lec 11-13. receptor theory

Question 1

occupancy

Answer 1

number of receptors occupied - related to drug concentration but NOT related to response

Question 2

radioligand binding assay

Answer 2

used to measure occupancy and deduce affinity

Question 3

scatchard plot

Answer 3

calculate affinity + number of binding sites of a receptor for a ligand

= specifically bound radioligand/concentration of nonbound ligand

Question 4

Kd

Answer 4

dissociation constant and a measure of affinity

low kd = high affinity

= -1/slope

Question 5

Bmax

Answer 5

max number of drugs which can bind specifically to a receptor if one molecule binds to each receptor

= x-intercept

Question 6

affinity

Answer 6

How tightly a drug binds to a receptor - is the same for a receptor in different tissues

it is a measure and a constant !!

Question 7

efficacy

Answer 7

capacity to produce an effect by putting the receptor in an active conformation

Question 8

EC50

Answer 8

concentration of agonist that gives 50% of the maximum response

Question 9

hill equation

Answer 9

predict response to tissue to a drug

relates drug concentration to response

slope tells number of binding sites on a receptor(???)

Question 10

full agonist vs. partial agonist

Answer 10

full have efficacy = 1
partial have efficacy <1

different efficacies produce different maximal response but they still have same EC50

Question 11

3 things that determine the effect of a drug

Answer 11

1) specificity
2) affinity
3) efficacy

Question 12

antagonist

Answer 12

inhibits the action of an agonist

Question 13

chemical antagonist

Answer 13

chemically alters agonist to prevent effect

EX. dimercaprol binding to heavy metals

Question 14

pharmacokinetic antagonist

Answer 14

lowers concentration of agonist by affect pharmacokinetic properties
EX. opiates cause constipation
EX. antibodies metabolise warfarin
EX. diuretics cause secretion

Question 15

physiological antagonist

Answer 15

cause opposing action of agonist

EX. NA increases BP, histamine lowers BP

Question 16

Non-competitive antagonist

Answer 16

blocks any process between receptor activation and response

EX. nifedipine blocks L-type Ca+ channels

Question 17

Competitive antagonist

Answer 17

competes with agonist for receptor and blocks it

this can be overridden by increasing the concentration of the agonist

Question 18

reversible competitive antagonist

Answer 18

causes a parallel shift to right and no change in maximum in a dose response curve

Question 19

dose ratio

Answer 19

quantifies parallel shifts caused by antagonists

= EC50 in presence of antagonist / EC50 in absence of antagonist

Question 20

Schild analysis

Answer 20

measure antagonist affinity

Question 21

x-intercept of schild

Answer 21

shows affinity/Kd

Question 22

pA2

Answer 22

the concentration of antagonist when double the agonist is required to have to same effect as when there is no antagonist

(logKd) x (-1)

higher pA2 = higher affinity

Question 23

constitutive receptor activity

Answer 23

a receptor which is capable of producing a biological response in the absence of a bound ligand is said to display

Question 24

inverse agonist

Answer 24

binding produces action opposite the agonist, not just prevent the action of the agonist

Question 25

desensitisation

Answer 25

rapid signal reduction in response to stimulation of cells by receptor agonists

Question 26

tolerance

Answer 26

reduction in response to a drug after repeated administration