Updated: 5/18/2019

G Protein-Coupled Receptors (GPCR)

Review Topic
  • 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, M2
Receptor Types
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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Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2

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(M1.PH.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? Review Topic

QID: 109407





Cyclic GMP




Cyclic AMP




Protein kinase C








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(M1.PH.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? Review Topic

QID: 100631

Gs protein coupled receptor activates adenylyl cyclase and increases intracellular cAMP




Gs protein coupled receptor activates phospholipase C and increases intracellular calcium




Gq protein coupled receptor activates phospholipase C and increases intracellular calcium




Gq protein coupled receptor activates adenylyl cyclase and increases intracellular cAMP




Gi protein coupled receptor inhibits adenylyl cyclase and decreases cAMP




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