Receptors, agonists and antagonists

Question 1

Law of mass action

Answer 1

The rate of the reaction is proportional to the concentration of the reactants

Question 2

Hill Langmuir Equation

Answer 2

pAR or y= [A]/ Ka + [A]

Question 3

partial agonists

Answer 3

cannot elicit maximum response ( in the absence of spare receptors)

Question 4

partial agonist at musc receptors

Answer 4

pilocarpine

Question 5

partial agonist at histamine H2 rec

Answer 5

impromidine

Question 6

partial agonists at beta rs

Answer 6

prenalterol, full: adrenaline

Question 7

The EC50 of agonists in tissues vary because of differences in ..

Answer 7

receptor densities and the ability of the receptor to activate the receptor (subtype)= agonist efficacy
and maybe tissue specific factors like the presence of degrading enzymes

Question 8

Ka

Answer 8

measure of affinity : k=1/k-1

Question 9

E

Answer 9

measure of efficacy: forward rate(k+2)/ backward rate(K-2)

Question 10

Antagonists are useful to

Answer 10

block the action of hormones or neurotransmitter, identify receptors and identify enzymes etc involved in signal transduction pathways

Question 11

The antagonist Kb is ..

Answer 11

independent of the nature of the agonist

Question 12

NMDA channel can be blocked by ..

Answer 12

Mg2+ or ketamine

Question 13

Open channel block ..

Answer 13

is a form of non-competitive antagonism, the binding site for antagonist is exposed when the channel opens, has to unblock before it can close

Question 14

Hexamethonium

Answer 14

blocks sympathetic and parasympathetic ganglia. In hexamethonium man:

• Symp effects: reduced sweat and secretions, reduced vasoconstriction (vasodilation) of face, hands , lower legs and feet, impotence.
• Parasymp effects: reduced salivary secretions, loss of accomodation, slight tachycardia, impairment of gut movement

Question 15

Tubocurarine

Answer 15

is a muscle nicotinic ACh Blocker, decreases amplitude of PSP at NMJ, no AP is induced- competitive, non-depolarising neuromuscular blocker

Question 16

Suxamethonium is a depolarising, non-competitive blocker

Answer 16

It activates muscle nicotinic Rs, causes prolonged depolarisation, Na channels are inactivated; depolarising blockers are resistant to acetylcholine esterases ( but not to butyrylcholineesterase or plama esterase, therefore breakdown in 2-6 min)

Question 17

Edrophonium

Answer 17

is a short acting choline esterase inhibitor, makes a reversible ionic bond, used in the treatment of myesthenia gravis

Question 18

Dyflos, an organophosphate,

Answer 18

is an irreversible cholinesterase inhibitor, is used as inseciticide and nerve gas, reactivation with pratidoxime (transfer of phosphate )