Updated: 9/21/2019

G Protein-Coupled Receptors (GPCR)

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Overview
  • G protein-coupled receptors (GPCR) 
    • 7 transmembrane domain receptors on the cell membrane that sense the external environments
    • ligands activate the G protein by causing a conformational change
    • this change propagates to a second messenger which detaches from the GPCR to carry the signal to other effector proteins
  • 3 types of GPCR second messengers and functions
    • Gq activates phospholipase which results in the formation of
      • inositol phosphate (IP3) → ↑ [Ca2+]
      • diacylglycerol → activation of protein kinase C (PKC)
      • examples of receptor types: α1, H1, V1, M1, M3
    • Gs activates adenyl cyclase resulting in  
      • ↑ cAMP → ↑ activity of protein kinase A (PKA)
      • examples of receptor types: β1, β2 , D1, H2, V2
    • Gi inhibits adenyl cyclase resulting in 
      • ↓ cAMP → ↓ activity of protein kinase A (PKA)
      • examples of receptor types: α2, D2, M
Receptor Types
 
Receptor
GPCR Class Locations and Major Functions 
Adrenoceptor: Sympathetic System
α1 q
  • GI and GU: contraction of sphincters
  • Eye: contraction of iris radial muscle (mydriasis)
  • Vasculature: vasoconstriction
α2 i
  • GI: ↓ motility
  • Vasculature: vasoconstriction of veins and arteries in heart BUT vasodilation of arteries
  • Presynaptic adrenergic nerve terminals: ↓ sympathetic outflow by inhibiting NE release
  • Lipocytes: ↓ decreases lipolysis
  • Pancreas: ↓ insulin and ↑ glucagon
  • Platelets: stimulation of platelet aggregation
β1 s
  • Heart: positive chronotrope and inotrope
  • Kidney: ↑ renin release
  • Lipocytes: ↑ lipolysis
β2 s
  • Vasculature: vasodilation (specifically skeletal muscle vasculature)
  • Lung: bronchodilation
  • GI and GU: bladder and uterus relaxation
  • Heart: positive inotrope and chronotrope
  • Eye: ciliary muscle relaxation
  • Lipocytes: ↑ lipolysis
  • Pancreas: ↑ insulin release
  • Liver: ↑ gluconeogenesis and glycogenolysis
Cholinoreceptors: Parasympathetic System
M1 q
  • CNS: excitatory in the CNS
  • Glands: ↑ salivary, sweat, and stomach secretions
M2 i
  • Heart: negative chronotrope and ↓ contractility of atria
M3 q
  • Glands: ↑ salivary, sweat, stomach glands
  • GI and GU: ↑ motility, ↑ bladder and uterus contraction
  • Lung: bronchoconstriction
  • Eye: ciliary and iris circular muscle contraction
Dopaminergic Receptors
D1 s
  • Kidney: renal vascular smooth muscle relaxation
D2 i
  • Brain: modulates neurotransmitter release
Other G Protein-Coupled Receptors (Histamine and Vasopressin)
H1 q
  • Glands; ↑ nasal and bronchial mucus secretion
  • Lung: bronchoconstriction
  • Skin: pruritus (itching), ↑ pain and irritation
H2 s
  • GI: ↑ gastric acid secretion
V1 q
  • Vasculature: vasoconstriction
V2 s
  • Kidney: antidiuretic, ↑ water permeability and reabsorption in the collecting tubules
 

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Questions (5)
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(M1.PH.17.4817) A 5-year-old boy is brought to the emergency department by his parents for difficulty breathing. He was playing outside in the snow and had progressive onset of wheezing and gasping. His history is notable for eczema and nut allergies. The patient has respirations of 22/min and is leaning forward with his hands on his legs as he is seated on the table. Physical examination is notable for inspiratory and expiratory wheezes on exam. A nebulized medication is started and begins to relieve his breathing difficulties. Which of the following is increased in this patient as a result of this medication? Tested Concept

QID: 109407
1

Diacylglycerol

4%

(4/97)

2

Cyclic GMP

19%

(18/97)

3

Cyclic AMP

70%

(68/97)

4

Protein kinase C

5%

(5/97)

5

ATP

2%

(2/97)

L 3 B

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(M1.PH.13.115) A 23-year-old woman presents to the emergency department with acute onset of shortness of breath, wheezing, and chest tightness. This is her 4th visit for these symptoms in the last 5 years. She tells you she recently ran out of her normal "controller" medication. Concerned for an asthma exacerbation, you begin therapy with a short-acting beta2-agonist. What is the expected cellular response to your therapy? Tested Concept

QID: 100631
1

Gs protein coupled receptor activates adenylyl cyclase and increases intracellular cAMP

76%

(178/233)

2

Gs protein coupled receptor activates phospholipase C and increases intracellular calcium

5%

(11/233)

3

Gq protein coupled receptor activates phospholipase C and increases intracellular calcium

3%

(8/233)

4

Gq protein coupled receptor activates adenylyl cyclase and increases intracellular cAMP

8%

(18/233)

5

Gi protein coupled receptor inhibits adenylyl cyclase and decreases cAMP

6%

(14/233)

L 1 E

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