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PHARMACOLOGY > 06-Cellular Reception and Drug Action > Flashcards

06-Cellular Reception and Drug Action Flashcards

1
Q

What is a G-protein?

A

Protein that stimulates effectors to produce intracellular changes

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2
Q

What are the G-protein subgroups?

A

Gs, Gi and Gq

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3
Q

What is Gs?

A

Stimulatory

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4
Q

What is Gi?

A

Inhibitory

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5
Q

What is Gq?

A

We don’t know what these do

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6
Q

How is our ability to see light and smell linked with these g-protein coupled receptors?

A
  • Receptors that interact with the G-proteins include those for light, odorants, hormones, neurotransmitters and prostaglandins
  • Ability to see light and smell are all involved in complex biological processes
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7
Q

What does the binding of a ligand to its receptor cause?

A

Causes the g-protein to stimulate an effector

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8
Q

What are some examples of effectors?

A 
Ion channels:
- Ex. cardiac muscarinic receptor
Adenylyl cyclase:
- This enzyme makes cAMP from ATP
- cAMP is a second messenger (involved in the cAMP signal transduction pathway)
Phospholipase C (PLC):
- PLC acts to cleave PIP
- THe cleaved PIP yields IP3 and DAG
- IP3 and DAG are both second messengers (involved in the phophatidylinosital signal transduction pathway)
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9
Q

Muscarinic receptors are…?

A

Cholinergic -> Acetylcholine is their endogenous ligand

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10
Q

Adenylyl cyclase is always associated with…?

A

Gs and Gi

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11
Q

Phospholipase C is always associated with…?

A

Gq

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12
Q

Ligand binding at a receptor site leads to what?

A

G-proteins will then stimulate an effector

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13
Q

Cardiac Atrial Muscarinic Receptor

A
  • Coupled to a G-protein that is connected to a K+ channel
  • When acetylcholine binds to the muscarinic receptor the associated G-protein is stimulated
  • The G-protein activates the K+ channel to open
  • K+ leaves the cell, hyperpolarizing the cellular membrane and slowing the heart rate
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14
Q

Muscarinic receptors are associated with…?

A

Parasympathetic nervous system, rest, rumination, relaxation and reproduction

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15
Q

G-proteins linked to adenylyl cyclase: How does the Gs protein link to it?

A
  • Stimulates Adenylyl cyclase
  • Adenylyl cyclase converts ATP into cAMP
  • cAMP is a second messenger that binds to and activates protein kinases
  • Protein kinases activate enzymes by adding a phosphate group
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16
Q

G-proteins linked to adenylyl cyclase: How does the Gi protein link to it?

A
  • Inhibits adenylyl cyclase
  • Activation of Gi leads to a decrease in cAMP since no new cAMP is made
  • Less protein kinases, less intracellular phosphorylation
  • Shifts can lead to greater/lesser physiological response
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17
Q

When an agonist binds to a receptor what happens?

A

Stimulates Gs protein, stimulates AC then increases cAMP, activates protein kinases and leads to biological effects. COMPLEX PROCESS

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18
Q

What is albuterol/salbutamol?

A
  • Bronchodilator
  • Specific beta2-adrenergic receptor agonist
  • Binding to the receptor activates adenylyl cyclase via the Gs protein
  • Increase in cAMP causes the activation of enzymes that sequester calcium
  • Decreased calcium levels lead to relaxation of the bronchial smooth muscle
  • Increase in cAMP causes an increase in protein kinases, enzyme phosphorylizes the pump, brings calcium into the sarcoplasmic reticulum, less calcium in smooth muscle and leads to relaxation
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19
Q

Why are calcium levels important to muscle contraction?

A
  • More calcium = more muscle contraction

- Less calcium = less muscle contraction

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20
Q

When we give an agonist to a receptor associated with Gs, what is the net biological effect?

A

Inhibitory, it inhibits muscle contraction

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21
Q

Gi linked to adenylyl cyclase: Misoprostol (peptic ulcer drug)

A
  • Prostaglandin E1 receptor in the gut
  • Misoprostol binds to the E1 receptor, stimulates the Gi protein, inhibits AC, decreases cAMP, less phosphorylation, enzymes in pump producing stomach acid are no longer active
  • Protective for ulcer
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22
Q

Why is misoprostol not to be given to pregnant patients?

A

Binds to EP3 in uterus, decrease cAMP, increase of calcium, therefore muscle contractions occur in the uterus. This can cause spontaneous miscarriage, can be used for pharmacological abortion

23
Q

How is G1 linked to phospholipase C?

A
  • PLC activated by Gq
  • PLC cleaves PIP
  • Cleaved PIP yields 2nd messengers (IP3 and DAG)
  • IP3 binds to the sarcoplasmic reticulum and stimulates the release of calcium into the cytoplasm (IP3 activates pumps associated with Ca+, reverses it, moves calcium into the cytosol to facilitate contraction)
  • Calcium influx into the cytoplasm produces the biological response
24
Q

How is Gq linked to phospholipase C?

A
  • Ergonovine binds to Gq protein linked prostaglandin E1, receptors in the uterus and Gq proteins linked a1 adrenoceptors in the blood vessels
  • Receptors binding stimulates PLC to produce IP3 and DAG
  • IP3 binds to the sarcoplasmic reticulum and induces release of calcium into the cytoplasm
  • Induces contraction of the uterus and blood vessels
25
Q

Why must the uterus continue to contract post delivery?

A

Promote formation of therapeutic clots to stop blood flow

26
Q

Ergonovine is not specific for EP1 and also has affinity for A1 in the vasculature

A

Causes vasoconstriction and increases blood pressure. Need to monitor patient for hypertensive crisis

27
Q

Why do we give an IM injection of oxytocin after birth?

A

Bypass worry all together, the uterus will contract and save the patients life

28
Q

T/F: the endogenous ligand is water soluble for intracellular receptors
(if F, correct)

A
  • F

- ligand is always fat soluble

29
Q

T/F: on membrane spanning enzymes, the endogenous ligand stimulates the receptor
(if F, correct)

A

-TRUE

30
Q

T/F: G-protein coupled receptors activate G-proteins which activates an effector activating protein kinases
(if F, correct)

A

-TRUE

31
Q

Give 4 examples of receptors that interact with G-proteins…

A
  • odorants
  • hormones (water soluble)
  • neurotransmitters
  • prostaglandins
32
Q

With what receptor is the Gprotein effector an ion channel (give an example)?

A

-cardiac muscarinic receptor

33
Q

What is always the ligand for a muscarinic receptor?

A

acetyl choline

34
Q

Describe the use of a Gprotein with the cardiac atrial muscarinic receptor…

A
  • ACh binds to the receptor, stimulating the Gprotein
  • Gprotein activates the K channel to open
  • K leaves the cell, hyperpolarizing the membrane to slow HR
35
Q

T/F: all G proteins use adenylyl cyclase as the effector…

if F, correct

A
  • F
  • only Gs and Gi use adenylyl cyclase
  • Gq uses PLC
36
Q

Explain the process of Gs proteins

A
  • effector is stimulated by binding of endogenous ligand
  • adenylyl cyclase turns ATP into cAMP
  • cAMP activates protein kinases which in turn yields the biological effect
37
Q

T/F: cAMP is a 2nd messenger for protein kinases.

if F, correct

A

-TRUE

38
Q

By which mechanism are protein kinases activated?

A

-cAMP uses enzymes to phosphorylate (add phosphate) to the protein kinases

39
Q

T/F: stimulating Gs proteins always result in the cell doing more of something
(if F, correct)

A
  • F

- stimulating Gs could also result in the cell doing less

40
Q

How is the Gi process different from the Gs?

A
  • Gi inhibits the effector (adenylyl cyclase)

- less cAMP and less phosphorylation of protein kinases

41
Q

Explain the process of albuterol (a bronchodilator) using the Gs pathway

A
  • activate effector
  • increased cAMP activates enzymes that sequester Ca (smooth muscle) and inactivate MLCK leading to smooth muscle relaxation
42
Q

T/F: administering through an IV makes it harder to target just one tissue for the drug to effect.
(if F, correct)

A

-TRUE

43
Q

Why would it be dangerous to administer ventolin (used for bronchodilation) using an IV for a woman in labour?

A
  • uses the Gs pathway
  • Gs in many different tissues, the IV would not specify which tissue to have an effect
  • would shut down the labour as it relaxes smooth muscle
44
Q

Explain the process of misoprostol (peptic ulcer drug) using the Gi protein system

A
  • cAMP decreases
  • protein kinases not activated (less stomach acid produced and pumped)
  • stomach mucosa now has less acid and can heal itself
45
Q

T/F: You should never give msioprostol to someone who is pregnant…
(if F, correct)

A
  • TRUE

- causes uterine contraction!!

46
Q

Explain the Gq protein system

A
  • Gq protein activates the effector of phospholipase C (PLC)

- PLC cleaves PIP and yields 2 2nd messengers (IP3 and DAG)

47
Q

What effect does the 2nd messenger of IP3 have?

A

-binds to the sarcoplasmic reticulum and stimulates the release of Ca into the cytoplasm (increase Ca in smooth muscle)

48
Q

What effect does the 2nd messenger of DAG (diacylglycerol) have?

A

-binds to Ca channels on cell membrane, facilitates the movement of extracellular Ca into the smooth muscle cell

49
Q

When is the drug ergonovine used?

A
  • to reduce the risk of post-partum hemmorhage (after the birth; helps to push out the placenta)
  • normally only used in developing countries
50
Q

Explain the process of administered ergonovine using the Gq pathway..

A
  • after birth
  • Gq stimulates PLC to cleave PIP and yield IP3 and DAG
  • IP3 and DAG cause more Ca in the cytoplasm of cell; causing uterine and BV contraction
51
Q

What naturally occurring hormone contracts the uterus?

A

-oxytocin

52
Q

Why is the mother urge to breastfeed the baby as soon as possible after birth?

A
  • feeding releases oxytocin which naturally contracts the uterus and helps to push out the placenta
  • reduce risk of hemmorhage
53
Q

What is normally administered intramuscularly no matter the blood flow at birth?

A

oxytocin!

54
Q

Why is ergonovine a dangerous drug? why is it still used in some countries?

A
  • oxytocic drugs only have eyes for the uterus but ergonovine contracts everything (BP skyrockets)
  • CHEAPER than oxytocic drugs

PHARMACOLOGY (27 decks)

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