Drug Receptor Interactions

Question 1

“Drug”

Answer 1

A chemical substance that interacts with a biological system to produce a physiological effect.

Question 2

Name possible drug target sites

Answer 2

1. Receptors
2. Ion Channels
3. Transport systems
4. Enzymes

= Proteins

Question 3

Receptors as drug target sites

Answer 3

Proteins within cell membranes (usually)
Activated by NT or hormone
Defined by agonists & antagonists
4 types of receptors

Drug examples: ACh (agonist) or Atropine (antagonist)

Question 4

Ion Channels as drug target sites

Answer 4

Selective pores - allow transfer of ions down electrochemical gradients
2 types 1) voltage-sensitive e.g. VSCC
2) receptor-linked e.g. nAChR

Examples: LAs or Calcium Channel blockers

Question 5

Transport systems as drug target sites

Answer 5

Transport against concentration gradients (glucose, ions, NTs)
Specificity for certain species
Examples :Na+/K+-ATPase
: NA ‘uptake 1’

Examples of drugs : Tricyclic anti- depressants (TCAs)
: Cardiac glycosides

Question 6

Enzymes as drug target sites

Answer 6

Catalytic proteins -  rate of reactions
Drug interactions:-
i) enzyme inhibitors
e.g. anticholinesterases (neostigmine) ii) false substrates
e.g. methyldopa
iii) prodrugs
e.g. chloral hydrate -> trichloroethanol

N.B. Unwanted effects e.g. paracetamol

Question 7

Non specific drug actions

Answer 7

Physiochemical properties

e. g. antacids, osmotic purgatives
n. b. Plasma Protein Binding (PPB)

Question 8

What does the potency of a drug depend on?

Answer 8

Efficacy (‘intrinsic activity’) and Affinity

Question 9

What are types of agonists?

Answer 9

Full agonist

Partial agonist -> antagonist activity

Question 10

Drug receptor interactions

Answer 10

Selectivity

Structure-activity relationship
 ‘lock and key’
 agonists  antagonists
 pharmacokinetics

Agonist (ACh; nicotine)

Antagonist (atropine; hexamethonium)

‘Potency’ of a drug depends on:
i) Affinity
ii) Efficacy (‘intrinsic activity’)
 conformational change of receptor

Question 11

What properties of potency do antagonists have?

Answer 11

They have affinity but no efficacy

Question 12

What are the 2 types of receptor antagonists?

Answer 12

Competitive and Irreversible

Question 13

Competitive receptor antagonist

Answer 13

 same site as agonist
 surmountable
 shifts D-R curve to right

Examples: atropine, propranolol

Question 14

Irreversible receptor antagonist

Answer 14

 binds tightly or at different site
 insurmountable

Example : hexamethonium

Question 15

Draw a diagram comparing a full and partial antagonist

Answer 15

-

Question 16

Draw a diagram comparing an agonist alone, a competitive antagonist and an irreversible antagonist.

Answer 16

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