfa2 type R
  2. K+ channel opens

81

  1. D2 type R
  2. K+ channel opens

82

  1. GABA type R
  2. Kchannel opens

83

  1. S2 type R
  2. K+ / Ca2+ channel opens

84

  1. OP type R
  2. Ca2+ channel opens

85

Title this figure

Adenylate cyclase mechanism

86

Summarise the adenylate cyclase mechanism

  • Influenced by G-proteins
  • Gs: adenylate cyclase activity ↑
  • Gi: adenylate cyclase activity ↓

87

Describe the steps of the Gs mechanism

  1. Glucagon mobilises Gs G-protein
  2. Liberates hepatic glycogen stores

88

Describe the steps of the Gi mechanism

  • alpha2-adrenergic receptor activated
  • IC cAMP levels ↓

89

List receptors of the Gs pathway

  • Prostacyclin
  • Dopamine D1
  • Catecholamine beta
  • Anterior pituitary
  • Histamine H2
  • 2-type ADH

90

List receptors of the Gi pathway

  • Dopamine D2
  • Alpha1 catecholamine
  • Some glutamate
  • Some opioid